Field Based Non-Lethal Sex Determination and Effects of Sex Ratio on Population Dynamics of Greater Amberjack, Seriola D...

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Field Based Non-Lethal Sex Determination and Effects of Sex Ratio on Population Dynamics of Greater Amberjack, Seriola Dumerili
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1 online resource (149 p.)
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english
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Smith,Geoffrey H,Jr
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University of Florida
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Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Fisheries and Aquatic Sciences, Forest Resources and Conservation
Committee Chair:
Murie, Debra J
Committee Members:
Parkyn, Daryl C
Fitzhugh, Gary

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Subjects / Keywords:
amberjack -- dumerili -- dynamics -- maturation -- nonlethal -- population -- ratio -- seriola -- sex -- sexing
Forest Resources and Conservation -- Dissertations, Academic -- UF
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Fisheries and Aquatic Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
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Abstract:
Greater amberjack, Seriola dumerili, is a pelagic reef fish that is managed in the US as two separate stocks, the South Atlantic and Gulf of Mexico stocks. The most recent stock assessment for the Gulf of Mexico stock found it to be overfished and undergoing overfishing. Sex-specific spatial distribution and exploitation may contribute to our understanding of the stock?s overexploitation because amberjack may be subject to sex-specific mortality resulting from current size regulations, sex-specific growth, and possible skewing of the sex ratio towards one sex or the other in some regions. Current assessments assume a 1:1 sex ratio for the Gulf stock. To explore the potential effect of sex ratio on the Gulf stock?s productivity, we first developed a non-lethal method of sex determination to sex greater amberjack released in an ongoing tagging study. The use of external urogenital features allowed for accurate (99.5%, n=194) sexing of greater amberjack over 500 mm FL. Urogenital catheterization provided a means of verifying sex and collecting oocyte samples from females. These samples could be used to determine the relative maturation status of females, although there could be no differentiation made between immature and mature but resting females. Analysis of sex ratios from the non-lethal sexing data and published datasets suggest that the Gulf stock likely has a male to female sex ratio in the range of 0.5:1 to 1:1 with estimates ranging from 0.4:1 to 1.1:1. To examine the influence of sex ratios on the productivity of the Gulf stock an age-, size-, and sex-structured model was used to model a number of sex ratio scenarios. In general, female-skewing, particularly in the largest size classes, lead to increased stock productivity over the assumed 1:1 sex ratio. Even moderate male-skewing could decrease productivity with some scenarios indicating a stock collapse. These results demonstrate that an incorrect assignment of a presumed sex ratio for the Gulf stock could result in it being mismanaged. It is proposed that a range of realistic sex ratio estimates for this stock should therefore be used in its assessment, rather that continuing to simply assume a sex ratio of 1:1.
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In the series University of Florida Digital Collections.
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Includes vita.
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Includes bibliographical references.
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Statement of Responsibility:
by Geoffrey H Smith.
Thesis:
Thesis (M.S.)--University of Florida, 2011.
Local:
Adviser: Murie, Debra J.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-08-31

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1 FIELD BASED NON LETHAL SEX DETERMINA TION AND EFFECTS OF SEX R ATIO ON POPULATION D YNAMICS OF GREATER AMBERJACK, SERIOLA DUMERILI B y GEOFFREY HENRY SMITH JR. A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011

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2 2011 Geoffrey Henry Smith Jr.

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3 ACKNOWLEDGMENTS I would like to thank my committee chair Dr. Debra Murie for her su pport and guidance throughout this process. I would also like to thank Dr. Daryl Parkyn and Dr. Gary Fitzhugh, who essential to the collection of greater amberjack for this research. I also thank all the members of the Murie/Parkyn lab a nd field crew for assistance with data collection. I would also like to acknowledge the School of Forest Resources and Conservation at the University of Florida for funded by Grant # NA07NMF4540076 from NOAA Fisheries Cooperative Research Program.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 3 LIST OF TABLES ................................ ................................ ................................ ........................... 6 LIST OF FIGURES ................................ ................................ ................................ ......................... 7 ABASTRACT ................................ ................................ ................................ ................................ 10 CHAPTER 1 GENERAL INTRODUCTION ................................ ................................ .............................. 12 2 NON LETHAL SEX DETERMINA TION AND SEX RATIOS OF GREATER AMBERJACK ................................ ................................ ................................ ........................ 21 Overview ................................ ................................ ................................ ................................ 21 Steroid, Hormone, and Protein Levels and Sex Chromosomes ................................ ....... 22 Palpation ................................ ................................ ................................ .......................... 23 Surgical Observation and Biopsy ................................ ................................ .................... 23 Endoscopy ................................ ................................ ................................ ....................... 24 Ultrasound ................................ ................................ ................................ ....................... 26 Urogenital Catheterization ................................ ................................ ............................... 27 External Urogenital Features ................................ ................................ ........................... 28 Method of Choice for Greater Amberjack ................................ ................................ ....... 32 Methods ................................ ................................ ................................ ................................ .. 33 Sex Differentiation of Urogenital Pores ................................ ................................ .......... 33 Field based Sex Identification using Urogenital Pores ................................ ................... 34 Accuracy of Sex Determination ................................ ................................ ...................... 34 Maturation Staging of Females using Urogenital Catheterization ................................ .. 36 Sex Ratio Determination ................................ ................................ ................................ 37 Results ................................ ................................ ................................ ................................ ..... 38 Sex Differentiation using Urogenital Pores ................................ ................................ ..... 38 Field based Sex Identification using Urogenital Pores and Accuracy of Sex Determination ................................ ................................ ................................ .............. 39 Maturation Staging of Females using Urogenital Catheterization ................................ .. 40 Sex Ratio Determination ................................ ................................ ................................ 41 Discussion ................................ ................................ ................................ ............................... 42 3 SEX RATIO EFFECTS ON POPULATI ON DYNAMICS OF GREATER AMBERJACK ................................ ................................ ................................ ........................ 69 Overview ................................ ................................ ................................ ................................ 69 Methods ................................ ................................ ................................ ................................ .. 73 Resul ts ................................ ................................ ................................ ................................ ..... 82

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5 Modeling Effects of Sex Ratios Applied at Recruitment ................................ ................ 82 Modeling Effects of Sex Ratios Resulting from Fishing ................................ ................. 85 Modeling Effects of Female ............................... 91 Sensitivity Analyses ................................ ................................ ................................ ........ 93 Discussion ................................ ................................ ................................ ............................... 94 4 CONCLUSION ................................ ................................ ................................ ..................... 133 REFERENCES ................................ ................................ ................................ ............................ 136 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ....... 148

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6 LIST OF TABLES Table page 1 1 Age and size at maturity estimates for greater amberjack from different regions of the eas tern and western Atlantic Ocean ................................ ................................ ............. 19 1 2 History of management of the Gulf of Mexico greater amberjack stock .......................... 20 2 1 Summary of non lethal sexing methods use d for a variety of fish species ........................ 50 2 2 Maturation stages of greater amberjack based on general appearance of oocytes from catheter samples ................................ ................................ ................................ ................. 55 2 3 Number of cathe terized female greater amberjack classified into each maturation stage described in Table 2 2 by month ................................ ................................ .............. 56 2 4 Number of catheterized female greater amberjack classified into each maturation st age described in Table 2 2 by 100 mm FL size class ................................ ..................... 57 2 5 Overall sex ratios, sex ratios for individuals <700 mm fork length (FL), sex ratios for ........................... 58 3 1 Input parameters for models. V alues in parentheses indicate valu es used in sensitivity analysis ................................ ................................ ................................ ........... 105 3 2 Gear selectivites for G ulf of Mexico greater amberjack ................................ .................. 106 3 3 Proportion of mature male and female Gulf of M exico greater amberjack by age ......... 106 3 4 Sensitivity analysis for Gulf of Mexico greater amberjack models with sex ratios applied at recru itment ................................ ................................ ................................ ...... 107 3 5 Sensitivity analysis for Gulf of Mexico greater amberjack models with sex ratios applied based on size. ................................ ................................ ................................ ...... 108

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7 LIST OF FIGURES Figure page 2 1 Catheter used to obtain milt and oocyte samples from greater amberjack. ....................... 59 2 2 Male urogenital region of greater amberja ck with anus, genital pore, and urinary pore denoted. The urinary pore is the most posterior structure ................................ ................. 60 2 3 Female urogenital region of greater amberjack with anus, genital pore, and urinary pore denoted. The ur inary pore is the most posterio r structure ................................ ......... 61 2 4 Urogenital region of a reproductively active female greater amberjack with the anus, genital pore, and urinary por e denot ed ................................ ................................ .............. 62 2 5 Numbers of greater amberjack non lethally sexed and numbers of greater amberj ack that had their sex verified ................................ ................................ ................................ ... 63 2 6 Nu mber of female and male greater amberjack non lethally sexed by size class with sex verified ................................ ................................ ................................ ......................... 64 2 7 Percent accuracy of non lethal sexing of greater amberjack by size class using features of t heir ur ogenital pores ................................ ................................ ...................... 65 2 8 Representative images of greater amberjack oocytes at various stages of maturity collected via uro genitalcatheterization ................................ ................................ .............. 66 2 9 Mean oocyte diamter of each oocyte type obtained from urogenital catheter samples of greater amberjack following descriptions given in Table 2 2 ................................ ....... 67 2 10 Annual ma le to female sex ratios from the Murie and Park yn (2008) dataset for 2002 2008 ................................ ................................ ................................ .......................... 68 3 1 Male spawning stock biomass (MSSB) of Gulf of Mexico greater amberjack for models with a range of sex rati os applied at recruitment over F values of 0.2 to 0.6 ..... 109 3 2 Female spawning stock biomass (FSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitm ent over F values of 0.2 to 0.6. .... 110 3 3 Total sperm production (SP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment F values of 0.2 to 0.6 ................................ ..... 111 3 4 Total egg production (EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. ........................... 112 3 5 Total fertilized egg production (FEP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment F values of 0.2 to 0.6 ............. 113

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8 3 6 Ratio of fertilized egg production to egg production (FEP/EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment ............. 114 3 7 Weighted spawn ing potential ratio (wSPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6 ..... 115 3 8 Spawning potential ratio (SPR) o f Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6 .......................... 116 3 9 Male spawning stock biomass (MSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ............... 117 3 10 Female spawning stock biomass (FSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ............... 118 3 11 Total sperm production (SP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ................................ ...... 119 3 12 Total egg production (EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F valu es of 0.2 to 0.6 ................................ ...... 120 3 13 Total fertilized egg production (FEP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ............... 121 3 14 Ratio of fertilized egg production to egg production (FEP/EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 ....................... 122 3 15 Weighted spawning potential ratio (wSPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ............... 123 3 16 Spawning pote ntial ratio (SPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6 ................................ .... 124 3 17 Male spawning stock biomass (MSSB) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ ........... 125 3 18 Female spawning stock biomass (FSSB) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ 126 3 19 Total sperm production (SP) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ ............................ 127 3 20 Total egg production (EP) for Gulf of Mexico gr eater amberjack across a range of F values ................................ ................................ ................................ ............................... 128 3 21 Total fertilized egg production (FEP) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ ............. 129

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9 3 22 Ratio of fertilized egg production to egg production for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ .............. 130 3 23 Weighted spawning potential rat io (wSPR) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ 131 3 24 Spawning potential ratio (SPR) for Gulf of Mexico greater amberjack across a range of F values ................................ ................................ ................................ ....................... 132

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10 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FIELD BASED NON LETHAL SEX DETERMINA TION AND EFFECTS OF SEX R ATIO ON POPULATION DYNAMICS OF GREATER AMBERJACK, SERIOLA DUMERILI By Geoffrey H. Smith Jr. August 2011 Chair: Debra J. Murie Major: Fisheries and Aquatic Sciences Greater amberjack, Seriola dumerili is a pelagic reef fish that is managed in the US as two separa te stocks the South Atlantic and Gulf of Mexico stocks. The most recent stock assessment for the Gulf of Mexico stock found it to be overfished and undergoing overfishing. Sex specific spatial distribution and exploitation may contribute to our understand overexploitation because a mberjack may be subject to sex specific mortality resulting from current size regulations, sex specific growth, and possible skewing of the sex ratio towards one sex or the other in some regions. Current assessm ents assume a 1:1 sex ratio for the Gulf stock. To explore the potential e ffect of sex ratio on the we first developed a non lethal method of sex determination to sex greater amberjack release d in an ongoing tagging study. The us e of external urogenital features allowed for accurate (99.5%, n=194) sexing of greater amberjack over 500 mm FL. Urogenital catheterization provided a means of verifying sex and collecting oocyte samples from females. These samples could be used to determ ine the relative maturation status of females, although there could be no differentiation made between immature and mature but resting females. Analysis of sex ratios from the non lethal sexing data and published datasets suggest that the Gulf stock likely has a male to female sex ratio in the

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11 range of 0.5:1 to 1 :1 with estimates ranging from 0.4:1 to 1.1:1. To examine the influence of sex ratios on the productivity of the Gulf stock an age size and sex structured model was used to model a number of sex ratio scenarios. In general, female skewing, particularly in the largest size classes, lead to increased stock productivity over the assumed 1:1 sex ratio. Even moderate male skewing could decrease productivity with some scenarios indicating a stock colla pse. These results demonstrate that an incorrect assignment of a presumed sex ratio for the Gulf stock could result in it being mismanaged. It is proposed that a range of realistic sex ratio estimates for this stock should therefore be used in its assessme nt, rather that continuing to simply assume a sex ratio of 1:1.

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12 CHAPTER 1 GENERAL INTRODUCTION Greater amberjack Seriola dumerili is a pelagic reef species that is found along both the eastern and western Atlantic coasts, in the Mediterranean Sea, and throughout much of the Indian and Pacific O ceans In the W estern Atlantic Ocean, greater amberjack are distributed from Nova Scotia to Brazil, including the Caribbean and Gulf of Mexico ( Smith Vaniz 1984 ) They tend to congregate around reefs, rocky outcro ppings, wrecks, and man made structures such as oil platforms ( Manooch and Potts 1997a, b; Thompson et al. 1999; Harris et al. 2007 ) which may make them susceptible to overfishing ( Beasley 1993 ) Several extensive studies on the age and growth of greater amberjack have been conducted in the Western Atlantic but relatively little research has been conducted on reproductive aspects, such as age at maturation, fecundities, and sex ratios There appear to be no external sexual characters in this species, but comparisons of ages with an adequate sample size for males and females (ages 0 8) have shown that females tend to be larger at age than males (Harris et al. 2007, Murie and Parkyn 2008) This difference in length at age was found to be significant for ages 3, 4, 7, and 9 by Harris et al. (2007) and for ages 2, 4, and 5 by Murie and Parkyn (2008) Beasley (1993) and Thompson et al. (1999) found no difference in the growth rates of males and females from Louisiana but reported that females compr ised 72% of th e fish over 1 m fork length (FL). Burch (1979) found that beginning with age 4 females were significantly longer than males in southeast Florida He also noted that the mean monthly FL for females was greater than for males and that fish greater than 120 0 mm were usually females A number of studies conducted in the Eastern Atlantic Ocean, mainly in the Mediterranean, have provided information related to various reproductive aspects, but largely focusing on captive culturing efforts (Micale et al. 1993, 1999; Marino et al. 1995a, b; Grau et al.

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13 few studies in the Western Atlantic focusing on reproduction in this species. Histological examination of gonads from gr eater amberjack in the Mediterranean has revealed that sexual differentiation is clearly evident in juveniles that are as small as 23 cm standard length (SL) [approximately 245 mm fork length (Uchiyama et al. 1984)] and 4 5 months old (Marino et al. 1995a ) It appears that amberjack in the Mediterranean may mature at much larger sizes and older ages than those in the Western Atlantic Ocean (Table 1 1). There are also discrepancies in the maturity estimates obtained for the two studies conducted in the West ern Atlantic (Table 1 1). These two studies were conducted on two stocks that are managed separately (NMFS 2006), and that are likely genetically distinct (Gold and Richardson 1998). This may be part of the reason for the disparity in the two sets of estim ates, but the differences may also be attributed to the manner in which samples were collected. Murie and Parkyn (2008) noted that Harris et al. (2007) largely targeted a known spawning aggregation with few immature fish being sampled. This would tend to disproportionately represent smaller and younger mature individuals. Murie and Parkyn (2008) also noted, however, that the majority of fish in their study were not sampled from a spawning aggregation and were immature individuals, which may have resulted i n some bias towards larger females that were not reproductively active. A range of sex ratio estimates have been calculated from different regions within the range of this species. Sex ratios (male:female) of 1:1 (Lazzari and Barbera 1989; Micale et al. 19 93), 1:2.5 (Thompson et al. 1999), and 1:1.11 (Harris et al. 2007) have been recorded from the Mediterranean, north central Gulf of Mexico, and US South Atlantic coast, respectively Burch (1979) reported a male to female sex ratio of 1:0.65 from southeast Florida with males predominating in all months except July, August, and September when females made up

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14 approximately 66% of the catch Beasley (1993) reported monthly male to female sex ratios of 1:1 to 1:2.06 from the northern Gulf of Mexico of f the coa st of Lou i siana It has been suggested that in the Gulf of Mexico greater amberjack may show some regional segregation of sexes with females being more prevalent off the coast of Louisiana and males being more prevalent off the western coast Florida, as ha s been observed for cobia Rachycentron canadum ( Thompson et al. 1999) Greater amberjack are a very fecund species with annual fecundity estimates ranging from 18 to 59 million eggs per female, with fecundity varying based on female size (Harris et al. 200 7). Greater amberjack can be classified as a multiple batch, a synchronous spawning fish due to the fact that annual fecundity is indeterminate with all stages of oocytes being present (Murua and Saborido Rey 2003; Harris et al. 2007) Spawning in greater a mberjack varies in time of year based on location and appears to coincide with a temperature increase in the spring (Jerez et al. 2006). Off the Canary Islands, greater amberjack were found to spawn between April and October (Jerez et al. 2006), in the Med iterranean spawning appears to peak between mid May and mid July (Marino et al. 1995a), and in south Florida and the Florida Keys peak spawning occurs in April and May (Harris et al. 2007). Thomspon et al. (1991) found spawning to occur in May and June off the coast of Louisiana, while Murie and Parkyn (2008) found peak spawning in the Gulf of Mexico to occur in March and April. Greater amberjack are targeted both recreationally and commercially in the W estern Atlantic Ocean In the United States, greater amberjack are managed as two separate stocks, the US South Atlantic stock and the Gulf of Mexico stock. The boundary for these stocks occurs from approximately the Dry Tortugas through the Florida Keys and to the mainland of Florida (NMFS 2006). The Gulf o f Mexico stock is managed by the Gulf of Mexico Fishery

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15 Management Council (GMFMC) Originally greater amberjack were not included in the Reef Fish Fishery Management Unit (FMU) established by the Reef Fish Fishery Management Plan (FMP) which was impleme nted in 1984 (Hood 2006). This occurred because greater amberjack were not generally targeted at this time and were considered an incidental catch, and there was also insufficient data available to estimate the maximum sustainable yield (MSY) and optimum y ield (OY) for the fishery However, increases in targeted fishing for this species and the resulting effects on the stock size have led to a number of regulatory measures, which are summarized in Table 1 2. In 1996, an assessment was conducted for the Gulf stock (McClellan and Cummings 1996), but it was deemed too imprecise to specify an acceptable biological catch or set a total allowable catch (TAC) (Hood 2006). The stock was re assessed in 2000 by Turner et al. (2000). The four most likely model runs fro m this assessment indicated that the stock was overfished. A status of overfished indicates a stock condition in which the current biomass is less than the Minimum Stock Size Threshold (MSST = (1 M )*B MSY ), where M is the natural mortality rate and B MSY is the biomass capable of producing MSY. Two of these four runs also indicated that the stock was undergoing overfishing, a condition in which the current exploitation rate ( F current ) exceeds the exploitation rate that would produce MSY ( F MSY ) (NMFS 2006). In 2001, the GMFMC was notified by the National Marine Fisheries Service that the Gulf stock was overfished. This resulted in Secretarial Amendment 2, which contained biological reference points, status determination criteria, and a 10 yr rebuilding plan (Ho od 2006) The most recent stock assessment for greater amberjack in the Gulf of Mexico (NMFS 2006) indicated that this fishery remains overfished and is undergoing overfishing This stock assessment and further ead to further regulation of the Gulf stock (Table 1 2).

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16 The 2006 stock assessment (NMFS 2006) was based on the best available data, but there was still a substantial lack of adequate information available which resulted in the use of surrogate parameter s from the US South Atlantic stock and proxies, such as weight at maturity as a proxy for fecundity Some of these data gaps, such as information on age and growth have been recently acquired (Murie and Parkyn 2008). Many aspects of reproductive biology o f greater amberjack in the Gulf of Mexico, however, are lacking, yet are critical to understanding their sustainability. Reproductive seasonality and fecundity are currently being studied (D. Murie et al., University of Florida, unpublished data), but othe r reproductive parameters, such as sex ratio, are unknown. Without information on the sex ratio for the Gulf stock of amberjack it must be assumed that it is 1:1, as was the case in the current stock assessment, although it was unknown how this would influ ence the population dynamics of greater amberjack. Regional segregation by sex, as suggested by Thompson et al. (1999), may result in regional skewing of sex ratios and hence disproportionate representation of one sex or the other in the catches from a par ticular region. There is also a potential for a disproportionate representation of females in the harvested catch due to the faster growth of females in comparison to males and the minimum size limits placed on the fisheries (i.e. sex selectivity by the fi shery) This may be particularly true in the commercial fishery where its minimum size limit of 914 mm fork length (FL) would result in a majority of very large fish being harvested, which would be mostly females. Disproportionate catches of one sex over t he other could lead to an alteration of the overall sex ratio, which may impact the population dynamics of the stock due to possible egg or sperm limitation arising from low numbers of mature individuals of a particular sex (Huntsman and Schaaf 1994; Armsw orth 2001; Alonzo and Mangel 2004, 2005; Heppell et al. 2006; Molloy et al. 2007; Alonzo et al. 2008).

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17 Obtaining data on the sex of greater amberjack landed in both commercial and recreational fisheries may be difficult and potentially biased. In the comme rcial fishery, fish are generally brought to port gutted making sexing by examination of the gonads impossible In addition, p ort sampling of the recreational fisher y sector generally only sample s a small portion of the landed catch, which may represent o nly a small fraction of the total catch due to size regulations and mandatory discarding of under sized fish. If there is sex selectivity in the landings of a fishery, sex ratios derived from fisheries data may also be biased towards the selected sex, whil e the sex ratio of the remaining, non harvested population may be different and possibly becoming skewed toward the opposite sex. The development of a non lethal sexing method for greater amberjack would allow for an alternative method of estimating sex ra tios. Such a method could be applied in the field by researchers or onboard fishery observers to determine the sex of the entire catch, including discards, rather than simply obtaining sex information by sampling a fraction of the landed catch. The overal l goal of this study was to examine the influence of sex ratios on the population dynamics of greater amberjack in the Gulf of Mexico. Specific objectives included: 1) development and validation of a non lethal method to sex fish by external examination of the urogenita l area; 2) evaluation of general maturation status of females via urogenital catheterization; 3) analysis of sex ratios based on published datasets and from field based non lethal sexing; and 4) assessment of the impact of a range of potentia l sex ratios on the productivity of Gulf of Mexico greater amberjack. A non lethal method of sexing greater amberjack was developed based on differences associated with the genital and urinary pores apparent between males and females, and validation of thi s method was obtained through the expression of milt, the collection of gonadal material (milt, oocytes, ovarian lamellae) via

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18 urogenital catheterization, and sacrificed individuals (Chapter 2). Application of this method to fish captured in an ongoing tag and release study on greater amberjack in the Gulf of Mexico allowed for an alternative means of estimating overall sex ratios, as well as sex ratios based on size. Sex ratio estimates were also obtained from published dataset (Murie and Parkyn 2008), and these two sets of sex ratio estimates, as well as previously published sex ratios from the region, were used to develop a range of potential sex ratio scenarios (Chapter 2). A size, age, and sex based population model was then used to assess the potential impacts on both male and female reproductive potential under each of these sex ratio scenarios (Chapter 3). In conclusion, Chapter 4 summarized the new information obtained during the course of this study, including the use of external urogenital features and urogenital catheterization to sex and stage female greater amberjack, the possible sex ratio trends for the Gulf stock, and the potential effects of sex ratios differing from 1:1 on the productivity of the Gulf stock.

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19 Table 1 1. Age and size at matu rity estimates for greater amberjack from different regions of the eastern and western Atlantic Ocean. First mature 50% mature Last immature Sex Age Size (mm FL) Age Size (mm FL) Age Size (mm FL) Region Reference Male 2 650 a 1150 a . Me diterranean Marino et al. 1995b 1 464 644 5 755 US South Atlantic Harris et al. 2007 Female 3 850 a 1200 a . Mediterranean Marino et al. 1995b 1 514 1.3 733 5 826 US South Atlantic Harris et al. 2007 1 501 3 4 850 900 6 Gulf of Mexico Murie and Parkyn 2008 Combined . 3 4 b Gulf of Mexico Thompson et al. 1991 a Standard length was converted to forklength (FL) using equation provided by Uhiyama et al. (1984). b All fish examined were mature by this age.

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20 Table 1 2. History of management of the Gulf of Mexico greater amberjack stock (Hood 2006; NMFS 2008, 2009 a, b, 2010 a, b). Year Amendment Regulations Justification 1990 Amendment 1 added to Reef Fish FMU ; protect stock and prevent to the Reef Fish FMP 28 in (711 mm) FL minimum size (recreational) ; 3 fish/angler bag limit (recreational) ; overfishing; landings declining since 1982; targeted more as 36 in (914 mm) FL minimum size (commercial) other target species declined in abundance 1997 Amendment 12 to the Reef Fish FMP 1 fish/angler bag limit (recreational) anecdotal information from fishermen that the average size of fish and abundance had decreased 1998 March May closure (commercial) concerns about abundance continuing to decline, reduce commerci al catch by amount similar to recreational bag limit reduction 2001 Secretarial Amendment 2 biological reference points, status determination critera, and 10 yr rebuilding plan that would limit harvest for 3 year intervals: NMFS declard the stock overfish ed in January 2001 2.9 million lbs (1.3 million kg) for 2003 2005 5.2 million lbs (2.4 million kg) for 2006 2008 7.0 million lbs (3.2 million kg) for 2009 2011 7.9 million lbs (3.6 million kg) for 2012 2008 Amendment 30A t o the Reef Fish FMP 30 in (762 mm) FL minimum size (recreational) ; zero bag limit for captains and crew of for hire vessels ; 2006 stock assessment found stock to be overfished and undergoing 0.503 million lbs (0.228 million kg) commercial quota ; overfi shing 1.368 million lbs (0.621 million kg) recreational quota 2009 temporary recreational closure (Oct 24 Dec 31) quota met or exceeded 2009 temporary commercial closure (Nov 7 Dec 31 quota met or exceeded 2010 0.373 million lbs (0.169 m illion kg) commercial quota reduction in quota for 2009 overage 2010 1.243 million lbs (0.564 million kg) recreational quota reduction in quota for 2009 overage 2010 temporary commercial closure (Oct 28 Dec 31) quota met or exceeded

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21 CHAPTER 2 NON LETHAL SEX DETERMINATION AND SEX RATIOS OF GR EATER AMBERJACK Overview An important aspect for the management of fish species and successful aquaculture programs is the ability to accurately determine the sex and maturation status of individuals. This infor mation can be used to determine parameters in the assessment of wild populations, such as sex ratios, age and size at maturation, and potential fecundity (Blythe et al. 1994; MartinRobichaud and Rommens 2001; Whiteman et al. 2005; Swenson et al. 2007). Fo r aquaculture programs to be successful the sex and maturity of individuals is needed to maintain proper sex ratios and to select fish to maintain for broodstock, as well as to aid in timing of induced spawning or stripping of eggs (Martin et al. 1983; Shi elds et al. 1993; Blythe et al. 1994; Martin Robichaud and Rommens 2001; Moghim et al. 2002; Alam and Nakamura 2008; Newman et al. 2008). However, for fish showing little (i.e. differential growth in sexes) or no sexual dimorphisms, this information is tra ditionally gained by sacrificing the fish and performing post mortem dissections for fisheries or through gonadal biopsies in aquaculture facilities (Martin Robichaud and Rommens 2001; Swenson et al. 2007). Developing a means of determining the sex and mat urity of individuals without sacrificing them is of particular interest to the management of endangered or threatened species where it is undesirable to sacrifice any individuals (Blythe et al. 1994; Moghim et al. 2002; Colombo et al. 2004; Bryan et al. 20 07), for non lethal tag and release studies (St Pierre 1992), and to aquaculture programs where this information would maximize production and profit by maintaining appropriate sex ratios without sacrificing broodstock (Martin et al. 1983; Reimers et al. 1 987; Mattson 1991; Karlsen and Holm 1994; Blythe et al. 1994; Matsubara et al. 1999; Moghim et al. 2002; Alam and Nakamura 2008). As discussed in Chapter 1, the development of a non lethal sexing technique for greater

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22 amberjack would provide an alternative means to obtain information relating to reproduction, such as calculating sex ratios, which often rely on port sampled fish that may not r epresent the entire population. Several non lethal methods have been developed to assess the sex and maturity of fish with varying degrees of success, including: 1) analyzing steroid, hormone, and protein levels; 2) determining sex chromosomes; 3) palpating the gonad; 4) surgical observation and biopsy; 5) endoscopy; 6) ultrasonography; 7) urogenial catheterization; and 8) examining external urogenital features. Steroid, Hormone, and Protein Levels and Sex Chromosomes Radioimmunoassays of several blood plasma indicators have been investigated to determine sex and maturation stage of fish. Among the blood plasma indicators used are the steroids 11 ketotestosterone, estradiol, and testosterone. In some cases these indicators can also be found in muscle fiber (Heppell and Sullivan 2000). This method has been used to determine the sex and maturation status of a number of speci es (Sangalang et al. 1978; Johnson and Casillas 1991; Heppell and Sullivan 2000; Webb et al. 2002; Evans et al. 2004; Feist et al. 2004) (Table 2 1). The detection of the female specific protein vitellogenin in the blood or skin mucus has also been used to determine the sex of some species (Le Bail and Breton 1981; Gordon et al. 1984; Takemura et al. 1996; Heppell and Sullivan 1999) (Table 2 1). Vitellogenin can be detected through the use of immunoagglutination or enzyme linked immunosorbent assay (ELISA). Methods including plasma lipophosphoprotein analysis, plasma vitellogenin concentrations, immunoagglutination, and radioimmunoassay of blood steroid and hormone levels can be successful in identifying the sex of individuals, but they have several draw ba cks. The collection of blood and/or oocytes involved with several of these methods may cause

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23 excessive stress, introduce pathogens, and delay or prevent ovulation (Blythe et al. 1994; Moghim et al. 2002). These methods may be costly, do not provide immedia te results, and may only be accurate if fish are mature or only during certain periods during the reproductive cycle (Martin et al. 1983; Blythe et al. 1994; Martin Robichaud and Rommens 2001; Moghim et al. 2002; Colombo et al. 2004), and in the case of bl ood plasma indicators, the technique is species specific with a baseline needed for each species examined (Colombo et al. 2004). Analysis of genetic samples for sex chromosomes can also be used to sex some fish species. However, a number of species, inclu ding greater amberjack, lack sex chromosomes (Sola et al. 1997). Palpation Palpation of the gonad by insertion of the finger through the mouth and into the stomach has allowed for accurate sexing of several small salmonid species (Kano 2005) (Table 2 1). T his method is relatively noninvasive but is limited by the size and species of fish that can be examined. In small fish a finger may be too large to insert into the mouth, while in large fish a finger may not be long enough to reach the stomach and theref ore cannot be used to feel the gonads through the wall of the stomach. Also, species with pharyngeal teeth, such as carp Cyprinus carpio or species with other types of teeth that could potentially injure the investigator, cannot be sexed with this method (Kano 2005). Surgical Observation and Biopsy Performing surgeries on live fish to directly examine the gonads and to remove a gonadal sample for biopsy has been used to determine the sex and maturation status of several species (Ritchie 1965, Alam and Nak amura 2008) (Table 2 1). In some cases this method has become a standard practice for determining the sex and maturity of fish, most notably in sturgeon (Johnson and Casillas 1991; Kynard and Kieffer 2002; Webb et al. 2002; Colombo et al. 2004; Feist et al

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24 2004) Alam and Nakamura (2008) performed surgery on honeycomb grouper Epinephelus merra in a lab setting to extract gonadal tissue for biopsy This method resulted in 100% correct identification of sex and maturity with no serious infections or deaths r esulting, and apparently no lasting damage to the gonads (Table 2 1). In some species, gonadal samples for biopsy may be obtained by insertion of forceps into the urogenital pore. This method has been used on striped bass Morone saxatilis with an accuracy of 95%, but some fish had gonadal wounds that had not healed at autopsy (Ritchie 1965) (Table 2 1). Gonadal biopsies performed on live fish can result in very accurate identification of sex in many cases, but it may prove less accurate for some species an d for immature individuals where collection of gonadal tissue is difficult (Johnson and Casillas 1991; Webb et al. 2002). Accuracies of gonadal biopsies may also be reduced when adipose tissue or tissue from other organs is mistakenly collected instead of gonadal tissue (Webb et al. 2002). Biopsies on live fish are also invasive and have the potential to cause trauma to the gonad (Moccia et al 1984; Mattson 1991; Johnson and Casillas 1991; Kynard and Kieffer 2002; Webb et al. 2002; Colombo et al. 2002). Thi s technique may be difficult, if not impossible, to perform on a moving boat in the field without causing injury to the fish. Also, an anesthetic that is approved for immediate release of fish must be used for studies done in the field, especially in fish that may be consumed, and fish must be fully revived before they are released to reduce post release predation (Columbia Basin Fish and Wildlife Authority 1999; Coyle et al. 2004; Kahn and Mohead 2010). Endoscopy Endoscopy involves the insertion of an endo scope either through the urogenital pore or a small incision in the abdomen, where the gonads are viewed either through the urogenital duct or directly. An otoscope, a device normally used for examining the interior of the human ear, was

PAGE 25

25 one of the first d evices to be used as an endoscope for determining sex in fish. It allowed largemouth bass Micropterus salmoides to be sexed with high accuracy (Driscoll 1969) (Table 2 1). Typical devices used for endoscopy of fish are borescopes, rigid or flexible devices with an eyepiece on one end and an objective lens on the other linked by a relay optical system surrounded by optical fibers, or endoscopes, which have the same components as a borescope but also contain a channel for the insertion of instruments or manip ulators Both devices can be used with a video imaging system Endoscopy has been used to successfully determine the sex and maturational status of a number of species (Moccia et al. 1984; Ortenburger et al. 1996; Kynard and Kieffer 2002; Wildhaber et al. 2005; Bryan et al. 2007; Swenson et al. 2007) (Table 2 1). Examination of gonads by endoscopy provides immediate results and in at least some cases can predict sex accurately throughout the reproductive cycle. However, this technique requires some experti se and a detailed knowledge of the internal anatomy of the body cavity of the fish species being examined. In addition, this is still an invasive method, particularly when an incision needs to be made. The stress involved, along with the loss of epidermal mucus, drying of skin, and damage to internal organs could potentially lead to mortality (Swenson et al. 2007). There is also the potential for later complications, such as an incision reopening or infection (Swenson et al. 2007). Endoscopy can also be a r elatively lengthy process, from the time a fish is anesthetized until the time it is revived can range from 2 to 10 minutes on average (Moccia et al. 1984; Ortenburger et al. 1996; Swenson et al. 2007). Video endoscopy has been successfully used in the fie ld, but it has only been performed from a shore base. As with gonadal biopsies, this technique may be difficult, if not impossible, to perform on a moving boat without causing injury to the fish. In addition, an anesthetic is often needed and would have si milar limitations as with surgical biopsies

PAGE 26

26 Ultrasound Ultrasound imaging has been used to accurately determine the sex of a number of fish species throughout much of their various reproductive cycles (Martin et al. 1983; Reimers et al. 1987; Mattson 199 1; Bonar et al. 1989; Blythe et al. 1994; Karlsen and Holm 1994; Matsubara et al. 1999; Martin Robichaud and Rommens 2001; Moghim et al. 2002; Burtle et al. 2003; Colombo et al. 2004; Wildhaber et al. 2005; Whiteman et al. 2005; Newman et al. 2008) (Table 2 1) It has also been used to determine the maturational status of a number of species (Reimers et al. 1987; Shields et al. 1993; Blythe et al. 1994; Martin Robichaud and Rommens 2001; Moghim et al. 2002; Burtle et al. 2003; Evans et al. 2004; Bryan et a l. 2005, 2007; Newman et al. 2008) (Table 2 1). Gonad diameter can be estimated in some cases, which could allow for the estimation of a gonadosomatic index (size of gonads relative to the fish size) or the development of a similar reproductive index (Matt son 1991; Newman et al. 2008). Pulse echo acoustic microscopy, which is essentially an adaptation of ultrasound imaging using a focusing lens to concentrate the high frequency ultrasound to produce high resolution images, has been shown to be an effective means of sexing larval sea lampreys Petromyzon marinus (Maeva et al. 2004). This technology would likely produce similar results in larval or small juvenile fish of other species and has the potential to be adapted to field use. Ultrasound technology has also been used in several cases to determine batch fecundity estimates. Fecundity estimates for striped bass, which were comparable to fecundity estimates obtained via traditional methods in previous studies, have been determined by estimating ovary volume from ultrasound images and collecting oocyte samples via a catheter (Will et al. 2002; Jennings et al. 2005). Fecundity estimates for red hind Epinephalus guttatus have also been made using this method (Whiteman et al. 2005), which fell within the ranges of other published estimates for this species. Fecundity estimates for Neosho madtoms Noturus placidus based on

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27 oocyte and ovary volumes calculated from ultrasound images were found to be similar to those of other madtom species (Bryan et al. 2005). The fe cundity of shovelnose sturgeon Scaphirhynchus platorynchus was determined using ovary volumes calculated from ultrasound images in combination with oocyte volumes calculated from ultrasound images and oocyte samples (Bryan et al. 2007). Ultrasound images c an provide rapid and immediate results, and the method is noninvasive. However, as with endoscopy, considerable expertise in the use of the equipment and a detailed knowledge of the internal anatomy of the body cavity of the species being examined is requ ired. In some cases sex can only be determined by the presence or absence of ovar ies as the testes can be difficult to discern The accuracy of ultrasound tends to be lessened in immature and post spawn ed individuals The size, shape, and composition of sc ales and the thickness of the abdominal wall may also influence the accuracy of this method. Anesthesia is not necessary, but may be desirable for producing better image quality. Ultrasound can also be particularly cost prohibitive in obtaining a unit with the proper resolution needed for accurate determination of sex and maturation status. Urogenital Catheterization Urogenital catheterization involves the insertion of a small diameter glass or plastic catheter into the urogenital or genital pore to collec t a gonadal sample. The sample is either collected by mouth suction or suction via syringe as the catheter is slowly pulled back out of the gonad. The diameter of the catheter used generally depends on the size of the fish, urogenital pore, and eggs to be sampled. The relatively small diameter of the vas deferens can prevent catheterization in males of some species (Ross 1984; Benz and Jacobs 1986). Determination of sex and maturational status has been obtained with the use of urogenital catheters on a numb er of species (Shehadeh et al. 1972; McEvoy 1983; Ross 1984; Garcia 1989; Bailey and Cole 1999;

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28 Mackie 2000, 2003; Alvarez Lajonchre et al. 2001; Coward and Bromage 2001; 2001 ; Asturiano et al. 2003; Marino et al 2003; Mylonas et al. 2003, 2 004; Ferraz et al. 2004) (Table 2 1). Sexing data may not always be reliable as it is often difficult to extract oocyte samples via catheterization from immature and non reproductive females (Mackie 2000, 2003). Several studies have shown that oocyte sampl es obtained via catheterization are not significantly different from samples taken directly from ovaries of the same fish post mortem, and these samples are representative of the whole ovary in species showing synchrony in ovarian development (Shehadeh et al. 1972; Garcia 1989; Alvarez Lajonchre et al. 2001; Coward and Bromage 2001; Ferraz et al. 2004). Urogenital catheterization may provide information on sex and maturity; however, in immature and non reproductive fish, as well as males in some species, it may be difficult to obtain samples. This is a relatively rapid and inexpensive sampling technique that requires little training. It can also be easily used in the field. Few deleterious effects of catheterization have been reported in studies using this method. However, it is invasive and is thought to cause stress, harm, and even direct mortality (Blythe et al. 1994; Martin Robichaud and Rommens 2001; Kynard and Kieffer 2002; Moghim et al. 2002; Newman et al. 2008). External Urogenital Features Severa l methods of evaluating the sex of fish externally have been developed involv ing direct examination of the urogenital area. These methods have been applied to a variety of fish species with varying degrees of success. Some of these methods are relatively i naccurate, while others have consistently shown accuracies comparable to the methods discussed above (Table 2 1). One of the simplest and most obvious ways to sex fish externally is through the expression of milt or eggs by pressure applied to the abdomen. This method is restricted to the time immediately surrounding spawning (Parker 1971; Casselman 1974) and generally has to be

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29 combined with some other external method, such as the presence of a swollen vent, to provide high accuracies ( Snow 1963 ; Benz and Jacobs 1986). In some species this method may not be reliable because dense abdominal musculature may prevent the expression of milt and eggs (Mylonas et al. 2004). Other external methods of sexing fish rely on finding some morphological difference in the urogenital area of the fish. In some of these methods, sexing is based on morphological features in the area surrounding the urogenital pore(s). The sex of largemouth bass can be determined by the shape of the scaleless area surrounding the urogenital ope nings (Parker 1971). In males this area is nearly circular in shape, while in females it is elliptical or pear shaped. This method did not appear to be influenced by size but may have limitations associated with size and condition of the fish (i.e. distend ed abdomen due to food and/or roe or concave abdomen due to emaciation) (Parker 1971; Manns and Whiteside 1979). The presence of a swollen reddish genital papilla in female largemouth bass can also be used to sex largemouth bass, but this method is only se asonally accurate (Benz and Jacobs 1986). In adult rock bass Ambloplites rupestris the shape and color of the urogenital papillae, the shape of the scaleless area surrounding the urogenital and anal pores, and the distance between the urogenital and anal o penings can be used as an indication of sex (Noltie 1985) In males the urogenital papilla is pointed and black at the tip, the scaleless area is circular, and the relative distance between the urogenital and anal pores is smaller than in females In fema les the urogenital papilla is blunt, swollen, and red at the tip and the scaleless area is oval in shape Some of the characters associated with this method are related to spawning, and thus accuracy may be reduced when these characters are not fully deve loped. The appearance of the urogenital area of northern pike Esox lucius has been used to sex males and females with a high degree of accuracy regardless of

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30 maturity or season (Casselman 1974). In females, the area between the anus and urogenital pore con tains many longitudinal folds, while males have only up to three slight grooves in this area. The area is often raised above the surrounding tissue in females, especially near spawning, while in males it is almost always level with the surrounding tissue. Several methods use the shape and/or number of urogenital pore(s) to determine sex. Mature bluegill Lepomis macrochirus were sexed with 100% accuracy based on the shape of the urogenital pore and the appearance of the surrounding tissue (McComish 1968). I n females, the urogenital pore resembles a doughnut like ring surrounded by pink, fleshy tissue. The male urogenital pore never has a ring like appearance, and instead it is small and funnel shaped, and is surrounded by little, or no, pink fleshy tissue. T his method appeared to only be dependent on the maturity of the fish and was not influenced by season. The depth and angle of penetration of a probe into the urogenital pore of largemouth bass can yield high sexing accuracies (Benz and Jacobs 1986). In mal es the penetration of a probe is shallow and perpendicular to the ventral surface of the fish, while in females the probe penetration is deeper and oblique to the ventral surface of the fish. Sigler (1948) found that white bass Morone chrysops could be sex ed externally based upon the number of urogenital pores. In males there was a single urogenital pore, while in females there were separate genital and urinary pores. A small pit just posterior to the urogenital pore in males could be mistaken as a urinary pore, but the use of a blunt probe eliminated this potential source of error. In boccacio Sebastes paucispinis the opening for the genital and urinary duct occur on a common urinary papilla in males, while in females the genital opening is present between the anus and the urinary papilla (Moser 1967). This anatomical trait was successfully used to sex both quillback rockfish S. maliger and copper rockfish S. caurinus in the field, underwater at 25 m depth (Murie 1991). Channel catfish Ictalurus punctatus ca n be

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31 sexed with an accuracy of 99%, regardless of body size and maturity, based on the number of urogenital pores (Norton et al. 1976). In males there is a single urogenital pore, while females have a genital pore and a urinary pore separated externally by a septum. In Pacific halibut Hippogl o ssus stenolepis the shape of the cloaca could be used to accurately sex individuals 52 cm or larger with an accuracy of 98% (St Pierre 1992) In females the cloaca is a small cone shaped projection with the terminal e nd angled towards the anal fin Males have a cloaca that is also cone shaped, but it is truncated and oriented nearly perpendicular to the body In halibut, t he genital vent of males is much larger than that of females The inability to sex smaller individ uals is partially attributed to the smaller size of the cloaca in these individuals making it difficult or impossible to view with the naked eye The sex of several North American sturgeon species has been determined in live individuals based on the shape of the urogenital opening (Vecsei et al. 2003). In males, the urogenital opening is in the shape of the letter Y, while in females it is in the shape of the letter O. This method was unreliable in dead specimens as the rectum is generally prolapsed causing the urogenital opening to protrude. In the aquaculture of various tilapia species the sexes are separated based on the number of urogenital pores (Rakocy and McGinty 1989; Popma and Masser 1999). In males there is only one urogenital pore, while in female s there are separate genital and urinary pores. Applying dye to the urogenital region can increase the accuracy of sexing and may allow for the sexing of smaller individuals (Rakocy and McGinty 1989; Popma and Masser 1999). External sexing methods based on morphological differences of the urogenital region generally result in high accuracies, and in many cases may not be restricted by size, maturity, or season. Several of these methods are completely non invasive, while others are only minimally invasive re quiring a probe to be inserted into the urogenital pore(s). These procedures are quick,

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32 do not require anesthesia, and require little training, which are all desirable for application in the field. However, maturation status cannot be obtained through exte rnal sexing methods other than through stripping milt and eggs by applying pressure to the abdomen. Method of Choice for Greater Amberjack Using previous studies of other species as a guide, a non lethal sexing methodology for field based sexing of greater amberjack needed to meet several criteria, including being minimally invasive and having a high accuracy at various sizes/ages and stages of maturity. Methods requiring minimal training, having low cost, and providing immediate results were also desirable Based on these criteria, ultrasonography, external examination of the urogenital pores, and urogenital catheritization appeared to be appropriate as methods to investigate in greater amberjack. Preliminary attempts were made to sex greater amberjack wit h ultrasonography using a portable ultrasound unit ( Carewell CUS 3000 with a LU2 2/7.5MHz linear array probe) loaned by C. Koenig (Florida State University). However, images of the organs in the body cavity were not clear enough to discern the gonads. This lack of clarity applied to amberjack specifically since comparable ultrasound of a striped bass produced images that were clearer, although still not conclusive. This particular ultrasound unit may not have had a high enough resolution for sexing of amber with higher resolution are available, but were cost prohibitive. In addition, the high content of guanine crystals in the thick epidermal tissue, peritoneum, and gas bladder of a mberjack may also have affected the quality of the image (D. Parkyn, University of Florida, personal communication ). The use of ultrasonography was therefore not considered a viable option for sexing greater amberjack.

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33 The use of urogenital catheterization was also appealing due to its minimal cost, minimal invasiveness, lack of anesthesia, and lack of extensive training. However, it may be largely limited by size and maturity of the fish being examined. Using external urogenital features for non lethal sex ing also has a number of desirable characteristics including: minimal invasiveness, minimal training, relatively rapid to perform, provides immediate results, and not being cost prohibitive. The major potential drawbacks to this method are the potential fo r size or maturation limitations and the lack of information on maturational status. However, a number of species sexed via this method have shown minimal size and/or maturation limitations, and combining this method with urogenital catheterization could p rovide some information on maturation status. In addition, the use of urogenital catheterization has been successfully used on mature greater amberjack ( ). The overall goal was to develop a non lethal method of sexing greater amberjack in the field, with specific objectives: 1) to determine the accuracy of using external urogenital features to sex greater amberjack; 2 ) to examine the utility of using urogenital catheterization as a method of determining the gonadal maturation of female greater amberjack; and 3) to directly apply non lethal sexing of field sampled greater amberjack as an alternative method of determinin g sex ratios compared to estimates obtained from data collected in previous studies using lethal methods. Method s Sex D ifferentiation of U rogenital P ores Initially, 8 (6 males and 2 females) greater amberjack were collected as part of an ongoing tagging st udy (D. Murie and D. Parkyn, University of Florida, unpublished data) in November 2008 to January 2009, and were sacrificed to examine their urogenital regions for the presence of morphological differences in the urogenital pores and surrounding tissues. A dditional

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34 observations were made on 3 individuals (1 male and 2 females) that were sexed in the field and sacrificed for validation in March 2009. A blunt probe was used to locate the anus and urogential pore(s), and differences in the spacing, location, a nd general appearance of the urogenital pore(s) and surrounding tissues was noted. Field based S ex I dentification using U rogenital P ores To apply the external sexing of amberjack to field samples, and determine the accuracy of the method, amberjack were se xed in the field during tagging trips in March 2009, April 2009, May 2009, November 2009, March 2010, April 2010, and June 2010. Fish were caught with hook and line and bandit fishing gear off the coast of Little Torch Key, Madiera Beach, Suwannee, and Apa lachicola, FL, and Grande Isle, LA. Fish were measured for fork length (FL, nearest mm), tagged below the anterior portion of the second dorsal fin with a dart tag, and 2 to 3 fin rays between rays 3 and 6 of the left pectoral fin were removed for ageing a nd genetic analysis as part of the tagging study. Fish were then sexed by examining external features of their urogenital region. To do this, a blunt probe was used to find both the genital and urinary pore and then the fish was scored as a male or female based on the location of each pore in relation to the other, and the appearance of the pores and surrounding tissue, using the sexing differentiation criteria. Accuracy of S ex De termination Validation of the field based sex identification was obtained thr ough urogenital catheterization, the expression of milt on insertion of a blunt probe into the genital pore or through abdominal pressure, and sacrificed individuals. Fish that were captured with oocytes extruded out the genital pore or that were freely fl owing milt were not used to determine accuracy of the external sexing method.

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35 Sexing and catheterization of fish was performed while they were placed on their side on a measuring board. During the initial use of this method in the field on live fish, it wa s discovered that when locating and examining the genital pore with a blunt probe, mature male fish would often express milt if the probe was inserted a few mm into the genital pore. After finding this, a blunt probe was inserted into the genital pore of a ll fish large enough to do so in an attempt to express milt as a means of sex verification. Urogenital catheterization was attempted on all females that appeared to be reproductively active, as well as randomly on both males (that did not express milt) an d females of various sizes. The catheter used consisted of a 3 ml Luer Lok tip disposable syringe and plastic microbore tubing with the following specifications: inner diameter of 0.76 mm, outer diameter of 2.23 mm, wall thickness of 0.76 mm, and length of ~20 cm (Figure 2 1). The tubing was thread style to 500 series barb adaptor (part # FTLL004 1) from Value Plastics, Inc. The catheter was gently inserted into the genital pore as far as possible, and then was slowly removed while applying suction with the syringe. The distance the tubing could be inserted depended on the size and reproductive status of the fish. In general, in smaller fish (<800 mm FL) the tubing was inserted approximately 4 8 cm, while in larger fish the tubing could be inserted farther (8 12 cm or more in some cases). In females that were reproductively active the catheter was inserted the same distance based on size described above, but because of the enlarged size of the ovarie s it could be inserted to a greater distance to obtain a larger oocyte sample if desired. Milt samples were also obtained via catheterization for several males that did not express milt following the same procedure outlined above. All samples obtained from the catheter were placed in 20 ml scintillation vials containing

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36 5 ml of 10% phosphate buffered formalin (PBF). The catheter was rinsed with deionized water between each use. A subsample of fish that did not express milt and that yielded no sample from c atheterization were sacrificed for validation of the sex determination. These sacrificed fish were initially sexed in the field based on the appearance of the urogenital area. In the lab, these same fish had their urogenital area wiped clean to remove any expelled reproductive material and waste by a colleague not involved with the sex determination project. Each fish was then re sexed without a priori knowledge x was then determined by direct visual inspection of the gonads. Maturation S taging of F emales using U rogenital C atheterization To investigate the maturation status of female fish that were catheterized, the oocyte samples were viewed under a dissection microscope at 10 50X depending on the size of the oocytes. A Motic Imaging System was used to measure the diameter of 50 oocytes or as many as possible when there were less than 50 measurable oocytes extracted via catheterization. All hydrated oocytes wer e measured. The measured oocytes were classified as primary growth oocytes (up to late perinucleolus stage), early development oocytes (stages between late perinucleolus stage and up to cortical alveolus stage), late development oocytes (lipid granule stag es), and hydrated oocytes (fully hydrated oocytes) based on their size and general appearance (Grau et al. 1996; Micale et al. 1999; Poortenaar et al. 2001; and Harris et al. 2004, 2007). Degraded oocytes were not measured, but their presence was noted. Ba sed on the most advanced type of oocytes present in the catheter samples, an individual female was classified as immature/resting (primary growth oocytes), early developing (early developing oocytes), late developing (late developing oocytes), ripe (hydrat ed oocytes or late developing and degraded

PAGE 37

37 oocytes), or spent (early developing and degraded ooctytes, but no late developing oocytes) (Grau et al. 1996; Micale et al. 1999; Poortenaar et al. 2001; and Harris et al. 2004, 2007) (Table 2 2). The size freque ncies of oocytes in these stages were plotted and compared to ranges given in Grau et al. 1996, Micale et al. 1999, and Harris et al. 2007. No differentiation could be made between immature and resting fish, as this differentiation is based mainly on small er oocyte stages that are not easily extracted with catheters and on differences in the thickness of the ovarian wall and the presence of muscles bundles in the oviarian lamellae (Grau et al. 1996; Mackie 2000; Harris et al. 2004, 2007). Numbers of fish cl assified in each maturation stage for each 100 mm FL size class were calculated on a monthly basis, which was used to determine the size of fish and time of year that catheterization provided the most detailed information regarding reproductive stage. Sex Ratio Determination Sex ratios of greater amberjack in the Gulf of Mexico were determined using published literature or data sources, as well as applying non lethal sexing of fish collected in field based sampling as an alternative method. Overall sex rati o estimates have been given in several prior studies focusing on age, growth, and reproduction of greater amberjack in the Gulf of Mexico and the US South Atlantic. The dataset used in an age, growth, and reproduction study of Gulf of Mexico amberjack by M urie and Parkyn (2008), which contained sex information on over 1600 individuals, was analyzed for estimates of overall sex ratio, as well as sex ratios based on several size classes. Sex ratios of fish < 700 mm fork length (FL) were analyzed to estimate t he sex ratios of fish below the recreational size limit. The current (2011) recreational size limit is 762 mm FL, however, from 1990 2008 the recreational size limit was 711 mm FL (28 in), and 700 mm FL therefore represents the nearest 100 mm FL size class to this size regulation. Sex ratios

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38 mm FL were analyzed as i t has been noted in a number of previous studies that greater amberjack over a meter in length are predominantly females (Beasley 1993; Thompson et al. 1999; Harris et al. 2007). Annual sex ratio estimates from the Murie and Parkyn (2008) dataset were rest ricted to 2002 2008, as yearly sample sizes prior to 2002 were low (<50 sexed fish per year). These annual sex ratios were calculated to give an estimate of the range of the overall observed sex ratios, in addition to an overall sex ratio for all years com bined. As an alternative method of calculating sex ratios, data from greater amberjack that were non lethally sexed in conjunction with an ongoing tag and release study in the Gulf of Mexico and off the Florida Keys (D. Murie and D. Parkyn, University of F lorida, unpublished data) were analyzed. Sex ratios were calculated in the same manner as for the Murie and Parkyn (2008) dataset for consistency, and separate estimates were derived for fish sampled in the Gulf of Mexico and from US South Atlantic water s off the Florida Keys. Results Sex Differentiation using Urogenital Pores Urogenital pores of both male and female greater amberjack were surrounded by white, papilla like folds of tissue (Figures 2 2 and 2 3). In addition, both males and females were found to have separate urinary and genital pores. However, the positions of these pores in relation to one another were different. In males, the genital pore lies along the midline with the urinary pore located directly posterior to it. The two pores are separa ted from one another by a thin (generally 1 mm), flesh colored septum (Figure 2 2). The septum dividing the two pores extended over the urinary pore and on insertion of a probe into the urinary pore it generally covers the genital pore and vice versa, mak ing it difficult to observe both pores at one time. In females, both the genital and urinary pores were observed to either both lie along the midline or to have one pore lie along

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39 the midline and one pore to be positioned slightly off center. The two pores were separated by a greater distance than in males, and in most cases the tissue between the pores was at least partially white in color. In some cases the white, papilla like folds of tissue that surround the urogenital pores extended between the two por es in females (Figure 2 3). The greater separation of the pores in females allowed for easier viewing of both pores simultaneously, even upon insertion of a probe, compared to males. Observation of live mature females in spawning condition revealed that th eir genital pore was much larger than that of males and was often crescent shaped (Figure 2 4). Field based S ex I dentification using U rogenital P ores and Accuracy of Sex Determination A total of 379 greater amberjack were sexed in the field via characters associated with the urogenital pores (204 males and 175 females). Of these, verification of sex was obtained for 194 individuals (95 males and 99 females). Verification was obtained mainly via expression of milt for males and via catheterization for femal es (Figure s 2 5 and 2 6). Males <800 mm FL had their sex verified primarily by catheterization (Figure 2 6). Only 4 individuals (2% of the verifications) had their sex veri fied through dissection (Figure 2 5). In total, 193 fish were sexed correctly yieldi ng an overall accuracy of 99.5%. All males ( n = 95) were sexed correctly in the field, and females ( n = 99) were sexed correctly 99.0% of the time in the field (Figure 2 7). The one individual that was incorrectly sexed in the field was a female that was s acrificed, and she was correctly sexed in the lab using characters associated with the urogenital pores prior to direct observation of her gonads via dissection. Both male and female greater amberjack of all sizes were accurately sexed, except for the one female that was 636 mm FL (Figure 2 7).

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40 Maturation S taging of F emales using U rogenital C atheterization All stages of maturation were observed in females catheterized over a sampling time frame of March to November, including females with oocytes classif ied as immature or resting (Figure 2 8A), in stages of early development (Figure 2 8B), in late stages of development or ripe and spawning (Figure 2 8C), and spent (Figure 2 8D). Of the 97 catheter samples of oocytes obtained, 92 could be staged (Table 2 3 ) according to the criteria outlined in Table 2 2. Females catheterized ranged in size from 534 mm FL to 1412 mm FL (Table 2 4) and maturity stages of early development and late development could be differentiated in females as small as 800 mm FL (Table 2 4). In addition, a number females >800 mm FL collected during the peak of the spawning season (March May) could be identified as actively spawning (ripe) based on the presence of hydrated oocytes or the co occurrence of lipid granule stage oocytes and degr aded oocytes from a prior spawning event (Tables 2 3 and 2 4). The mean diameter of measured oocytes showed distinct separation in the sizes of each category of oocyte used to determine maturation status of catheterized females (Figure 2 9). This size sepa ration in oocyte categories indicated accurate classification in determining the maturation status of females. Catheter samples from five fish did not contain visible oocytes when examined at magnifications up to 50x. However, the tissue obtained from the se five fish did not resemble milt in color or texture, but did resemble tissue surrounding oocytes from other samples both in color and texture. Also, at higher magnification (up to 100x), some structures that loosely resembled oocytes were visible. These samples were all relatively small and likely came from immature or resting females.

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41 Sex Ratio Determination Overall sex ratio estimates for greater amberjack in the Gulf of Mexico indicated that it was near 1:1 (non lethal sexing) or had a moderate femal e skew (Murie and Parkyn 2008 dataset) (Table 2 5). Yearly sex ratio estimates from 2002 2008 from the Murie and Parkyn (2008) dataset had a mean value of 0.55:1 (m:f) but showed variation in the degree of female skewing for the various years (Figure 2 10) Beasley (1993) and Thompson et al. (1999, which skewed sex ratio for greater amberjack off Louisiana, with fish >1000 mm FL showing a marked female skewed sex ratio (Table 2 5). An overall male to female sex ratio of 1.07:1 was obtained for fish from the Florida Keys (US South Atlantic) via non lethal sexing (Table 2 5). Previous sex ratio estimates for greater amberjack from the US South Atlantic stock indicated a near 1:1 or mo derately male skewed (1.5:1) sex ratio (Burch 1979, Harris et al. 2008) (Table 2 5). Mexico were relatively similar to their corresponding overall sex ratios (Table 2 5) However, sex ratios based on the dataset of Murie and Parkyn (2008) indicated a female skewed sex ratio for all sizes of fish. Sex ratio estimates for fish >1 m FL were female skewed in both the non lethal sexing of fish in the Gulf of Mexico and the Flo rida Keys, as well as in the dataset of Murie and Parkyn (2008) for the Gulf of Mexico (Table 2 5). Previous sex ratios estimated for fish > 1 m FL have also shown female skewing (Beasley 1993; Thompson et al. 1999; Harris et al. 2007). Overall, the averag e sex ratio for fish > 1 m FL in the Gulf of Mexico was 0.43 0.02 ( SE).

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42 Discussion The use of urogenital pore characteristics to non lethally sex greater amberjack in the field yielded accuracies greater than or comparable to (99 and 100% for females a nd males, respectively) a number of previous studies using similar methods on a variety of species summarized in Table 2 1. The accuracies obtained in this study were also comparable to or greater than the accuracies obtained in studies using a number of o ther possible non lethal sexing techniques on different species, including steroid, hormone, and protein levels, surgical biopsy, endoscopy, and ultrasound imaging (Table 2 1). The method of sex determination used for greater amberjack in this study was ad apted from these existing methods used on other species and it is likely that the general approach could therefore be applied to other species found to be sexually dimorphic with respect to their urogenital pores. For example, this method could easily be a dapted to other Seriola species, both those found in the Gulf and elsewhere in the world. One relatively large female almaco jack S. rivoliana that was retained during sampling for this study had the same urogenital features exhibited by greater amberjack. The single, small female that was incorrectly sexed in the field was sampled during one of the first applications of the urogenital pore method on live individuals, and she was later successfully identified in the lab as a female prior to dissection. Othe r than this one female, the method of sexing greater amberjack using urogenital characteristics was accurate regardless of sex or size of fish. Perhaps the greatest limitation of applying the method was that fish <500 mm FL had such small urogenital pores that no attempt was made to sex them. Although it was not observed in this study, small urogenital pores may also contribute to incorrectly sexing fish between 500 and 700 mm FL, particularly during the initial training and application of this method. The most common mistake would likely be to misidentify immature females in this size

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43 seen in larger females or mature females within this size range. It may be possibl e to improve this method for smaller fish by using a magnifying glass, but it may also be the case that the differences observed for larger fish may not have fully developed in smaller individuals. The use of dyes applied to the urogenital area has been us ed to improve the sexing of some species where male have a common urogenital opening, but for these species the difference is in the number of pores in each sex and not the position of the pores relative to one another (Rakocy and McGinty 1989; Popma and M asser 1999). The general maturation stage of female greater amberjack was easily obtained by examining oocyte samples extracted using urogenital catheterization. This was not an unexpected outcome, as urogenital catheterization has been used in monitoring egg maturation of this species in prior studies on captive spawning ( ). The upper end of the size frequencies of the oocytes measured in this study tended to be slightly larger than those given in Grau et al. 1996, Mi cale et al. 1999, and Harris et al. 2007, which may have resulted from regional differences in egg diamteters or from differences in preparation of the samples. Oocyte diameters in this study were obtained from whole preserved oocytes, while those from the previous studies were obtained from histological sections that may have resulted in some shrinkage. Other than this small discrepancy the egg diameters from this study corresponded well with previous studies. This, along with the distinct separation in t he mean diameters of each oocyte type, indicated that the classification of an individual to a particular maturation stage based on the types of oocytes present based on their general appearance was accurate. Although maturation staging was possible for sp awning females, it was not possible to distinguish between immature versus mature but resting females because this distinction is generally reliant on the appearance of tissues other than oocytes, such as the tunic and muscle

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44 bundles, which are not possibl e to observe using a catheter alone. However, the use of urogenital catheterization could be used to identify potential spawning aggregations of greater amberjack based on the presence of females with oocyte samples that would be classified as hydrated, in dicating that that individual was ripe. It also cannot be ruled out that some fish that were assigned a particular maturation stage did not contain more advanced oocytes that were not collected via the catheter, as catheter samples from live fish were not compared to biopsy samples from the gonads of the same individual post mortem. However, previous studies with different species have shown that catheter samples generally agree with gonad biopsies from the same individuals (Shehadeh et al. 1972; Garcia 198 9; Alvarez Lajonchre et al. 2001; Ferraz et al. 2004). The maturation status of males through obtaining catheter samples was not investigated as it would generally be assumed that if a male were producing milt that it was mature. However, some prior studi es have looked at the number or percentage of motile spermatozoa, and the duration of spermatozoa motility, from samples collected via catheterization of captive male greater amberjack prior to induced spawning during their aquaculture ( et a l. 2001; Mylonas et al. 2004). Non lethal sexing of greater amberjack, as well as other fishes, can have a variety of useful applications. This study was conducted as part of a tag and release study of greater amberjack in the Gulf of Mexico (D. Murie and D. Parkyn University of Florida, unpublished data) and the non lethal data on sex obtained from this study are being used to elucidate information on sex specific migration patterns, growth rates, and mortality rates as tagged fish are recaptured. Additionally, th e celerity of this method (< 1 minute per fish in most cases), its simplicity, and the minimal training required, makes it a suitable candidate for obtaining sex data from greater amberjack by on board observers as well as port samplers, which generally ne ed to use methods

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45 that allow for relatively rapid data collection that do not require a great deal of technical skill (G. Fitzhugh, National Marine Fisheries Service, personal communication). As with greater amberjack, tagging studies of other species cou ld benefit from sex data that is currently unavailable. Within the Gulf, cobia Rachycentron canadum has been a species at the focus of several large tagging studies (Franks et al. 1991; Burns and Neidig 1992; Hendon et al. 2008 ) but currently there is no means to differentiate their sex externally. Large pelagic species such as marlin ( Istiophoridae ) swordfish Xiphias gladius and bluefin tuna Thunnus thynnus are often tagged with internal archival or pop off archival tags, but sexing data are generally u navailable (Block et al. 1998, 2005; Bridges et al. 2000; De Metrio et al. 2002). A method using steroid, hormone, and protein levels of muscle biopsy samples has been developed to sex swordfish and bluefin tuna that are landed either gutted or whole, but these fishes are too economically valuable for invasive samples to be taken (Bridges et al. 2000). However, as discussed previously, methods relying on concentrations of these indicators can be costly and may have decreased accuracies in immature individua ls and outside of the reproductive season (Martin et al. 1983; Blythe et al. 1994; Martin Robichaud and Rommens 2001; Moghim et al. 2002; Colombo et al. 2004). If the use of urogenital pore characters could be adapted for large pelagic species, such as the se, it could allow for the sexing of at least some of these species in conjunction with tagging studies. In particular, bluefin tuna are often brought aboard a vessel for tagging (Block et al. 1998, 2005; Metrio et al. 2002), which would allow for the use of such a non lethal sexing method. These are just a few examples of species that may benefit from an attempt to use this non lethal sexing method. Tagging studies on any fish species would benefit from prior knowledge of sex, which may be useful in determ ination of sex specific migration, growth, and mortality. These data are generally unavailable if it is not obtained at the time of

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46 tagging due to the paucity of tag returns with accompanying sex information and the potential for misidentification by those who have recaptured the fish (St Pierre 1992; D. Murie and D. Parkyn, University of Florida, unpublished data). The ability to non lethally sex greater amberjack has also provided an alternative means to estimate sex ratios from fish as small as 534 mm, not just those large enough to land in the fisheries. This can be used in conjunction with sex ratios obtained from more traditional methods, such as port sampling of the landed catch, to provide a range of reasonable values that should be considered in th e management of this species. The only pr eviously published overall sex ratio for greater amberjack in the Gulf of Mexico was estimated as 0.4 males to 1 female (Thompson et al. 1999) Sex ratio estimates from the Murie and Parkyn (2008) dataset, both over all and annual, indicated a similar degree of female skewing in the sex ratio. Sex ratios calculated from the non lethal sexing data for fish from both the Gulf of Mexico and the US South Atlantic however, show ed minor male skewing. These were similar to sex ratios obtained by Harris et al. (2007) in the US South Atlantic, as well as to a value of 1:1, which is currently the assumed sex ratio for assessments of the Gulf stock (NMFS 2006). None of the overall sex ratio findings from this study showed the mo derately high, male skewing that was observed by Burch (1979). The overall male skewing observed by Burch may have arisen, in part, due the time of year and location of his samples. All of the samples collected by Burch were individuals collected from char ter boat landing from a single port, with a large number of the samples collected in during three consecutive months. Preliminary analysis of site specific sex ratios from data collected for Gulf of Mexico greater amberjack (Murie and Parkyn 2008; D. Murie and D. Parkyn, University of Florida, unpublished data) has shown that particular geographic locations may have largely skewed (male or female) sex ratios during at least some times during the year

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47 (personal observation). For instance, site specific sex r atios from fish collected offshore of Apalachicola, FL during March showed male skewing as large as 11:1 and a male skew for all locations in that region during that time of approximately 3:1 (G. Smith, University of Florida, thly sex ratio estimates show that during the time of year when most of his samples were collected males predominated; while during other months when fewer samples were collected the sex ratios could be near 1:1, male skewed, or female skewed. All previous ly published sex ratios for greater amberjack > 1 m FL from the Gulf of Mexico and the US South Atlantic as well as the results from this study indicate d that there wa s a relati vely large female skew (approximately 70% female) for this size class This l ends support to the notion that the commercial amberjack fishery, wi th a minimum size limit of 914 mm FL likely has a higher selectivity for female fish. The female skewing observed in these larger individuals could arise from faster growth rates that hav e been observed in female greater amberjack (Harris et al. 2007, Murie and Parkyn 2008), or it could be attributable to some other factor such as greater natural mortality of male greater amberjack. The female skewed sex ratio for fish <700 mm FL calculate d from the Murie and Parkyn (2008) dataset indicate d that if a female skew in the overall sex ratio does exist for Gulf of Mexico greater amberjack that it may be attributable to some other factor s naturally occurring or otherwise, than size selective fis hing alone since these fish were below the minimum size. However, the results for the same size class from non lethal sexing data show ed no indication of a sex ratio substantially different from the assumed 1:1 sex ratio. There were potential biases and er rors that may have occurred with both methods used to calculate sex ratios in this study. The majority of the Murie and Parkyn (2008) dataset contained samples obtained through port sampling. These p ort sampled fish may not accurately represent

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48 the true se x ratio of the stock because p ort sampled fish do not represent the entire catch, but only the portion of the catch that is brought to port. This provides no sex data for any of the discarded fish, and of those fish that are brought to port only a portion are sampled for sex data. In addition, there is little representation from the commercial fishery due to gutting of the fish at sea. There could also be a potential bias in sexes for landed fish due to the size limits imposed on the fishery, since females are in general larger at age and are also predominant in the large st size classes. The use of non lethal sexing in conjunction with a tag and release study has provided an alternative method of obtaining sex ratios, which can alleviate some potential bias es by allowing sampl es to be collected for the entire catch However, there are limitations to this method as well There is a potential for bias in the overall sex ratio due to highly skewed sex ratios at individual sites skewing the entire dataset. As me ntioned above, preliminary analysis of sex ratios for individual sites has indicated that the sex ratio for a particular location can be highly skewed towards one sex or the other (G. Smith, University of Florida, unpublished data). There were no clear spa tial or temporal patterns in these site specific sex ratios that would create a particular bias in sampling a specific location or during a specific time of year, but this possibility cannot be ruled out without further sampling. The differences observed i n the Parkyn (2008) dataset and the non lethal sexing data may have arisen in part due to the potential biases discussed above for each method or possibly due to tem poral changes in the sex ratios. Differences in the sex ratios for fish <700 mm FL may have arisen in part due to site specific or regional skewing of sex ratios. A large number of fish from this size class in the Murie and Parkyn (2008) dataset were obtai ned from several locations off the coast of Suwannee, FL,

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49 which often showed site specific female skewing (G. Smith, University of Florida, unpublished data). This may have lead to the female skewing observed in the sex ratio for this size class from their dataset. Large numbers of fish in this size class from the non lethal sexing data were obtained from several areas of the Florida coast with different degrees of site specific skewing in the sex ratios. Both male and female site specific skewing were obse rved off Madeira Beach, female skewing was observed off Suwannee, and male skewing was observed off of Apalachicola (G. Smith, University of Florida, unpublished data), resulting in an overall unskewed sex ratio for this size class from non lethal sexing. Even with the potential shortcomings found in the different methods used to obtain sex data, it is likely that the sex ratios calculated would at least represent a range of likely values that should be considered in the assessment of this stock.

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50 Table 2 1. Summary of non lethal sexing methods used for a variety of fish species. The type of reproductive information obtained from each study is indicated by an X or the accuracy (%) reported Method Species Common name Sex Maturation status a Reference Ster oid, hormone, Acipenser transmontanus White sturgeon 85 100 72 100 Webb et al. 2002 and protein levels Acipenser transmontanus White sturgeon X Feist et al. 2004 Epinephelus guttatus Red hind X Heppell and Sullivan 1999 Epinephelus striatus Nassa u grouper X Heppell and Sullivan 1999 Gadus morhua Atlantic cod 94 100 Sangalang 1978 Mycteroperca microlepis Gag X X Heppell and Sullivan 1999 Mycteroperca microlepis Gag X X Heppell and Sullivan 2000 Oncorhynchus mykiss Rainbow trout 86 100 Sangalang 1978 Oncorhynchus mykiss Rainbow trout X Evans et al. 2004 Oncorhyrnchus kisutch Coho salmon X Gordon et al. 1984 Parophrys vetulus English sole 68 70 Johnson and Casillas 1991 Salmo salar Atlantic salmon X Le Bail and Breton 1981 S almo salar Atlantic salmon X Evans et al. 2004 Salmo trutta fario Brown trout X Le Bail and Breton 1981 Salvelinis fontinalis Brook trout 93 100 Sangalang 1978 Seriola dumerili Greater amberjack X Takemura et al. 1996 Palpation Oncorhync hus masou masou Masu salmon X Kano 2005 Oncorhynchus mykiss Rainbow trout X Kano 2005 Salvelinus leucomaenis leucomaenis White spotted char 96 Kano 2005 a Maturation status may include immature vs. mature, pre spawn vs. post spawn, and/o r reproductive stage. b Fecundity also estimated. c Denotes a study in which a number of methods associated with external urogenital features was investigated

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51 Table 2 1. Continued. Method Species Common name Sex Maturation status Reference Surgical b iopsy Acipenser oxyrhincus desotoi Gulf sturgeon X X Parkyn et al. 2006 Epiephelus merra Honeycomb grouper 100 100 Alam and Nakamura 2008 Morone saxatilis Striped bass 95 Ritchie 1965 Endoscopy Acipenser brevirostrum Shortnose sturgeon X K ynard and Kieffer 2002 Micropterus salmoides Largemouth bass 97 Driscoll 1969 Oncorhynchus mykiss Rainbow trout X X Moccia et al. 1984 Salvelinis fontinalis Brook trout 96 96 Swenson et al. 2007 Salvelinus alpinus Arctic charr X X Ortenburger et a l. 1996 Scaphirhynchus albus Pallid sturgeon X Wildhaber et al. 2005 Scaphirhynchus albus Pallid sturgeon X Bryan et al. 2007 Scaphirhynchus platorynchus Shovelnose sturgeon 75 93 Wildhaber et al. 2005 Scaphirhynchus platorynchus Shovelnos e sturgeon X Bryan et al. 2007 Ultrasound Oncorhyrnchus kisutch Coho salmon X Martin et al. 1983 Imaging Acipenser stellatus Stellate sturgeon 97 X Moghim et al. 2002 Clupea harengus pallasi Pacific herring X Bonar et al. 1989 Epinephel us guttatus Red hind X b Whiteman et al. 2005 Gadus morhua Atlantic cod X Karlsen and Holm 1994 Hippoglossus hippoglossus Atlantic halibut X Shields et al. 1993 Hippoglossus hippoglossus Atlantic halibut X X Martin Robichaud and Rommens 20 01

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52 Table 2 1. Continued. Method Species Common name Sex Maturation status Reference Ultrasound imaging Ictalurus furcatus X I. punctatus Hybrid catfish 80 100 X Burtle et al. 2003 Maccullochella peelii peelii Murray cod 96 X Newman et al. 2008 Melanogrammus aeglefinus Haddock X X Martin Robichaud and Rommens 2001 Morone saxatilis Striped bass 95 99 X Blythe et al. 1994 Morone saxatilis Striped bass X b Will et al. 2002 Morone saxatilis Striped bass X b Jennings et al. 2005 Moron e saxatlis X M. chrysops Hybrid striped bass 42 100 Blythe et al. 1994 Noturus placidus Neosho madtom X X b Bryan et al. 2005 Oncorhynchus mykiss Rainbow trout X X Reimers et al. 1987 Oncorhynchus mykiss Rainbow trout X X Evans et al. 2004 Pleur onectes americanus Winter flounder X Martin Robichaud and Rommens 2001 Pleuronectes ferruginea Yellowtail flounder X Martin Robichaud and Rommens 2001 Salmo salar Atlantic salmon X X Reimers et al. 1987 Salmo salar Atlantic salmon X Mattson 1991 Scaphirhynchus albus Pallid sturgeon X Wildhaber et al. 2005 Scaphirhynchus platorynchus Shovelnose sturgeon 86 Colombo et al. 2004 Scaphirhynchus platorynchus Shovelnose sturgeon 59 76 Wildhaber et al. 2005

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53 Table 2 1. Continued. M ethod Species Common name Sex Maturation status Reference Ultrasound imaging Scaphirhynchus platorynchus Shovelnose sturgeon X b Bryan et al. 2007 Verasper moseri Barfin flounder X Matsubara et al. 1999 Urogenital Acanthuridae Surgeonfis hes X Ross 1984 catheterization Barbodes schwanenfeldi Tinfoil barb X Bailey and Cole 1999 Centropomus medius Blackfin snook X Alvarez Lajonchre et al. 2001 Centropomus parallelus Fat snook X Ferraz et al. 2004 Chaetodontidae Butterflyfish es X Ross 1984 Dicentrarchus labrax European sea bass X Asturiano et al. 2003 Dicentrarchus labrax European sea bass X Mylonas et al. 2003 Epinephelus marginatus Dusky grouper X Marino et al 2003 Epinephelus rivulatus Halfmoon grouper 80 96 Mackie 2000, 2003 Labridae Wrasses X Ross 1984 Lates calcarifer Barramundi X Garcia 1989 Mugil cephalus Striped mullet X Shehadeh et al. 1972 Scophthalmus maximus Turbot X McEvoy 1983 Seriola dumerili Greater amberjack X Seriola dumerili Greater amberjack X Mylonas et al. 2004 Tilapia zillii Redbelly tilapia X Coward and Bromage 2001 External urogenital Acipenser spp. Sturgeon 82 Vecsei et al. 2003 features Ambloplites rupestris Rock ba ss 65 98 Noltie 1985 Esox lucius Northern pike 91 94 Casselman 1974 Hippoglossus stenolepis Pacific halibut 98 St Pierre 1992

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54 Table 2 1. Continued. Method Species Common name Sex Maturation status Reference External urogenital Ictalurus punctatus Channel catfish 99 Norton et al. 1976 features Lepomis macrochirus Bluegill 100 McComish 1968 Micropterus salmoides Largemouth bass 51 92 Parker 1971 Micropterus salmoides Largemouth bass X Manns and Whiteside 1979 Micropterus salmoides Larg emouth bass 48 94 c Benz and Jacobs 1986 Morone chrysops White bass X Sigler 1948 Oreochromis spp. Tilapia X Popma and Masser 1999 Sarotherodon spp. Tilapia X Popma and Masser 1999 Sebastes paucispinis Boccacio X Moser 1967 Sebastes caurinus Copper rockfish X Murie 1991 Sebastes maliger Quillback rockfish X Murie 1991 Tilapia spp. Tilapia X Rakocy and McGinty 1989 Tilapia spp. Tilapia X Popma and Masser 1999

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55 Table 2 2. Maturation stages of greater amberjack based on general app earance of oocytes from catheter samples following descriptions by Grau et al. (1996), Micale et al. (1999), Poortenaar et al. (2001), and Harris et al. (2004, 2007). Maturation Stage Defining oocyte type Oocyte stages present Immature/resting Primary gr owth Stages up to late perinucleous stage Early developing Early developing Stages up to cortical alveolus stage Late developing Late developing Stages up to yolk granule Ripe Hydrated or late developing and degraded Stages up to yolk granule and hydrat ed and/or degraded oocytes Spent Early developing and degraded Stages up to cortical alveolus stage and degraded oocytes, but no yolk granule or hydrated oocytes

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56 Table 2 3. Number of catheterized fe male greater amberjack classified into each maturation stage described in Table 2 2 by month. Maturation Stage Total March April May June November Immature/Resting 21 13 6 0 1 1 Early Developing 5 3 2 0 0 0 Late Developing 23 4 14 5 0 0 Ripe/Running 42 0 25 17 0 0 Spent 1 0 1 0 0 0

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57 Table 2 4. Number of catheterized female greater amberjack classified into each maturation stage described in Table 2 2 by 100 mm FL size class. Maturation Stage Total 500 600 700 800 900 1000 1100 1200 1300 1400 Immature/Resting 21 5 4 6 5 1 0 0 0 0 0 Early Devel oping 5 0 0 0 2 2 1 0 0 0 0 Late Developing 23 0 0 0 0 3 11 5 4 0 0 Ripe/Running 42 0 0 0 2 7 20 5 7 1 1 Spent 1 0 0 1 0 0 0 0 0 0 0

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58 Table 2 5 Overall sex ratios, sex ratios for individuals <700 mm fork length (FL), sex ratios for individuals amberjack in the Gulf of Mexico and US South Atlantic. Group Sex ratio (m:f) Sample size Source Gulf of Mexico Overall 0.4:1 351 Thompson et al. 1999 0.59:1 1526 Murie and Pa rkyn 2008 dataset (This study) 1.19:1 258 Non lethal sexing (This study) <700 mm FL 0.72:1 293 Murie and Parkyn 2008 dataset (This study) 1.18:1 48 Non lethal sexing (This study) 0.56:1 1233 Murie and Parkyn 2008 dataset (T his study) 1.19:1 210 Non lethal sexing (This study) 0.39:1 173 Beasley 1993/Thompson et al. 1999 0.47:1 202 Murie and Parkyn 2008 dataset (This study) 0.43:1 10 Non lethal sexing (This study) US South Atlantic Overall 1.5:1 1202 Burch 1979 0.9:1 2206 Harris et al. 2007 1.07:1 176 Non lethal sexing (This study) 1.07:1 176 Non lethal sexing (This study) 0.52:1 882 Harris et al. 2007 0.49:1 102 Non lethal sexing (This study)

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59 Figure 2 1. Catheter used to obtain milt and oocyte samples from greater amberjack. Phot o courtesy of Geoffrey H. Smith Jr. Photo by G. Smith

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60 Figure 2 2. Male urogenital region of greater amberjack with anus, genital pore, and urinary pore denoted. The urinary pore is the most posterior structure. A) Genital and urinary pores are both clearly visible in this specimen. B) The urinary pore is partially covered by a septum between the genital and urinary pores in this specimen. Note that the septum is approximately 1 mm in width. Phot o s courtesy of Geoffrey H. Smith Jr. B A Photo by G. Smith Photo by G. Smith

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61 F igure 2 3. Female urogenital region of greater amberjack with anus, genital pore, and urinary pore denoted. The urinary pore is the most posteriour structure. A) Septum is greater than 1 mm in width and white in color in this specimen. Some of the papilla like tissue surrounding the pores is beginning to extend between them. B) Urinary pore is located slightly off the midline in this specimen. Phot o s courtesy of Geoffrey H. Smith Jr. B A Photo by G. Smith Photo by G. Smith

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62 Figure 2 4. Urogenital region of a reproductively active female greater amberjack with the anus, genital pore, and urinary pore denoted. The urinary pore is the most posterior structure. The genital pore is enlarged and crescent shaped, and the papilla like tissue surrounding the pores has extended between them. Phot o courtesy of Geoffrey H. Smith Jr. Photo by G. Smith

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63 Figure 2 5. Numbers of greater amberjack non lethal ly sexed and numbers of greater amberjack that had their sex verified by milt expression, urogenital catheterization, or disssection of sacrificed fish.

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64 Figure 2 6. Number of female and male greater amberjack non lethally sexed by size class with s ex verified by milt expression, urogenital catheterization, or disssection of sacrificed fish. A) B )

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65 Figure 2 7. Percent accuracy of non lethal sexing of greater amberjack by size class using features of their urogenital pores. Sample sizes are given above t he respective bars for each size class.

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66 Figure 2 8. Representative images of greater amberjack oocytes at various stages of maturity collected via urogenitalcatheterization: A) female classified as immature or restin g (only primary oocytes visible = P); B) female classified as early developing (oocytes up to cortical alveolus stage present = ED); C) female classified as ripe (contains fully hydrated oocytes = H, yolk granule stages are also present = LD); D) female cl assified as spent (with degraded oocytes = D, but no yolk granule or hydrated oocytes). Scale bar in all images is 0.5 mm. Phot o s courtesy of Geoffrey H. Smith Jr. P ED P B A C D P ED LD H ED D Photo by G. Smith Photo by G. Smith Pho to by G. Smith Photo by G. Smith

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67 Figu re 2 9. Mean oocyte diamter of each oocyte type obtained from urogenital catheter samples of greater amberjack following de scr iptions given in Table 2 2. Mean oocyte diameters were calculated for each fish for each oocyte type present in the sample and then averaged among fish in which a particular type of oocyte was measured. Error bars represent the standard error of the mean diameter of each oocyte type, with number of fish sampled given above error bars

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68 Figure 2 10. Annual male to female sex ratios from the Murie and Parkyn (2008) dataset for 2002 2008. The solid line represents the mean and the dashed line represent s the median (2nd quartile). Upper and lower ends of the box represent the 1st and 3rd quartiles, respectively. Whiskers represent the upper and lower range of values observed on an annual basis. Sex Ratio (males : female)

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69 CHAPTER 3 SEX RATIO EFFECTS ON POPULATION DYNAMICS OF GREATE R AMBERJACK Overview Traditionally, fisheries models tend to focus on growth, reproduction, and survival of a population, with little consideration of behavior, life history strategies, and reproductive patterns. However, there is an increasing realization that proper management requires an understanding of these factors, as well as growth, reproduction, and survival (Alonzo and Mangel 2004, 2005). Gonochoristic, as well as sex changing, populations tend to have a reduced reproductive capacity as fishing in creases due to a decrease in stock biomass and resultant decrease in reproductive individuals (Huntsman and Schaaf 1994). In sex changing species that undergo size selective fishing there tends to be a large reduction in the individuals of the larger sex. This leads to an altered sex ratio and a theoretical reduction in reproductive potential either through egg or sperm limitation, which is often predicted to be greater than that seen in gonochoristic species if there is no compensation mechanism (Huntsman and Schaaf 1994; Armsworth 2001; Alonzo and Mangel 2004, 2005; Heppell et al. 2006; Molloy et al. 2007; Alonzo et al. 2008; Brooks et al. 2008). In protogynous species, including gag grouper Mycteroperca microlepis grasby Epinephelus cruentatus coral tr out Plectropomus leopardus and California sheepshead Semicossyphus pulcher models have been developed that incorporate sex ratio and fertility rates in determining recruitment based on the number of fertilized eggs rather than simply the total number of eggs produced, in order to incorporate the potential for sperm limitation (Huntsman and Shaaf 1994; Armsworth 2001; Alonzo and Mangel 2004, 2005; Heppell et al. 2006; Alonzo et al. 2008; Brooks et al. 2008). The ability to estimate biological reference poi nts in protogynous species can be based on female spawning biomass, male spawning biomass, and

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70 total spawning biomass. If the potential for decreased fertilization is weak, female spawning biomass will provide the most accurate estimates. Male spawning bio mass will provide the most accurate estimates if the potential is very strong, and total spawning biomass will provide the most accurate estimates if the potential is moderate or unknown (Brooks et al. 2008). In protogynous species, female spawning biomass and total spawning biomass consistently produced relative errors in opposite directions over the range of fertilization rates that were considered probable. This occurs because female spawning biomass never accounts for reduction in fertilization success, while total spawning biomass always does. This theoretically creates a situation where female spawning biomass tends to overestimate the productivity of a stock, while total biomass tends to provide a more conservative effort. This would allow for the use of these two different biomass estimates to bound uncertainty in reference points (Brooks et al. 2008). When all male size classes of a protogynous species are fished, a population will theoretically see greatly reduced recruitment and in many cases the p otential for a population crash, but if some male size classes escape fishing, and fertility rates are relatively high, then the potential for a crash is greatly reduced (Alonzo and Mangel 2004; 2005). In populations where a compensation mechanism occurs, such as plasticity in the size at sex change, then these populations may be as resilient as those of a gonochoristic species (Huntsman and Schaaf 1994; Heppell et al. 2006). The greater reduction in reproductive output in protogynous species compared to go nochoristic species may not apply to all levels of fishing mortality as they are not inherently more susceptible to exploitation (Brooks et al. 2008). Protandry is less common than protogyny in fishes, but there are a number of targeted species such as bar ramundi Lates calcarifer snook, Centropomus spp and shads Tenualosa spp. that exhibit this form of sex change (Molloy et al. 2007). The potential for egg limitation due to

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71 size selective fishing exists for these species, but has generally not been incor porated into models. Fu et al. (2001) predicted that a protandrous shrimp Pandalus spp. would be more vulnerable to recruitment overfishing than hypothetical non sex changing populations if there were no plasticity in size at sex change. Molloy et al. (200 7) employed a similar model to those used for protogynous species incorporating sex ratio and fertilization rates to look at the number of fertilized eggs as an indication of recruitment in protandrous species, with white seabream Diplodus sargus as a mode l species. As with protogynous fish, there is, theoretically, a marked reduction in recruitment in size selective fisheries, in this case due to egg limitation rather than sperm limitation. This effect can be amplified if pre sex change individuals, as wel l as all size classes of post sex change individuals, are subjected to fishing pressure because few if any individuals will survive to sex change to replace the females being removed (Molloy et al. 2007). Again, as with protogynous species, a population ma y be as resilient as a gonochoristic one if there is some compensatory mechanism to increase reproductive output (Molloy et al. 2007). The need to understand the effect of males on reproductive output is not limited to protogynous species, as any species i n which fishing imposes greater mortality on males than on females may have similar affects (Alonzo et al. 2008), and it is likely that the same would apply to species in which females undergo greater fishing mortality than males. Greater amberjack are not a sex changing species but the potential exists for differential exploitation of one sex over the other due to size selective fisheries and evidence of potential sex ratio skewing (Chapter 2). Greater amberjack are gonochoristic, but show sexual dimorphis m in growth with females generally being larger than males at age as well as dominating the largest size classes However, this greater growth of females than males at a specific age appears to be less significant in the Gulf of Mexico stock (Murie and Pa rkyn 2008) compared to the US South Atlantic stock (Harris

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72 et al. 2007), but may still play some role in creating a sex selective fishery due to size regulations. Minimum size limits make both t he recreational and commercial fisheries in the Gulf of Mexico size selective (762 mm FL (30 in) and 914 mm FL (36 in), respectively, in 2011). In addition, because of an increased minimum size regulation for the commercial fishery, it selects for larger fish, which may consist mostly of females since fish > 1 m FL a ppear to be comprised of approximately 70% females in both the Gulf of Mexico and US South Atlantic stocks (Chapter 2). Factors other than faster growth rates in females may contribute to this female skewing, as the differences in growth rates between sexe s was less apparent in the Gulf stock, but there was still evidence for female skewing in these largest size classes. The recreational fishery tends to select fish over 762 mm FL (due to current size regulations), but may have a truncated selectivity of la rger fish due to gear limitations, such as line break offs of larger fish, and travel limitations, such as leaving the larger fish out of reach of anglers on day trips due to their location further offshore, which may possibly lead to more males being harv ested. Some preliminary data indicate that site specific sex ratios of greater amberjack can be highly skewed to one sex or the other ( G. Smith, University of Florida, unpublished data ), which could be another contributing factor that may lead to sex selec tive fisheries in the Gulf stock of greater amberjack. The overall goal of this study was to examine the effects of sex ratios on the population dynamics of greater amberjack in the Gulf of Mexico. The specific objectives were to apply estimated sex ratios (Chapter 2) to a sex, size and age structured population model to 1) determine the effects of male and female skewed sex ratios on the reproductive potential of the stock, and 2) estimate the effect on parameters of reproductive output from size selectiv e fishing on females > 1m FL.

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73 Methods A two sex, size and age structured model was constructed to examine the potential impacts of both male and female skewed sex ratios on the reproductive potential of the Gulf of Mexico greater amberjack stock by exam ining a number of output parameters measuring both male and female contributions to the reproductive potential of the stock. Qualitatively, output parameters that were driven to zero in model simulations were considered to be indicative of a stock collapse Other possible outcomes for output parameters included a continual decline towards zero, and reaching equilibriums at various levels. Models were run for 50 years with no fishing mortality for the model to equilibrate, and subsequently 50 years of fishi ng mortality was applied. Measures of the impact of skewed sex ratios and fishing on reproductive potential included female sp awning stock biomass male sp awning stock biomass total fecun dity (egg production) fertili ty (sperm production ), and fertilized egg production. Both spawning potential ratio (SPR) and weighted spawning potential ratio (wSPR) were calculated, as these are measures that are often used to evaluate if recruitment overfishing is occurring (Mace and Sissenwine 1993; Mace et al. 1996). Sp awning potential ratio is defined as the ratio of some measure of productivity on a per recruit basis in the fished to the unfished condition (Goodyear 1990). Weighted spawning potential ratio is defined as ratio of total annual egg production in the fishe d to the unfished condition (Mace et al. 1996). Greater weight is placed on recruitment in wSPR than SPR, which is mainly influenced by mortality (Mace et al. 1996; NMFS 1996). For this study SPR, was measured as the ratio of fertilized eggs per recruit in the fished condition to the number of fertilized eggs per recruit in the unfished condition, and wSPR was measured as the ratio of the number of fertilized eggs in the fished condition to the number of fertilized eggs in the unfished condition to incorpor ate both

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74 male and female contributions to the productivity of the stock. The average across 100 simulations was calculated for each of these values. Models were run with varying sex ratios applied either at the level of recruitment or based on size. Model s with sex ratios applied at recruitment were used to examine the effects of different sex ratios were applied in these models. A sex ratio of 1:1 was used as a base case scenario as this is the sex ratio that was assumed in the most recent stock assessment (NMFS 2006 ). Several of the overall sex ratio estimates from Chapter 2 also fell near 1:1. Male to female sex ratios of 2:3 and 1:2 were modeled based on the f indings of the sex ratio analyses of Gulf of Mexico greater amberjack ( Chapter 2 ) Male to female sex ratios of 1:3 and 1:5 were also examined as more extreme cases of sex ratio skewing Skewing of sex ratios to this degree was not observed in estimates of the overall sex ratio (Chapter 2), however, site specific sex ratios commonly showed skewing to this degree and in some cases to a greater degree ( up to 11:1 in some cases; G. Smith, University of Florida, unpub lished data). The reciprocal value of all of these sex ratios (3:2, 2:1, 3:1, and 5:1) were also analyzed to examine the potential effects of male skewed sex ratios on reproductive potential. Size based sex ratios were applied in two different ways. One set of size based sex ratio models was used to examine the effects of sex ratios that may have arisen from fishing due to possible sex selectivity in the Gulf of Mexico greater amberjack fisheries, arising from potential geographic skewing of sex ratios and the size selective nature of these fisheries Greater amberjack in the Gulf of Mexico reach the minimum recreational size limit over a range of ages due to variability in their growth rates. However, to simplify model calculations, the sex ratios were applied at age three, which is the age at which the von Bertalanffy growth curve (Murie and

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75 Parkyn 2008) predicts Gulf of Mexico greater amberjack to exceed the current recreational size limit (762 mm FL) for both sexes. This is also the age at which the von Bertanlanffy growth curve (Murie and Parkyn 2 008) predicts that both sexes will exceed 700 mm, which was the cut used to calculate the sex ratios being modeled (Chapter 2). For these models, the sex ratio was assumed to be 1:1 prior to fishing (the first 50 years of the model) and below age three. Fr om age three onward, the sex ratios described above for the previous set of models were applied. The second set of size based sex ratio models involved a single 0.43:1 female skewed sex ratio (i.e., 1 male to 2.3 females), which was applied to fish > 1 m FL. This sex ratio was used to represent the female skewing (approximately 70% females) observed in the sex ratio analysis of fish > 1 m FL (Chapter 2). As with the previous model, a knife edge age, rather than a stepped representation of the age at which fish would reach a specific length (1 m FL for this set of models), was used to simplify model calculations. The corresponding age at which both male and females were predicted to be closest to 1 m FL by the von Bertanlanffy growth curve for the Gulf stock was age 5 (Murie and Parkyn 2008). The female skewed sex ratio was thus applied at age 5 and onward. In this set of models, the sex ratio was applied both prior to and after the start of fishing to examine how female skewing of large individuals could inf luence productivity in relation to the the 1:1 sex ratio, and how fishing could influence any differences that may exist. The sex ratio for fish < 1 m was assumed to be 1:1 for comparison with the sex ratio that was assumed in the most recent stock assessm ent. For models with sex ratios applied based on size/age, the number of males and females were bounded such that when the sex ratio was applied the number of males and females of a specific age in a specific year did not exceed the corresponding number of males or females 1 yr less in age for the previous year.

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76 Estimates of the current instantaneous fishing mortality rate ( F ) for greater amberjack in the Gulf of Mexico from the Assessment Workshop of the 2006 Gulf of Mexico greater amberjack stock assess ment, covered a range of 0.21 0.60 (NMFS 2006). The model preferred by the Assessment Workshop estimated the current F to be 0.49 (NMFS 2006). To cover this range of values without exceeding it, a base case scenario F value of 0.4 was selected and F value s 20% in either direction (0.2 and 0.6) were selected as alternative values The Review Workshop for the 2006 Gulf of Mexico stock assessment preferred a different model provided in an addendum, which estimated the current F to be 0.86 (NMFS 2006). However, some preliminary model runs indicated probable stock collapses regardless of the sex ratio applied, making any comparisons based on sex ratios impossible. To incorporate the sex specific growth rates present in greater amberjack, von Bertalanffy growth p arameters for each sex (Table 3 1) were used to determine length at age for model scenarios with sex ratios applied at recruitment. The growth model was parameterized as: L t = L (1 e k ( t t o ) ) (3 1) where L t is FL (mm) at time t L is the asymptotic FL (mm), k is the growth coefficient, and t o is the hypothetical age at zero length. In models with sex ratios applied at recruitment, separate growth and mortality sche dules were applied to each sex, as the sex ratio was applied before any mortality has been modeled. For models varying sex ratio based on size, separate growth and mortality schedules for each sex could not be applied at the same time that a sex ratio was being applied at a specific age/size. Doing so would create a circular loop in the model calculations. To apply the various sex ratio scenarios, a single von Bertalanffy growth curve was used for both sex (Table 3 1). This most likely resulted in some loss in the ability to model differences in mortality rates for males and females arising from different growth rates for each

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77 sex. However, the sex ratios applied in the first set of size based models were themselves intended to represent sex selective mortal ity arising from size selective fisheries or sex selectivity arising from other factors, such as geographically specific sex skewing. The difference in growth between males and females for the Gulf stock was also relatively small, making the loss of inform ation from using a single growth curve minimal. The weight at length relationship for males and females was described by: WT = a FL b (3 2) where WT is the whole weight (kg), and a and b are constants in the length weight relatio nship (Table 3 1) The weight at length relationships for males and females were pooled because Murie and Parkyn (2008) found no significant difference between the sexes. The number of fish at age a and time t in the unfished condition (for each sex) was determined as: N a, t = N a 1 ,t 1 e M (3 3) where: N a,t is the number of fish at age a and time t N a 1 t 1 is the number of fish of the previous age in the previous year, and M = instantaneous natural mortality rate. A value of M equal to 0.25 was used based on the baseline value used in the 2006 Gulf of Mexico Stock Assessment (NMFS 2006) (Table 3 1). The number of fish at age a and time t in the fished condition (for each sex) was calculated as: N a,t = N a 1 ,t 1 e M [(1 U HL t 1 *( P cl + (1 P cl ) D )) ( 1 U LL t 1 ( P cl + (1 P cl ) D )) (1 U HB t 1 ( P rl + (1 P rl ) D )) (1 U CBPB t 1 ) ( P rl + (1 P rl ) D )] (3 4)

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78 where: U is the annual exploitation rate ( U = ( F (1 e Z ) ) / Z ), where F = instantaneous fis hing mortality rate and Z = instantaneous total mortality rate, and Z = F + M ; HL, LL, HB, and CBPB are the gear selectivities for commercial handline gear, commercial longline gear, recreational headboat fishery, and the combined charter and private boat recreational fishery respectively (Table 3 2); D = discard mortality applied across all ages and fisheries (Table 3 1); P cl and P rl = the proportion of fish at age that are of legal size for the commercial and recreational fisheries, respectively ( P cl/rl = 1 / (1 + e ( ( L t M SL) / ) where M SL is the commercial or recreational minimum at often set at 10% of a particular length of interest, in this case MSL (Coggins et al. 2007; Pine et al. 2008; Tetzlaff et al. 2011). The ratios of the difference in the upper and lower estimates of length at age estimates and mean length at age estimates for Gulf of Mexico greater amberjack, which were calculated from mean values and standard errors of von Bertalanffy growth parameters from Murie and Parkyn (2008), ranged from approximately 0.05 to 0.13. Based on this information, incorporate the difference in size at age between males and females. The number of mature males and females ( N mat ) for each year was calculated as: N mat a N a t P mat where: P mat is the proportion mature at age a for each sex based on Table 3 3. Male and female spawning stock biomass (SSB) f or each year was calculated as: a N mat WT, where WT = whole weight (in kg) at age a Batch fecundity at age ( BF a ) was calculated as: BF a = a f + ( b f Age), where a f and b f are constants in the fecundity age relationship (Table 3 1) Annual fecundity at age ( AF a ) was calculated as AF a = n BF a where n = number of spawnings per season (Table 3 1) The total

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79 number of eggs produced e ach year ( EP ) was determined by E P a NF a t AF a where NF a t = number of females at age a for each year There is little empirical data on male reproductive parameters in fisheries, which may necessitate the use of theoretical estimates for parameters related to male productivity (Trip pel 2003). Sperm production at age ( SP a ) wa s predicted to be much greater than egg production, and was therefore estimated to be 1000 times greater than egg production (SP a = 1000 AF a ) (Alonzo and Mangel 2004 ; Molloy et al. 2007) Total annual sperm prod uction ( SP ) was determined by S P a NM a,t SP a where NM a,t = number of males at age a for each year. The proportion of fertilized eggs ( P fegg ), which wa s a function of the fertilization rate and the proportion of mature males in the spawning stock was estimated as: P fegg = f max (1 e P male ) (from Heppell et al. 2006), where: f max is the maximum fertilization rate; is a fertility parameter that determines the steepness of the curve; and P male is the proportion of mature males in the spawning stock, calculated as P male = N mat( male) / (N mat(male) + N mat(female) ). The maximum fertilization rate was set at 0.8 based on data from captive spawning experiments with greater amberjack by Jerez et al (2006); this was the highest average monthly fertilization rate observed in the study There is currently no empirical data on fertility functions in greater amberjack, thus would show essentially no changes in fertilization rate with the sex ratios modeled in this study, east minor changes in fertilization rate as the sex ratio varies, allowing for investigation of possible sperm limitation in highly female skewed sex ratios. Total annual production of fertilized eggs ( FEP ) was calculated as: FEP = EP P fegg

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80 In the 2006 stock assessment (NMFS 2006), recruitment was modeled using a hockey stick recruitment function (Barrowman and Meyers 2000). However, it was not possible to convert the parameters used in the hockey stick recruitment function, which were based on spawning stock biomass, to values that would correctly model recruitment based on fertilized egg production used in this study. Recruitment ( R t ) was therefore estimated using the compensation form of the Beverton and Holt model (Walters and Martell 2004, Catalano e t al. 2007) as: R t = ((recK / EPR 0 ) E t ) / (1 + ((recK 1) / ( R 0 EPR 0 )) E t ) (3 5) where: recK is the recruitment compensation ratio, which represents the ratio of juvenile survival in the unfished condition to juvenile survival in a state where le vels have been fished down to near zero ; and EPR 0 is the average unfished lifetime egg production per recruit This value wa s calculated by: EPR 0 a l a unfished AF a where l a unfished is the unfished survivorship at age a The unfished survivorship was calculated as the proportion of fish surviving from the previous year (starting at 1 for the first age modeled) multiplied by the unfished survival rate, S, whereS = e M Because recruitment in this model was being dictated by fertilized egg production in order to incorporate male and female contributions, FEPR 0 (average unfished lifetime fertilized egg production per recruit) was used in place of EPR 0 FEPR 0 was calculated as a l a unfished AF a P fegg E t (same as EP) was the number of eggs produced in year t again because recruitment in this model was being dictated by fertilized egg production, FE t (same as FEP ) was used in place of E t R 0 was average recruitment in an unf ished condition. To incorporate uncertainty in recruitment, a lognormal deviation was applied with a mean of 1 and coefficient of variation of 0.4 (Turner et al. 2000). A recK value of 10 was selected based on values from species with similar life historie s (Meyers et al. 1999) and from Goodwin et al. (2006) as: ln( recK ) = 4.69 + 0.32 ln( W ) + 0.72 ln( T mat ) 0.25 ln(Fec mat ) (3 6)

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81 where: W is the asymptotic total weight (estimated from Equation 3 2 for the maximum age modeled, age 10), T mat is the age where female maturity was 50% (estimated as 3.5 from Table 3 3), and Fec mat is the f ecundity at T mat (estimated by AF a at T mat ). Effects of sex ratio on reproductive potential were assessed by graphically comparing the mean values of FSSB, MSSB, EP, FEP, SPR, and wSPR from 100 simulations of each model permutation. Sensitivity analysis wa s performed on several input parameters, including discard mortality ( D ), both fertility parameters ( f max and ), recruitment compensation ratio ( recK ), and unfished recruitment ( R 0 ) (Table 3 1). These sensitivity analyses consisted of calculating the percent change in the mean value of 100 simulations for each output parameter in the final year of the model. Perc ent changes 10% from the base case scenarios ( F = 0.4 and 1:1 sex ratio for both models of sex ratios applied at recruitment and sex ratios based on size) were considered to be relevant and indicated that a particular parameter disproportionately influen ced output parameters requiring accurate estimation for reliable results. The discard mortality values used in the sensitivity analysis (0.0 and 0.4) were based on alternative values compared to D estimated in the 2006 stock assessment ( D = 0.2) (NMFS 2006 ). Values of 0.6 and 1.0 were used for the maximum fertilization rate, as 1.0 is the highest possible value and 0.6 was the average fertilization rate of greater amberjack observed by Jerez et al. (2006) in a captive setting. An chosen based on a theoretically high fertility value of 80 used by Heppell et al. (2006). The alternative values for unfished recruitment represent the upper and lower bounds of the 95% confidence interval for this parameter (300,000 and 400,000) (Diaz et al. 2005) Alternative values of recK were obtained from fish with similar life histories (Meyers et al. 1999) A value of 5 is among the lowest values reported for fish with similar life histories

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82 and a value of 15 represents an equivalent increase in rec K that is within the upper range of values reported for fish with similar life histories (Meyers et al. 1999). Results Modeling Effects of Sex Ratios Applied at Recruitment Male spawning stock biomass (MSSB) was highest, both prior to and after the start of fishing, in scenarios with the most highly male sk ewed sex ratio s, and decreased with decreasing male skew in the sex ratios for all values of F that were modeled (Figure 3 1 ) The proportion by which MSSB declined in the fished condition in relation to the unfished condition was the same regardless of the sex ratio, however, because of the different starting values the absolute changes in MSSB were much greater in male skewed than female skewed scenarios with the assumed 1:1 sex ratio falling in the mid dle (Figure 3 1). All sex ratios resulted in asymptotic values of MSSB for both an F of 0.2 and 0.4. In all cases the 1:1 sex ratio fell in between the extremes of the male and female skewed scenarios (Figure 3 1). As F increased the proportion by which M SSB declined in the unfished condition relative to the fished condition also increased, as would be expected, with an F of 0.6 resulting in values indicative of a stock collapse for the most female skewed scenarios. It was not clearly evident whether the r emaining sex ratio scenarios at this fishing pressure were slowly continuing to decline towards zero or if they had reached an equilibrium at a very low MSSB value (Figure 3 1C). Female spawning stock biomass (FSSB) showed a similar but reversed pattern to that of MSSB, with the highest values of FSSB occurring in the most female skewed sex ratios and declining as the sex ratio became more male dominated (Figure 3 2). Again, this occurred for all F values that were modeled. Like MSSB, the proportion of decl ine from the unfished to the fished condition was the same for all the sex ratios for a specific value of F but the absolute value of the decline increased with an increase in female skewing of the sex ratio. Increases in F

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83 values resulted in greater decl ines in the fished FSSB compared to the unfished FSSB. Equilibria were reached by all sex ratio scenarios for an F of 0.2 and 0.4, with the 1:1 sex ratio falling between the highest values seen in the female skewed scenarios and the lowest values seen in t he male skewed scenarios (Figure 3 2A and B). An F of 0.6 resulted in FSSB values indicating a stock collapse in the two most male skewed scenarios, while it was again difficult to discern whether the remaining sex ratio scenarios were continuing to slowly decline or whether they had reached an equilibrium at very low values (Figure 3 2C). Sperm production (SP) followed the same trends observed for MSSB with the greatest values, both prior to and after the onset of fishing in the model with the greatest male skewing in the sex ratio, and decreasing with increased female skewing of the sex ratio (Figure 3 3 ) An equilibrium was reached for all sex ratio scenarios for an F of 0.2 and 0.4 with the 1:1 scenario falling between the values for the male and fem ale skewed sex ratios (Figure 3 3A and B). As with the previous two output parameters, the proportion of decline from the unfished to the fished condition was the same for all sex ratio scenarios, but the absolute value of the decline increased with increa sed male skewing of the sex ratio. The decline from the unfished to fished condition also increased with an increase in the value of F with a value of 0.6 resulting in SP values that indicated a stock collapse for the two most female skewed sex ratios (Fi gure 3 3C). Again it was not easily discernable as to whether the remaining sex ratio scenarios at this fishing pressure had reached equilibrium at low levels or were slowly continuing to decline. Both total egg production (EP) and total fertilized egg pro duction (FEP) values mirrored the trends observed in FSSB. The greatest EP and FEP values resulted from the most female skewed scenarios and decreased with an increase in male skewing of the sex ratios (Figures 3 4 and 3 5). Once again, the proportion of t he change between the unfished and fished

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84 conditions was equivalent for all sex ratios, while the absolute value of the declines increased with increased female skewing in the sex ratio for both EP and FEP. Increasing values of F resulted in greater declin es in EP and FEP, and at the highest F value modeled ( F = 0.6) both EP and FEP values indicated a likely stock collapse for the most male skewed scenarios (Figures 3 4C and 3 5C). All sex ratios at F values of 0.2 and 0.4 reached stable asymptotic values, while the remaining sex ratios scenarios at an F of 0.6 appeared to either be continuing to decline or at very low equilibrium values (Figures 3 4 and 3 5). Again, in all cases the 1:1 sex ratio fell between the values of the male and female skewed scenar ios for all values of F There was only minor evidence of sperm limitation for the sex ratios that were modeled. If sperm limitation were occurring it would be detectable in two possible ways: 1) one sex ratio would have a greater FEP but lower EP than a s ex ratio with a greater female skew; or 2) the proportion of FEP/EP within a specific sex ratio scenario would be substantially less than the maximum fertilization rate that was modeled (0.8). There was a slightly decreased value of FEP/EP in comparison to the maximum fertilization rate of 0.8 for the 1:5 female skewed sex ratio prior to the onset of fishing (Figure 3 6). This deviation from the maximum rate was decreased after the onset of fishing for an F of 0.2 and was not apparent for higher values of F after the onset of fishing. There was also a temporary drop in the FEP/EP at the onset of fishing for the 1:5 scenario before the new equilibrium had been reached. The 1:3 sex ratio scenario also showed a small temporary drop in FEP/EP at the onset of fis hing prior to equilibrium being reestablished at the maximum value (Figure 3 6). Weighted spawning potential ratio (wSPR) and spawning potential ratio (SPR) values yielded a logical but unexpected result. Unlike the other output parameter values discussed above, both the proportion of change from the unfished to the fished condition and the absolute

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85 value of the change in wSPR and SPR values was the same regardless of the sex ratio (Figures 3 8 and 3 9). This occurred because these output parameters were th emselves proportions measuring the proportional change in some measure of fertilized eggs (FEP or fertilized eggs per recruit) from the unfished to fished condition. Hence their absolute changes reflected the changes in these proportions for different sex ratios. However, since there was no difference in the proportional change of FEP from the unfished to fished condition for different sex ratios, there was no difference in the absolute values of changes from the unfished to fished condition for wSPR or SPR The various forms of spawning potential ratios were compared to some general reference values, including 0.2 (Mace and Sissenwine 1993), 0.3 (Mace and Sissenwine 1993) and 0.4 (Clark 2002) to determine if recruitment overfishing was occurring. If the spa wning potential ratio was less than the reference value then the stock was considered to be recruitment overfished. The final wSPR values were 0.25, 0.09, and 0.03 for F values of 0.2, 0.4, and 0.6, respectively (Figure 3 7). These wSPR values indicated r ecruitment overfishing for F values of 0.4 and 0.6 for all three commonly used SPR reference values, while an F of 0.2 would produce wSPR values that would indicate recruitment overfishing for all but the least conservative reference value (0.2). The final SPR values were 0.33, 0.18, and 0.13 for fishing mortality rates of 0.2, 0.4, and 0.6, respectively (Figure 3 8). Again this indicated that F values of 0.4 and 0.6 would produce SPR values that were indicative of recruitment overfishing for all three SPR reference values. An F of 0.2 would produce SPR values indicating recruitment overfishing at only the most conservative reference point (0.4). Modeling Effects of Sex R atios R esulting from F ishing For all output parameters (MSSB, FSSB, SP, EP, FEP, wSPR, a nd SPR), the values prior to fishing were equivalent for all sex ratio scenarios due to the assumption of a 1:1 sex ratio prior

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86 to the onset of fishing (Figures 3 9 to 3 16). Following the initiation of fishing in year 51, the greatest values of MSSB occur red with 1:1, moderately male, or moderately female skewed sex ratios (Figure 3 9), while highly male or female skewed scenarios resulted in the lowest values of MSSB. An artifact of applying the sex ratios was apparent at the lowest fishing pressure ( F = 0.2), which resulted in a peak in MSSB immediately following the start of fishing (Year 51) for highly male skewed sex ratios (Figure 3 9A). This artifact was not evident at higher fishing pressures (Figure 3 9B and C). At the lowest level of fishing pres sure modeled, the more severely male skewed scenarios (3:1 and 5:1) showed a continuing trend of decreasing MSSB, however it appeared that the rate of decrease was slowing towards an equilibrium value. All other scenarios reached a stable value (Figure 3 9A). As fishing pressure increased, the potential for a stock collapse in male skewed sex ratios also increased. In the base case scenario for fishing pressure ( F = 0.4), a male skewed sex ratio of 5:1 leads to a complete collapse in MSSB, and a male skew of 3:1 results in a final value of MSSB that appeared to be following a continuing downward trend towards collapse (Figure 3 9B). The other sex ratio scenarios all reached relatively similar asymptotic values of MSSB. With the greatest fishing pressure mod eled ( F = 0.6), MSSB values for all male skewed sex ratios, except the 3:2 scenario, indicated a likely stock collapse (Figure 3 9C). The 3:2 sex ratio appeared to either be continuing a downward trend toward stock collapse or to have reached a very low st able level, while all other sex ratio scenarios had reached essentially the same low equilibrium value (Figure 3 9C). For all values of F the greatest FSSB after the onset of fishing occurred in the most female skewed scenarios and decreased as sex ratios become more male dominated (Figure 3 10). Similar to MSSB, there was an artifact of applying the sex ratios, which resulted in a peak in FSSB for highly female skewed sex ratios immediately following the start of fishing (Year 51)

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87 (Figure 3 10A). Again, t his artifact was not existent at higher fishing pressures (Figure 3 10B and C). At the lowest F value modeled ( F = 0.2), FSSB reached an equilibrium value for all sex ratios (Figure 3 10A). These equilibrium values covered a relatively wide range of FSSB v alues and decreased with increased male skewing. The base case sex ratio (1:1) fell inbetween the male and female skewed ratios. The two highly male skewed scenarios (3:1 and 5:1) resulted in a likely stock collapse at an F of 0.4. All other sex ratios re ached equilibrium values following the same order as for an F of 0.2, but reduced in value and over a smaller range of values (Figure 3 10B). At an F of 0.6, all male skewed sex ratios appeared to result in likely stock collapses, while all other sex ratio s reached low, but stable values of FSSB (Figure 3 11C). Sperm production (SP) followed the same pattern as observed in MSSB (Figure 3 11). As with MSSB, there was an artifact present in the male skewed sex ratios at the lowest fishing pressure that result ed in a peak in SP (Figure 3 11A), but again this artifact was lost as fishing pressure increased (Figure 3 11B and C). Even at the lowest value of F modeled ( F = 0.2), the most male skewed sex ratio (5:1) resulted in a considerable decrease in SP compare d to the 1:1 and moderately skewed (both male and female) sex ratios, and reached a similar equilibrium value to that of the most female skewed scenario (Figure 3 11A). All sex ratios reached relatively high equilibrium values with moderately male skewed a nd 1:1 sex ratios producing the highest values. With an F of 0.4 the most male skewed scenario resulted in a value indicative of a stock collapse, and the 3:1 sex ratio produced a continuing downward trend towards collapse (Figure 3 11B). SP was reduced es sentially to zero for the most male skewed sex ratios at an F of 0.6, while the moderately male skewed sex ratios appeared to either be continuing a downward trend or a very low equilibrium value (Figure 3 11C). The remaining sex ratios yielded low equilib rium levels of SP that were all approximately the same value.

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88 Total egg production (EP) mirrored the trends observed in FSSB with the highest values after the onset of fishing, for all fishing pressures, occurring in the most female skewed models and decre asing with an increasing male skew in the sex ratios (Figure 3 12). The artifact due to applying sex ratios was apparent at an F of 0.2 in the most female skewed sex ratios producing a peak in EP (Figure 3 12A). This artifact was not present at higher fi sh ing pressures (Figure 3 12B and C). All sex ratio scenarios for an F value of 0.2 resulted in equilibrium levels of EP being reached, with values decreasing with increased male skewing (Figure 3 12A). For an F of 0.4, male skewed sex ratios of 5:1 and 3:1 resulted in no egg production, while more moderately male skewed scenarios resulted in low equilibrium levels of EP (Figure 3 12B). Moderate male skewing resulted in EP values that appeared to be continuing a downward trend towards collapse and the most ma le skewed scenarios were indicative of a collapse at an F of 0.6. The remaining sex ratios reached equilibrium levels that decreased with a decreasing female skew, resulting in the 1:1 scenario having the lowest equilibrium level (Figure 3 12C). Total fer tilized egg production (FEP) followed the trends observed in EP. Again there was a peak in FEP at an F of 0.2 in the most female skewed sex ratios due to an artifact of applying the sex ratios (Figure 3 13A). This artifact was lost when F was increased (Fi gure 3 13B and C). The highest values of FEP for all values of F were observed in the models with the highest female skewing and decreased with an increase in male skewing of the sex ratios (Figure 3 13). With an F of 0.2, all sex ratios produced equilibri um values of FEP that decreased as male skewing increased (Figure 3 13A). The 3:1 and 5:1 male skewed sex ratios resulted in FEP values indicating a stock collapse at an F of 0.4, while all other sex ratios resulted in equilibrium levels that followed same pattern seen for an F of 0.2, but at decreased values (Figure 3 13B). At the highest fishing pressure modeled ( F = 0.6) the most male skewed scenario resulted in no

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89 FEP, while moderately male skewed scenarios appeared to be following a downward trend towa rds collapse. The female skewed and 1:1 sex ratios showed the same pattern of equilibrium values observed in the lower fishing pressures, but at decreased values (Figure 3 13C). For this set of models there was no substantial indication of sperm limitation for any of the sex ratios at any of the fishing mortality rates modeled (Figure 3 14). There was a minor, but detectable, drop in FEP/EP in the most female skewed sex ratio during the first year of fishing prior to an equilibrium being reestablished at th e maximum value of 0.8 (Figure 3 14). For both wSPR and SPR, the greatest values were obtained with the most female skewed sex ratios and decreased as the sex ratios became more male dominated (Figures 3 15 and 3 16). An artifact of applying the sex ratio s was present in the wSPR for an F of 0.2 for the most female skewed sex ratios, creating a peak in values in Year 51 when fishing started (Figure 3 15A). This artifact was not present in models with increased fishing pressure (Figure 3 15B and C). This ar tifact was also not present in SPR values for any of the model scenarios (Figure 3 16). For an F of 0.2, wSPR values for all male skewed sex ratios indicated that recruitment overfishing was likely occurring based on the lowest wSPR reference value of 0.2. The base case sex ratio (1:1) was also considered to be recruitment overfished based on wSPR reference values of 0.4 and 0.3. All female skewed scenarios would not be considered to be recruitment overfished with wSPR reference values of 0.2 and 0.3, and o nly the two most female skewed sex ratios would not be recruitment overfished using a wSPR reference value of 0.4 (Figure 3 15A). For the base case fishing pressure ( F = 0.4), all but the most female skewed sex ratio scenarios indicated that recruitment ov erfishing was occurring using the least conservative wSPR reference value (0.2), while at the other two wSPR reference values all sex ratios produced a situation indicative of recruitment overfishing (Figure 3 15B). The most

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90 male skewed scenarios completel y collapsed, and the moderately male skewed scenarios exhibited wSPR values indicative of substantial levels of recruitment overfishing at the least conservative wSPR reference value. All sex ratio scenarios resulted in a designation of being recruitment o verfished for all wSPR reference points at an F of 0.6, with all male skewed values indicating a likely stock collapse (Figure 3 15C). Trends in SPR were similar to those of wSPR, but final values were generally larger than those of wSPR, resulting in fewe r scenarios of recruitment overfishing (Figure 3 16). All female skewed sex ratios resulted in a designation of not being recruitment overfished for all three SPR reference values at an F of 0.2 (Figure 3 17A). The 1:1 scenario would not be considered to b e recruitment overfished at an F of 0.2 for SPR reference values of 0.2 and 0.3. Moderately male skewed sex ratios did not indicate recruitment overfishing for the least conservative SPR reference value (0.2), while the most male skewed scenarios produced SPR values indicative of recruitment overfishing for all reference points. In the base case scenario ( F = 0.4), no sex ratios produced SPR values greater than or equal to the 0.4 SPR reference value, and only the 1:5 female skewed sex ratio produced an SPR value greater than or equal to the 0.3 SPR reference value (Figure 3 16B). All female skewed sex ratios produced SPR values that indicated that they were likely not recruitment overfished using a SPR reference point of 0.2. The 1:1 sex ratio value fell sl ightly below the 0.2 SPR reference value and all male skewed scenarios were also considered to be recruitment overfished for all three SPR reference points. All sex ratio scenarios would result in designations of recruitment overfishing for the 0.3 and 0.4 SPR reference points for an F of 0.6, and only the 1:5 female skewed sex ratio would not be considered recruitment overfished using a SPR reference point of 0.2 (Figure 3 16C).

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91 Modeling Effects of Female Models based on fish >1 m FL showed that MSSB values for the 1:1 sex ratio were greater at all fishing pressures both prior to and after the onset of fishing compared to the corresponding model s with a 0.43:1 female skewed sex ratio (Figure 3 17A and B). After the onset of fishing, and with an increasing value of F the difference in MSSB between the 1:1 and the 0.43:1 scenarios was greatly reduced due to excess males being fished out in the 1:1 scenario. For the 0.43:1 scenario, the MSSB was reduced essentially to zero at an F of 0.6 (Figure 3 17B), and the corresponding value from the 1:1 sex ratio scenario appeared to be continuing to decrease towards collapse (Figure 3 17A). The MSSB values a t F values of 0.2 and 0.4 for both the 0.43:1 and 1:1 scenarios reached equilibrium levels, with values of MSSB at F = 0.4 considerably reduced in comparison to F = 0.2 values (Figure 3 17A and B). Initially FSSB was greater in the 0.43:1 sex ratio model compared to the 1:1 model due to the greater proportion of females in the largest size classes (Figure 3 18). This trend wa s maintained for an F of 0.2, but to a far lesser degree than in the unfished condition. In the base case scenario ( F = 0.4) FSSB va lues we re nearly identical after the onset of fishing for both sex ratio scenarios, and at an F of 0.6 the final FSSB values we re slightly larger in the 1 : 1 scenario (Figure 3 18A and B). As with MSSB, the FSSB value for an F of 0.6 for the 0.43:1 female s kewed scenario was reduced essentially to zero (Figure 3 18B), and the corresponding value for the 1:1 sex ratio scenario wa s reduced to a very low, but stable level (Figure 3 18A). For lower F values both sex ratio scenarios reach ed equilibrium levels, h owever the values for an F of 0.4 we re greatly reduced in comparison to an F of 0.2 (Figure 3 18A and B). Sperm production mirrored the trends seen in MSSB with the 1:1 sex ratio having greater SP values than the 0.43:1 sex ratio for all fishing pressure s, both prior to and after the onset of fishing (Figure 3 19A and B). The differences in the values between the two sex ratios were

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92 diminished after the onset of fishing. At F values of 0.2 and 0.4 both sex ratio scenarios reached equilibrium values, with the values for an F of 0.4 being considerably less than the values for an F of 0.2. The female skewed sex ratio for an F of 0.6 showed a continuing downward trend towards collapse, while the 1:1 scenario showed a low, but stable equilibrium level (Figure 3 19A and B). Both EP and FEP followed the trends observed for FSSB, with the greatest initial values occurring in the female skewed sex ratio scenarios (Figures 3 20 and 3 21). This trend was maintained throughout the model with an F of 0.2, but again to a lesser degree than in the unfished condition (Figures 3 20 and 3 21. In the fished condition the EP and FEP values were nearly identical at an F of 0.4, and with an F of 0.6 the 1:1 sex ratio scenario had slightly larger values for EP and FEP (Figures 3 2 0 and 3 21). Again an F of 0.6 resulted in values that would indicate a stock collapse for the female skewed sex ratio scenario for both EP and FEP (Figures 3 20B and 3 21B). As with the previous set of size based models, there was no indication of sperm l imitation as FEP/EP remained at the maximum value of 0.8 (Figure 3 22). For both wSPR and SPR, the final values were greater in the 1:1 sex ratio scenario than the 0.43:1 scenario, but only by a slight margin (Figures 3 23 and 3 24). Final wSPR values for both the 0.43:1 and 1:1 scenarios indicated recruitment overfishing for wSPR reference values of 0.3 and 0.4, and only at an F of 0.2 would wSPR values be above the wSPR reference value of 0.2 (Figure 3 23). None of the final SPR values were above the SPR reference of 0.4. The values for both sex ratios with an F of 0.2 were greater than the 0.2 and 0.3 SPR reference points, while the SPR values for F values of 0.4 and 0.6 fell below both of these SPR reference points (Figure 3 24).

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93 Sensitivity Analyses An increase in discard mortality ( D ) resulted in a decrease in all output parameters, while a decrease in D resulted in an increase in all output parameters for both types of models (Tables 3 4 and 3 5 ). The percent change (22 35%) was considerably greater th an 10% for all output parameters for both models with sex ratios applied at recruitment or based on size, except for SPR which showed percent changes that were only slightly greater than 10% (12 14%) (Tables 3 4 and 3 5). Changes in the maximum fertilizat ion rate, f max resulted in a percent change of approximately 26 28% for FEP in the models with sex ratios applied at recruitment (Table 3 4) and a percent change of approximately 17 27% in FEP for the models with sex ratios applied based on size/age (Tabl e 3 5). The percent changes were positive for an increase in f max and negative for a decrease in f max All the remaining output parameters were changed by less than 10% for both types of models, and there was no clear pattern in whether the change was posi tive or negative based on whether f max was increased or decreased (Tables 3 4and 3 5). SPR values were completely unchanged when f max was changed. The alternate value of which defines the steepness of the fertility curve, produced no percent changes greater than 10% in any of the output parameters for either type of model (Tables 3 4 and 3 5). As with f max a change in resulted in no change in SPR (Tables 3 4 and 3 5) Increasing the virgin recruitment ( R o ) resulted in a large positive change for most output parameters, with a decrease in R o having the opposite effect (Tables 3 4 and 3 5). In contrast to most other parameters, wSPR showed percent changes well below 10% for both types of models and SPR showed no changes (Tables 3 4 and 3 5). Changes in the previous input parameters resulted in changes in the output parameters that were similar in magnitude for both positive and negative changes of the input parameters.

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94 However, changes in recK input resulted in large, and asymmetrical, differences in the magnitude of change between equivalent positive and negative changes. Decreasing recK resulted in 87 89% negative changes in all output parameters except SPR, which was unchanged, for both types of models ( Tables 3 4 and 3 5). Increasing the value of recK resulted in positive percent changes in all output parameters, except SPR that was again unchanged, but these changes (30 41%) were much less than the percent changes (8 6 90%) for the equivalent decrease in recK (Tables 3 4 and 3 5). Discussion Sex ratios skewed toward one sex or the other can have substantial effects on the productivity of a stock regardless of what size/age that skewing begins to occur at. In general, f emale skewed scenarios tended to result in higher productivity and greater resilience to exploitation, while male skewed scenarios often had decreased productivity and resilience to exploitation, with the 1:1 sex ratio scenario generally falling between th e two extremes. High degrees of male skewing often resulted in output parameters indicating a likely stock collapse or output parameters that were following a continuing downward trend towards collapse. Increasing fishing pressure resulted in some of the m oderately male skewed scenarios indicating a likely stock collapse. Often moderately male skewed scenarios, and at higher fishing pressures the 1:1 and moderately female skewed scenarios, yielded stable but very low levels for the output parameters. Such l ow levels could easily be driven to collapse due to some type of perturbation(s) in the system. For all the sex ratio models in the present study, the driving component of the productivity appeared to be associated with female fish because there was littl e or no indication of sperm limitation. This was not completely unexpected as instances where sperm limitation does occur are generally associated with protogynous species that can show considerably larger female

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95 skewing (Heppell et al. 2006). The one inst ance of minor sperm limitation occurred for the most female skewed sex ratio modeled (1:5) for a scenario in which the sex ratio was applied at recruitment. However, it is unlikely that the overall sex ratio for greater amberjack would approach this value (Chapter 2), much less the degree of female skewing that would be required to cause a substantial level of sperm limitation. Other than this one instance of sperm limitation, all plots of FEP/EP showed that all sex ratios yielded a value of 0.8 for this ra tio, which is the maximum fertilization rate that could be achieved based on model parameterization. Lower values could be achieved, as evidenced by the one instance of minor sperm limitation; however values of FEP/EP did not decline in most scenarios beca use the proportion of males in the spawning stock did not decrease by a large enough degree to drop off the asymptote predicted by the fertility function, which is an exponential function. In modeling sex ratios applied at recruitment, differences in outpu t parameters between different sex ratios were apparent both before and after the onset of fishing. The proportion of the change in a particular output parameter from the unfished to the fished condition was the same for all sex ratios, but the absolute va lue of these changes were different for each sex ratio. This would tend to indicate that all of the different sex ratios would produce the same outcomes, in terms of being overfished or not, under the same fishing pressure. However, if the sex ratio is dif ferent than that which is assumed, then the presumed fishing pressure exerted on females (the sex that drives productivity in this stock) in the stock may actually be higher or lower because of differences in the abundance of females at different sex ratio s present prior to fishing. For example, if the sex ratio is assumed to be 1:1, the value assumed in the most recent stock assessment for Gulf of Mexico greater amberjack (NMFS 2006), and fished under this assumption with a quota in place based on the prod uctivity of this sex ratio, but in fact the sex

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96 ratio is male skewed, then the quota based on the 1:1 sex ratio would increase the actual fishing mortality experienced by females. Such a situation could lead to severe overfishing of the stock. Some of the commonly used output parameters for models with sex ratios applied at recruitment can be misleading. MSSB and SP were highest for the most male skewed scenarios, giving the impression that these sex ratios may be the most productive; however, the values of FSSB, EP, and FEP were the highest for the most female skewed scenarios and lowest for the most male skewed scenarios. As was stated previously, the female related output parameters were likely the best indicators of the productivity of a particular sex r atio scenario, as there was little or no indication of sperm limitation for all model scenarios (i.e., the productivity was not limited by male abundance). Both wSPR and SPR showed no differences between any of the sex ratios. This resulted from the fact t hat these output parameters are proportions based on some measure (FEP or fertilized eggs per recruit) of the unfished and fished number of fertilized eggs, which as stated previously were the same for all sex ratios. With no other output parameters for re ference, one could potentially think that there were no differences in the number of fertilized eggs produced between the different sex ratios leading to inappropriate management of the stock. The reference values used to determine if wSPR and SPR values a re indicative of recruitment overfishing may be based on life history parameters of a particular species or stock, but there is no set criteria for the selection of the reference value used and few empirical studies examining how to choose a reference valu e (Mace and Sissenwine 1993). This can lead to a somewhat arbitrary assignment of reference values, and thus spawning potential ratios may be misleading. In the analysis for this study, a range of commonly used reference values (0.2, 0.3, and 0.4) was used which demonstrated how uncertainty in this value could influence whether a particular scenario would result in recruitment overfishing. Greater amberjack are a relatively

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97 fast growing and short lived species with high fecundity. Such a life history patte rn can result in a higher resilience to recruitment overfishing, in which case a lower reference value such as 0.2 could be used. However, without specific research focused on determining an appropriate reference value the results should be treated with ca ution and it is advisable to error on the conservative side in stock management. In models in which sex ratios were applied based on size, differences were not apparent until fishing had begun due to the assumption of a 1:1 sex ratio prior to fishing. Unli ke the models with sex ratios applied at recruitment, the most male skewed sex ratios did not produce the highest MSSB or SP, but, in fact, produced the lowest values for these parameters. This was because in these scenarios a highly male skewed sex ratio arises from a large reduction in FSSB, which results in an overall decreased population and hence a decrease in the number of males. The most female skewed sex ratios also produced relatively low values of MSSB and SP due to the necessary decrease in the n umber of males to produce the female skewing. This resulted in the 1:1 and moderately skewed sex ratios having the highest values for these two output parameters. Because the most male skewed sex ratios do not produce the highest values of MSSB and SP, but rather produce the lowest value, they tend not to be as misleading in assessing the productivity of a stock, as was the case for models with sex ratios applied at recruitment. However, there was still no evidence of sperm limitation, which indicated that FSSB, EP, and FEP were the output parameters that would limit productivity. These parameters were the highest in the most female skewed sex ratios and lowest in the most male skewed sex ratios. Moderately skewed and the 1:1 sex ratios produced FSSB, EP, an d FEP values in between the extremes, whereas these sex ratios produced the highest values of MSSB and SP, resulting in these latter parameters still being somewhat misleading in regards to stock productivity. Female skewed sex

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98 ratios tended to be more res ilient to fishing due to their higher productivity, but this resilience was decreased with increasing fishing pressure. Spawning potential ratios were more straightforward to interpret for these models as the initial values of FEP and fertilized eggs per r ecruit were equivalent for all of the sex ratios (the proportions between unfished and fished conditions were different for each sex ratio). In relation to three commonly used reference points (0.2, 0.3, and 0.4) for assessment of recruitment overfishing, the likelihood of overfishing increased with an increasing male skew in sex ratio and with increasing fishing pressure. A number of sex ratio scenarios over the F values modeled yielded wSPR and SPR values indicative of recruitment overfishing, and for the base case scenario ( F = 0.4) only female skewed sex ratio scenarios resulted in a designation of not recruitment overfished regardless of the reference value used. The current F for the Gulf of Mexico greater amberjack stock is likely 0.4 or higher, and c urrently this stock is considered to be overfished and undergoing overfishing (NMFS 2006). Therefore, even though this study used different designation criteria for overfished status it is not surprising that most scenarios yielded designations of being ov erfished. The model investigating female skewing in fish over a meter in length demonstrated that initially female skewing of these large individuals resulted in higher productivity due to the greater values of FSSB, EP, and FEP. This advantage was quickl y diminished with the onset of fishing, which resulted in the removal of the excess large females in the female skewed scenario. At all but the lowest fishing pressure, the 1:1 sex ratio attained a similar or greater level of productivity after the onset o f fishing in comparison to the female skewed scenario. Overall, female biomass and egg production were likely the driving factors of productivity for the Gulf of Mexico greater amberjack stock. Model scenarios in which the sex ratio was

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99 female skewed tende d to have added resilience to fishing pressure, however, this extra resilience was greatly reduced as fishing pressure increased. The added reproductive output observed in the scenario with female skewing in the largest size classes was quickly diminished after the onset of fishing. One possibility that could help to maintain the higher productivity resulting from female skewing, particularly in the largest size classes, would be to impose a slot limit in the fishery, in which fish > 1 m FL or some slightly larger size would have to be released while also maintaining the minimum FL size limit. The potential success of such a measure would in part depend on the survival of fish that had to be released after capture due to the slot limit. The survival of relea sed greater amberjack is currently being studied (D. Murie and D. Parkyn, University of Florida, personal communication). Another potential problem with implementing a slot limit would be determining if it should be applied to both recreational and commerc ial sectors of the fishery, particularly since under current regulations a large percentage of commercially harvested fish are over a meter in length (commercial minimum size limit = 36 in or 914.4 mm FL). Therefore, for a slot limit to be effective in the commercial fishery the minimum size limit would also have to be reduced. The sensitivity analysis of several input parameters demonstrated that with these age, size, and sex based models some inputs have substantially more weight on the output parameters than others. This was the case regardless of how the sex ratios were applied. SPR values were unchanged in the sensitivity analysis of all input parameters, other than discard mortality. This occurred because SPR values were based on an average lifetime p er recruit production of some reproductive output (fertilized eggs in this case), which in its simplest form can be reduced to equilibrium values for unfished and fished conditions. These equilibrium values differ on the basis of mortality rates alone in t he scenarios modeled. The only other

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100 possibilities that would result in changes in the value of SPR would be if the mortality schedules or fecundity schedules of the fish were altered from the unfished to the fished condition. Discard mortality ( D ) had a substantial effect on all output parameters. It has also been important in many of the assessment models used for this stock (NMFS 2006), making the determination of its actual value of particular importance. Currently, research is being conducted to exami ne discard mortality and what factors may influence it (D. Murie and D. Parkyn, University of Florida, personal communication). With such a heavy weight on model outputs, it would be advisable to investigate a range of potential values and potentially erro r on the side of caution until better estimates of this value have actually been determined. Currently, stock assessment models for the Gulf stock that incorporate discard mortality also conduct sensitivity analyses on this parameter (NMFS 2006). Both of t he fertility parameters, f max and had a very minor impact on the output parameters. The fact that changes in these parameters had little effect on the output parameters supports the notion that male abundance (MSSB) and productivity (SP) were not likely to be limiting factors for the ov erall productivity of this stock. As mentioned previously, there is little empirical data available on male reproductive parameters, and much of what is known has been derived from captive settings (Trippel 2003). In many cases, models investigating male reproductive potential rely on theoretical values or values derived from similar species (Alonzo and Mangel 2004, 2005; Heppell et al. 2006; Molloy et al. 2007). The values of f max that were modeled were based on estimates derived from captive individuals that could possible exceed The mating structure of a species may also have an impact on how male abundance influences population dynamics (Trippel 2003; Alonz o and Mangel 2004, 2005), but there is currently no

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101 data available regarding the mating structure of greater amberjack in the wild. These factors may have influenced the value of the male associated reproductive output parameters (MSSB, SP, and FEP), howev er, there was such minor evidence of sperm limitation and the fertility parameters had such little influence in the sensitivity analysis that it is likely a ny differences would be minor. Trippel (2003) outlines a number of possible research areas and metho ds that could be used to further investigate the reproductive output of males if there were greater concern for sperm limitat ion in this or other species. Changes in recruitment parameters can greatly influence the values of the output parameters for these models. This was to be expected as it is generally the case that any variation on a statistical catch at age model (forward moving age based model) is driven by several leading parameters, which generally include one or more recruitment parameters (Walter s and Martel 2004). Changes in the value of virgin recruitment ( R 0 ) resulted in substantial percent changes for nearly all output parameters. These percent changes were not as large as those for discard mortality; however, the percent change between the or iginal and alternate values of discard was 100% in comparison to a 14% change in virgin recruitment values. The recruitment compensation ratio ( recK ) was by far the most important of the input parameters investigated in the sensitivity analysis. The percen t changes for equivalent increases and decreases in recK were not similar in magnitude as was the case for the other input parameters. It appeared that a decrease in recK had a greater effect on productivity than an equivalent increase in recK It was more probable that the recK used in this model would be an underestimate of the actual value rather than an over estimate, as most recK values for species with similar life histories were equal to or greater than the selected value and there were only a few th at were lower than the selected value (Meyers et al. 1999). However, this study sought to determine if skewing of sex

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102 ratios could influence the population dynamics of a gonochoristic fish species in a similar manner to that seen in sex changing species an d any direct application of this type of model to a stock assessment would benefit from better stock recruitment parameter estimates based on fertilized egg production. Since male abundance and productivity appeared to have little influence on the overall productivity of this stock, this model could be modified to incorporate a recruitment function based on some other measure of female reproductive potential, such as female spawning stock biomass, rather than fertilized egg production. This would allow for the use of the hockey stick recruitment function employed in the most recent stock assessment for Gulf of Mexico greater amberjack. A modification of this model to incorporate a different recruitment function would then place the weight of recK on the para meters of the new function, and some accurate measure of virgin recruitment would still be required. There are some other factors to consider that could improve the model used in this study. For all of the models, the sex ratios and fishing mortality rates were directly applied, but a gradually changing sex ratio and F value may more accurately simulate changes within the Gulf of Mexico stock. For the models in which sex ratio was applied at a specific size/age, the sex ratios were applied in a knife edge m anner rather than a stepped manner, which would better incorporate variability in size at age. Using a stepped application of sex ratios would likely produce the same general patterns but shifted by a certain degree due to a portion of younger fish experie ncing the shifts in sex ratio. It was also assumed that the number of spawnings per year was equivalent for all mature females. This may not be the case, and further research in this area is still needed. This model could, however, be adapted to simulate t he effects of varying spawning frequency based on fish size/age.

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103 It is clear that skewing within sex ratios of gonochoristic fish species, whether arising naturally or from sex selective fisheries, can greatly alter the productivity of a stock. These resu lts were similar to those found for both protandrous (Molloy et al. 2007) and protogynous (Huntsman and Schaaf 1994; Alonzo and Mangel 2004, 2005; Heppell et al. 2006) fish species. In protogynous species, the reduction in productivity generally results fr om sperm limitation. In this study, there was no evidence of sperm limitation in any of the models. This may arise from several factors. As previously stated, the female skewed sex ratios that were modeled in this study were considerably less skewed than t hose of stocks that have demonstrated potential sperm limitation. Another factor that may eliminate the potential for sperm limitation in the greater amberjack stock is the fact that males generally mature earlier than females in thi s species (Tables 1 1 a nd 3 3). It is clear from this study that an incorrect assumption of the sex ratio in a gonochoristic species, such as greater amberjack, could lead to mismanagement of the stock. Assuming that a sex ratio is more male skewed than it actually is would like ly result in underutilization of the stock, while assuming that a sex ratio is more female skewed than it actually is would likely result in overexploitation of the stock. Currently the Gulf stock is assumed to have a 1:1 sex ratio, and estimates obtained from non lethal sexing (Chapter 2) appear to support this assumption. However, sex ratio estimates from other data sources, such as port sampling (Chapter 2), point towards an overall female skewing in the sex ratio. If this is actually the case, the Gulf stock may not be as exploited as current stock assessment models predict. However, if the greater number of females seen in port samples is not due to a female skew in the sex ratio, but from sex selectivity of the fisheries (i.e., females are being differ entially harvested due to greater growth rates or spatial and/or temporal patterns in sex ratios), then the overall sex ratio

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104 could be being driven towards a male skew, which would result in an underestimation of the current exploitation by assuming a 1:1 sex ratio. A range of realistic estimates of sex ratios for the Gulf of Mexico stock of greater amberjack should therefore be used in the stock assessment, rather than continuing to simply assume a sex ratio of 1:1. More detailed data on sex ratios may als o help to identify potential spatial and temporal trends in sex ratios related to possible sex specific schooling and/or migration patterns, which in addition to size limits may result in sex specific exploitation of one sex or the other. Such data could p otentially be used to impose geographic or temporal regulations, such as designated closures, either in space or time, aimed at protecting aggregations of female fish, particularly th ose in the largest size class

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105 Table 3 1. Input parameters for models. Va lues in parentheses indicate values used in sensitivity analysis. Parameter Value Source von Bertalanffy growth parameters L (mm) Male 1196.6 Murie and Parkyn 2008 Female 1279.6 Murie and Parkyn 2008 Combined 1240.5 Murie and Parkyn 2008 K Male 0.29 Murie and Parkyn 2008 Female 0.26 Murie and Parkyn 2008 Combined 0.28 Murie and Parkyn 2008 t 0 Male 0.92 Murie and Parkyn 2008 Female 1.12 Murie and Parkyn 2008 Combined 1.01 Murie and Parkyn 2008 Weight length parameters a 6.7x10 8 Murie and Parkyn 2008 b 2.765 Murie and Parkyn 2008 Mortality M 0.25 NMFS 2006 F 0.2, 0.4, 0.6 NMFS 2006 D 0.2 (0.0, 0.4) NMFS 2006 Proportion Legal M SL (commercial) 762 Hood 2006 M SL (recreational) 914.4 Hood 2006 SL*0.1 Coggins et al. 2007; Pine et al. 2008; Tetzlaff et al. 2011 Fecundity a f 655746 Harris et al. 2007 b f 387.897 Harris et al. 2007 N 14 Harris et al. 2007 Fertility f max 0.8 (0.6, 1.0) Jerez et al. 2006 20 (80) Heppell et al. 20 06 Recruitment recK 10 (5, 15) Meyers et al. 1999, Goodwin et al. 2006 R 0 3.5x10 5 (3.0x10 5 4.0x10 5 ) Diaz et al. 2005

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106 Table 3 2. Gear selectivites for Gulf of Mexico greater amberjack. CMHL = commerical handline, C MLL = commercial longline, HB = headboa t, CB+PB = combined recreational charter and private fisheries. Values from Diaz et al. ( 2005 ) Gear Age 1 2 3 4 5 6 7 8 9 10+ CMHL 0.0 0.0 0.2 0.8 1.0 1.0 1.0 1.0 1.0 1.0 CMLL 0.0 0.0 0.0 0.5 0.9 1.0 1.0 1.0 1.0 1.0 HB 0.0 1.0 0.9 0.4 0.0 0.0 0.0 0.0 0.0 0.0 CB+PB 0.0 0.9 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Table 3 3. Proportion of mature male and female Gulf of Mexico greater amberjack by age. Female values from Murie and Parkyn ( 2008 ) and male values from D. Murie and D. Parkyn (University of Florida, unpublished data) Sex Age 1 2 3 4 5 6 7 8 9 10+ Male 0.103 0.103 0.597 0.804 0.806 1.000 1.000 1.000 1.000 1.000 Female 0.029 0.067 0.225 0.844 0.857 0.900 1.000 1.000 1.000 1.000

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107 Table 3 4. S ensitivit y analysis for Gulf of Mexico greate r amberjack models with sex ratios applied at recruitment. Bold denotes a relevant percent change ( 10% from the base case scenario at original value) Input parameter Original Value Alternate Value 1 Alternate Va lue 2 Output parameter % Change for alternate value 1 % Change for alternate value 2 D 0.2 0.0 0.4 MSSB 34.89 21.94 FSSB 22.12 31.75 EP 31.04 27.45 SP 30.05 27.58 FEP 32.15 26.69 wSPR 24.36 29.75 SPR 13.60 12.01 f max 0.8 0.6 1.0 MSSB 2.72 3.60 FSSB 1.18 0.14 EP 3.04 3.81 SP 2.00 4.97 FEP 26.43 27.43 wSPR 3.75 4.04 SPR 0.00 0.00 20 80 MSSB 2.82 FSSB 0.76 EP 2.11 SP 0.54 FEP 1.22 wSPR 3.48 SPR 0.00 R 0 350000 300000 400000 MSSB 12.61 21.41 FSSB 13.93 13.25 EP 14.07 12.11 SP 16.74 12.90 FEP 13.14 12.63 wSPR 5.52 1.93 SPR 0.00 0.00 recK 10 5 15 MSSB 86.84 40.28 FSSB 88.73 34.13 EP 88.52 38.06 SP 88.58 31.11 FEP 89.12 37.26 wSPR 88.98 32.88 SPR 0.00 0.00

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108 Table 3 5. S ensitivity analysis for Gulf of Mexico greater amberjack m odels with sex ratios applied based on size. Bold deno tes a relevant percent change ( 10% from the base case scenario at original value) Input parameter Original value Alternate value 1 Alternate value 2 Output parameter % Change for alternative value 1 % Change for alternative value 2 D 0.2 0 0.4 MSSB 23.88 30.15 FSSB 33.50 32.75 EP 24.56 26.42 SP 25.79 24.37 FEP 26.58 30.61 wSPR 27.92 29.40 SPR 14.08 12.37 f max 0.8 0.6 1.0 MSSB 4.06 6.65 FSSB 4.11 0.70 EP 1.13 0.39 SP 3.41 1.74 F EP 26.78 16.96 wSPR 4.59 1.24 SPR 0.00 0.00 20 80 MSSB 2.06 FSSB 0.61 EP 5.40 SP 2.19 FEP 0.98 wSPR 0.43 SPR 0.00 R 0 350000 300000 400000 MSSB 16.84 11.86 FSSB 15.92 12.59 EP 15.90 9.55 SP 12.64 13.10 FEP 17.60 11.04 wSPR 0.40 3.88 SPR 0.00 0.00 recK 10 5 15 MSSB 87.80 30.31 FSSB 87.34 33.68 EP 87.17 33.94 SP 86.72 38.19 FEP 88.20 30.49 wSPR 88.00 40. 75 SPR 0.00 0.00

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109 Figure 3 1. Male spawning stock biomass (MSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and t he base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) 0 51 100 Years B) F = 0.4 C) F = 0.6 A) F = 0.2 MSSB (millions (kg)

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110 Figure 3 2. Female spawning stock biomass (FSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fisihng was initiated jn year 51. Sex Ratio (m:f) 0 51 100 Years FSSB (million s (kg) B) F = 0.4 C) F = 0.6 A) F = 0.2

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111 Figure 3 3. Total sperm production (SP) of Gulf of Mexico grea ter amberjack for models with a range of sex ratios applied at recruitment F valu es of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) Sperm 0 51 100 Years B) F = 0.4 C) F = 0.6 A) F = 0.2

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112 Figure 3 4. Total egg production (EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) 0 51 100 Years Eggs B) F = 0.4 C) F = 0.6 A) F = 0.2

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113 Figure 3 5. Total fertilized egg production (FEP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) Fertilized Eggs 0 51 100 Years B) F = 0.4 C) F = 0.6 A) F = 0.2

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114 Figure 3 6. Ratio of fertilized egg production to egg production (FEP/EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Values less than the maximum fertilization rate modeled (0.8 ) indicated potential sperm limitation. Fishing was initiated in year 51. All sex ratio are graphed, but most are stacked due to equivalent values of FEP/EP. FEP/EP Sex Ratio (m:f) 0 51 100 Years B) F = 0.4 C) F = 0.6 A) F = 0.2

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115 Figure 3 7. Weighted spawning potential ratio (wSPR) of G ulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Horizontal lines represent wSPR referen ce values. Sex Ratio (m:f) wSPR 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2 0.4 0.3 0.2 Reference Value

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116 Figure 3 8. Spawning potential ratio (SPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at recruitment over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the bas e case F was 0.4. Fishing was initiated in year 51. Horizontal lines represent SPR reference values. Sex Ratio (m:f) SPR 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2 0.4 0.3 0.2 Reference Value

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117 Figure 3 9. Male spawning stock biomass (MSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. MSSB (millions (kg) 0 51 100 Years Sex Ratio (m:f) B) F = 0.4 C) F = 0. 6 A) F = 0. 2

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118 Figure 3 10. Female spawning stock biomass (FSSB) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) FSSB (millions (kg) 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2

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119 Figure 3 11. Total sperm production (SP) of Gulf of Mexico greater amberjack for model s with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sexratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) Sperm 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2

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120 Figure 3 12. Total egg production (EP) of Gulf of Mexico greater amb erjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sexratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) Eggs 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2

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121 Figure 3 13. Total fertilized egg production (FEP) o f Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Sex Ratio (m:f) Fertilized Eggs 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2

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122 Figure 3 14. Ratio of ferti lized egg production to egg production (FEP/EP) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over a F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Values less than the maxi mum fertilization rate modeled (0.8) indicated the potential for sperm limitation. Fishing was initiated in year 51. All sex ratios are graphed, but are stacked due to equivalent values of FEP/EP. FEP/EP 0 51 100 Years Sex Ratio (m:f) B) F = 0.4 C) F = 0. 6 A) F = 0.2

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123 Figure 3 15. Weighted spawn ing potential ratio (wSPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Horizontal lin es represent wSPR reference values. Sex Ratio (m:f) wSPR 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2 0.4 0.3 0.2 Reference Value

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124 Figure 3 16. Spawning potential ratio (SPR) of Gulf of Mexico greater amberjack for models with a range of sex ratios applied at age 3 over F values of 0.2 to 0.6. The base case sex ratio was 1:1 and the base case F was 0.4. Fishing was initiated in year 51. Horizontal lines represent SPR reference values. Sex Ratio (m:f) SPR 0 51 100 Years B) F = 0.4 C) F = 0. 6 A) F = 0.2 0.4 0.3 0.2 Reference Value

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125 Figure 3 17. Male spawning stock biomass (MSSB) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio; B) and a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Fishing was initiated in year 51. 0 51 100 Years 0 51 100 Years MSSB (millions kg) F B) 0.43:1 A) 1:1

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126 Figure 3 18. Female spawning stock biomass (FSSB) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio; and B) a 3:7 female skewed sex ratio for fish > 1 m fork length. Fishing was initiated in year 51. 0 51 100 Years 0 51 100 Years FSSB (millions kg) F B) 0.43:1 A) 1:1

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127 Figure 3 19. Total sperm production (SP) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio; and B) a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Fishing was initiated in year 51. 0 51 100 Years 0 51 100 Years Sperm F B) 0.43:1 A) 1:1

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128 Figure 3 20. Total egg production (EP) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio ; and B) a 0.43:1 female skewed sex ratio for fish > 1 m for k length. Fishing wa s initiated in year 51. Eggs F 0 51 100 Years 0 51 100 Years B) 0.43:1 A) 1:1

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129 Figure 3 21. Total fertilized egg production (FEP) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio; and B) a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Fishing was initiated in year 51. 0 51 100 Years 0 51 100 Years Fertilized Eggs F B) 0.43:1 A) 1:1

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130 Figure 3 22. Ratio of fertilized egg production to egg production for Gulf of Mexico greater amberjack across a range of F values (0.4 = b ase case) for A) the base case 1:1 sex ratio; and B) a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Values less than the maximum fertilization rate modeled (0.8) indicated the potential for sperm limitati on. Fishing was initiated in year 51. All F values are graphed but are stacked due to equivalent values of FEP/EP. 0 51 100 Years 0 51 100 Years FEP/EP F B) 0.43:1 A) 1:1

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131 Figure 3 23. Weighted spawning potential ratio (wSPR) for Gulf of Mexico greater amberjack acro ss a range of F values (0.4 = base case) for A) the base case 1:1 s ex ratio; and B) a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Fishing was initiated in year 51. Horizontal lines represent wSPR reference values. wSPR 0 51 100 Years 0 51 100 Years F B) 0.43:1 A) 1:1 0.4 0.3 0.2 Reference Va lue

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132 Figure 3 24. Spawning potential ratio (SPR) for Gulf of Mexico greater amberjack across a range of F values (0.4 = base case) for A) the base case 1:1 sex ratio; and B) a 0.43:1 female skewed sex ratio for fish > 1 m fork length. Fish ing was initiated in year 51. Horizontal lines represent SPR reference values. 0 51 100 Years 0 51 100 Years SPR F B) 0.43:1 A) 1:1 0.4 0.3 0.2 Reference Value

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133 CHAPTER 4 CONCLUSION Information related to reproduction and sex specific parameters in the Gulf of Mexico greater amberjack stock, which is considered to be overfished and un dergoing overfishing, is still in need of further study. The development of a non lethal means of sex determination for this species will allow for a considerable increase in our knowledge of sex specific mortality and migration patterns, as well as determ ining more accurate sex ratios. Such information will allow for more well informed stock assessments and better management of this stock. The use of external urogenital features has been used to non lethally sex fish for a number of years, and in general t he results of studies applying this method have yielded high accuracies. However, advances in technology and the relatively simple nature of this method have likely resulted in it falling to the wayside in many cases, with a more technologically advanced m ethod being used instead. In some instances, a simple yet accurate method may actually be desirable, as is the case with non lethally sexing a relatively large species that is to be immediately released while at sea. The use of external urogenital features requires no anesthesia, minimal costs and training, and is relatively rapid to perform, thus making it a good choice for application in attempting to sex such a species (greater amberjack in this case) at sea. The results of this study have shown that the use of external urogenital features is indeed an accurate means by which the sex of greater amberjack can be determined non lethally as accuracies remained high regardless of the sex or size of an individual. Although reproductively active fish are by far the easiest to sex using this method, non reproductively active individuals can also be sexed with relative ease. However, the utility of this method is likely diminished at a lower size threshold based on the small size of the urogenital pores (i.e., no amberjack <500 mm FL were sexed in this study).

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134 Urogenital catheterization is another commonly used method for non lethally sexing fish. Again, this is a relatively simple method requiring no anesthesia, minimal costs and training, and it is relatively rap id. This method has previously been used to determine the maturation state of greater amberjack in an aquaculture setting, and in this study it proved to be effective in verifying sexes determined by the use of external urogenital features and assessing th e relative maturity of female fish. The ability to non lethally sex greater amberjack would add a great deal to our knowledge of the species if applied in tag and release studies, on board observer programs, and scientific surveys. The combination of the t wo previously mentioned methods could allow for determination of sex specific mortality rates, growth rates, and migration patterns, as well as better estimates of sex ratios, both overall and regionally. In addition, these methods could be used in an atte mpt to locate areas of spawning aggregations. The information relating to reproduction and sex specific parameters can be used to better understand the population dynamics of the Gulf of Mexico greater amberjack stock and lead to better management. This st udy modeled the potential impacts of sex ratios on the population dynamics of this stock. The sex ratios modeled were based on data from both lethal (port sampling, age and growth studies, etc.) and non lethal (tag and release study) studies. The results o f this study indicated that sex ratios can play a significant role in the estimation of productivity of greater amberjack. Even moderate male skewing of the sex ratio of the individuals remaining in the Gulf stock can lead to a large decrease in productivi ty at current fishing mortality rates, while female skewing could impart some resilience to fishing. The differences in productivity between male and female skewed and un skewed populations were decreased with increasing fishing pressure. The female skewi ng that was observed in the largest size classes of this species

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135 also imparted some resilience to fishing pressure, but this resilience was quickly diminished upon the onset of fishing as the largest individuals were fished out. Sexually dimorphic growth c ould lead to sex specific exploitation which may lead to an alteration of the overall sex ratio. The current stock assessment for Gulf of Mexico greater amberjack assumes a 1:1 sex ratio. However, there was some evidence that the overall sex ratio of land ings was moderately female skewed, which could either indicate that the overall sex ratio for the Gulf of Mexico greater amberjack stock was female skewed or that the female skewing in the landings could be creating an overall sex ratio that was male skewe d. Site specific sex ratios can also be highly skewed, but no clear patterns have emerged. Further research may reveal sex specific migration patterns and regional skewing in sex ratios that could lead to further sex specific exploitation. Knowledge that s kewing of sex ratios can greatly affect the productivity of this species should be taken into account in its stock assessment. An erroneous sex ratio assumption (i.e., 1:1) could result in incorrect conclusions being made about its current stock status. A remaining population is more female skewed than is assumed may actually not be as exploited as would be concluded, while a stock with a remaining population that is more male skewed than is assumed is likely to be more exploited than would be c oncluded. With this in mind, future stock assessments should at look at different sex ratio scenarios to provide upper and lower bounds of exploitation and current stock status.

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136 REFERENCES Alam, M.A. and M. Nakamura. 2008. Determination of sex and gonada l maturity in the honeycomb grouper, Epinephelus merra through biopsy. Aquaculture International 16: 27 32. Alonzo, S. H. and M. Mangel. 2004. The effects of size selective fisheries on the stock dynamics of and sperm limitation in sex changing fish. Fish eries Bulletin 102: 1 13. Alonzo, S. H. and M. Mangel. 2005. Sex change rules, stock dynamics, and the performance of spawning per recruit measures in protogynous stocks. Fisheries Bulletin 103: 229 245. Alonzo, S. H., T. Ish, M. Key, A. D. MacCall, and M. Mangel. 2008. The importance of incorporating protogynous sex change into stock assessments. Bulletin of Marine Science 83(1): 163 179. Alvarez Lajonchre, L., D. Guerrero Tortolero, and J. C. Perez Urbiola. 2001. Validation of an ovarian biopsy method in a sea bass, Centropomus medius Gnther. Aquaculture Research 32: 379 384. Armsworth, P. R. 2001. Effects of fishing on a protogynous hermaphrodite. Canadian Journal of Fisheries and Aquatic Sciences 58: 568 578. Asturiano, J., L. A. Sorbera, J. Ramos, D. E. Kime, M. Carrillo, and S. Zanuy. 2002. Group synchronous ovarian development, ovulation and spermiation in the European sea bass ( Dicentrarchus labrax L.) could be regulated by shifts in gonadal steroidogenesus. Scientia Marina 66(3): 273 282. Bailey, R and B. Cole. 1999. Spawning the tinfoil barb, Barbodes schwanenfeldi in Hawaii. Center for Tropical and Subtropical Aquaculture, University of Hawaii, Publication Number 136, Honolulu, Hawaii. Barrowman, N. J. and R. A. Myers. 2000. Still more spawner r ecruitment curves: the hockey stick and its generalizations. Canadian Journal of Fisheries and Aquatic Sciences 57: 665 676. Beasley, M. L. 1993. Age and growth of greater amberjack, Seriola dumerili from the northern Gulf of Mexico. M.S. thesis. Louisian a State University, Baton Rouge, Louisiana. Benz, G. W. and R. P. Jacobs. 1986. Practical field methods of sexing largemouth bass. Progressive Fish Culturist 48:221 225. Block, B. A., H. Dewar, T. Williams, E. D. Prince, C. Farwell, and D. Fudge. 1998. Arc hival tagging of Atlantic bluefin tuna ( Thunnus thynnus thynnus ). Marine Technology Society Journal 32(1): 37 46.

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148 BIOGRAPHICAL SKETCH Ge offrey H. Smith Jr. was born in Sarasota, Florida. He grew up in this same city, and s commercial grouper fishing vessel. The time spent with his parents on their vessel is what started a lifelong love of the sea. His interest with the ocean and all of its organisms grew as he did. Geoffrey became an avid fisherman and aquarist, who collec ted most of his own specimens. He attended Sarasota High School and graduated 2002. While in high school he spent the majority of his summer vacation volunteering for the Stock Enhancement Program at Mote Marine Laboratory. He continued this work for two s ummers after his high school graduation as a sub contractor. In the fall of 2002 Geoffrey began his undergraduate studies at New College of Florida. While at New College he worked as a lab assistant at the Pritzker Marine Biology Research Center. He also a cted as a teaching assistant for a number of classes and co taught a field course spatial mapping in an intertidal fish species. In 2006 he earned his B.A. in Marin e Biology. Upon graduating he continued to work at New College as a lab assistant at the Pritzker lab and for the chemistry department. In 2008, Geoffrey began work as a lab technician in both the Phlips lab and Murie/Parkyn lab in the Program for Fisherie s and Aquatic Sciences at the University of Florida. His work in the Murie/Parkyn lab lead to a position as a M.S. graduate assistant in the fall of 2008. His studies concentrated on non lethal sexing and sex ratio impacts on population dynamics in greater amberjack. Upon the completion of his masters research Geoffrey will begin a Ph.D. in Fisheries and Aquatic Sciences at the University of Florida, which will focus on early life history of common snook. Geoffrey plans to pursue a teaching and research pos ition at a small to

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149 moderate sized university where he will be able to work one on one with students while continuing to pursue his research interests.