<%BANNER%>

Microhabitat Relationships for Spotted Sunfish at the Anclote, Little Manatee, and Manatee Rivers, Florida

HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix: Sampling locations and...
 References
 Biographical sketch
 

PAGE 1

HABITAT RELATIONSHIPS FOR SPOTTE D SUNFISH AT THE ANCLOTE, LITTLE MANATEE, AND MANATEE RIVERS, FLORIDA By ANDREW C. DUTTERER A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

PAGE 2

Copyright 2006 by Andrew C. Dutterer

PAGE 3

This thesis is dedicated to the preservati on and sustainable management of Floridas aquatic resources.

PAGE 4

iv ACKNOWLEDGMENTS I thank my committee, Drs. Mike Allen and Tom Frazer, and Mr. Eric Nagid, for guidance throughout the prepar ation of this thesis. I thank Christian Barrientos, Jason Be nnett, Greg Binion, Matt Catalano, Steve Crawford, Jason Dotson, Kevin Johnson, Galen Kaufman, Vaughn Maceina, Vince Politano, Mark Rogers, and Nick Trippel for assistance in data collection. I thank Mark and Laura Stukey (Rays Ca noes), Mr. and Mrs. Don Bislich, and Mr. James Blincoe (Little Manatee River State Park) for their willingness to provide me access to private or limited-acc ess boat ramp facilities. I thank Dr. Mary Christman for her advice and suggestions concerning the statistical analyses of portions of my research. I thank the Southwest Florida Water Mana gement District for providing funding for this research. Most of all, I thank my parents (Carl and Mary Ann) for their continued support throughout all of my endea vors. I could not have asked for a better family.

PAGE 5

v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT.....................................................................................................................vi ii CHAPTER 1 INTRODUCTION........................................................................................................1 Background...................................................................................................................1 Objectives..................................................................................................................... 2 Study Locations............................................................................................................3 2 METHODS...................................................................................................................5 Approach and Sampling Units......................................................................................5 Spotted Sunfish Sampling.............................................................................................6 Habitat Measurement....................................................................................................8 Habitat-Specific Community Assessment..................................................................11 Statistical Analyses.....................................................................................................12 3 RESULTS...................................................................................................................14 Spotted Sunfish Habitat Utilization............................................................................14 Effects of Altered Stage/Fl ow on Habitat Availability...............................................17 Habitat-Specific Fish Community Analysis...............................................................18 4 DISCUSSION.............................................................................................................29 APPENDIX SAMPLING LOCATIONS AND COMMUNITY SUMMARY......................................40 LIST OF REFERENCES...................................................................................................44 BIOGRAPHICAL SKETCH.............................................................................................50

PAGE 6

vi LIST OF TABLES Table page 1 Mean and standard deviation (SD) of habitat parameters for utilized and available habitat intervals at Anclote River and Manatee River downstream and upstream sites. .........................................................................................................21 2 Mean and standard deviation (SD) of habitat parameters for utilized and available habitat intervals per season a nd year for Little Manatee River. ..............22 3 Mean and standard deviation (SD) of ha bitat parameters for adult, juvenile, and available habitat intervals at Anclote River and Manatee River downstream and upstream sites...........................................................................................................23 4 Mean and standard deviation (SD) of ha bitat parameters for adult, juvenile, and available habitat intervals per season and year at Little Manatee River..................24 5 Latitude and longitude coordinates for spotted sunfish sampling reaches at Anclote, Little Manatee, and Manatee Rivers, Florida. ..........................................40 6 Habitat-specific list of fish species collected from the Anclote (A), Little Manatee (L), Manatee upstream (U) and Mantee downstream (D) rivers...............41

PAGE 7

vii LIST OF FIGURES Figure page 1 Locations of the Anclote, Little Mana tee, and Manatee Rivers in relation to Tampa Bay along the Gulf Coast of Florida. ............................................................4 2 Hydrographs representing average daily stage (meters, mean sea level) data for the Anclote, Little Manatee, and Mana tee River downstream sites during the two-year study period. .............................................................................................25 3 Proportion of total habitat intervals per ri ver with habitat rema ining inundated (y axis) with incremental decline in average river stage (m, x axis). ..........................26 4 Box plots of fish species richne ss (y axis) for each system. ...................................27 5 Box plots of fish diversity (y axis) for each system. ...............................................28

PAGE 8

viii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Science HABITAT RELATIONSHIPS FOR SPOTTE D SUNFISH AT THE ANCLOTE, LITTLE MANATEE, AND MANATEE RIVERS, FLORIDA By Andrew C. Dutterer December 2006 Chair: Micheal S. Allen Major Department: Fisher ies and Aquatic Sciences Establishing river minimum flow and level (MFL) regulations to maintain ecosystem health is a top priority for Flor idas management agencies due to expanding human population size and water demand. The spotted sunfish Lepomis punctatus is sensitive to changes in river water levels a nd could potentially serve as an indicator for ecosystem health, within the context of water level fluctuation and management. I measured characteristics of habitat (i.e., current veloci ty, depth, substrate, cover abundance) utilized by spotted sunfish and co mpared them to overall available habitat within the stream margin environment to id entify patterns of habitat selection at three southwestern Florida Rivers (Anclote, Litt le Manatee, and Manatee). Multivariate Analysis of Variance (MANOVA) was used to test whether habitat metrics collectively differed between available and utilized habita ts. I assessed how fluctuations in river stage and flow could influence spotted sunfish habitat availability. I also assessed fish community richness and diversity patterns am ong the predominant habitat types within

PAGE 9

ix each system. All sampling o ccurred from November 2004 to March 2006 during fall and spring seasons. Overall, spotted sunfish tended to sel ect habitat having gr eater structural complexity than the average available habi tat. In many instan ces, spotted sunfish appeared to select large and fine woody debris habitats. However, I coll ected spotted sunfish from a variety of habitat types th rough the study, indicating that the species was somewhat general in its hab itat associations. I found few significant differences in habitat measures between juvenile and adult fish, suggesting that habitat associations were similar between the life stages. My simulations indicated that 0.3-meter reductions in averag e daily stage could reduce habitat availability for spotted sunf ish by up to 20% across systems. Overall, habitats utilized by spotted sunfish were more resilient to stage declines due to fish utilization of areas with deeper depths and more complex habitat than the average conditions. I found that fish richness tended to vary among ha bitat types at all systems, and relatively complex habitat such as w oody debris and aquatic plants frequently exhibited higher fish richness than le ss complex habitats such as sandbars. I conclude that the inundation of comple x habitat types is likely important for spotted sunfish, and even minor changes in the average daily stag e during fall and spring seasons could substantially reduc e overall availability of these habitat types. Habitats utilized by spotted sunfish also exhibited high total fish richness, suggesting that protection of complex habitats will benefit the fish communities of southwest Florida Rivers. Results of this study can serve to inform resource managers responsible for setting MFL regulations to aid in the prot ection of habitat for freshwater fishes.

PAGE 10

1 CHAPTER 1 INTRODUCTION Background Water allocation and the ability to reach a balance betwee n the needs of society and the natural environment ar e growing concerns among wa ter resource managers and stakeholders, especially within the state of Florida. One crit ical step in the protection of Floridas water resources is the implemen tation of Minimum Flows and Levels (MFL) for priority water bodies ( 373.042, Florida Statutes). The MFL policies facilitate the regulation of surface water diversion and ground water withdrawal such that variation in streamflow and surface water levels can sust ain the ecological integrity of each water body (373.042, Florida Statutes). Fisheries managers have noted that mainta ining high quality river fisheries in light of increases in human population and land development would be a major challenge (Peters 1982; Bass and Cox 1985; Tyus 1990). Anthropogenic modifications in streamflow and resulting habitat alterati on can strongly influence the abundance and composition of aquatic fauna (Cushman 1985; Irvine 1985; Schlosser 1985; Bain et al. 1988; Kinsolving and Bain 1993; Travnichek et al. 1995; Power et al. 1999). Stream fish community metrics and population dynamics have been correlated with water level and streamflow changes (Kelsch 1994; Raibley et al. 1997; Weyers et al. 2003). Bonvechio and Allen (2005) linked year-class strength of several Centrarchid species to seasonal variation in flow/stage for four Florida Rivers.

PAGE 11

2 The spotted sunfish Lepomis punctatus a member of the Centrarchidae family, is one of the most abundant species in native st ream fish assemblages of Florida rivers (Hubbs and Allen 1943; Bailey et al. 1954; McLane 1955), and ha s been shown to exhibit population responses to fluctuating flow and stage (Rogers et al. 2005). Rogers et al. (2005) found that spotted sunfish abundance wa s low following persistently low flow and stage conditions during the year prior to samp ling at the Ocklawaha River, Florida. They believed that spotted sunfish could serve as an indicator species for MFL regulation due to the apparent population responses to changing streamflow and stage. However, habitat associations of the spotte d sunfish remain largely uninvestigated. Studies have shown that structurally complex cover, su ch as woody debris (Anderson et al. 1978; Angermeier and Karr 1984; Benke et al. 1985; Lobb and Orth 1991) and aquatic macrophytes (Rozas and Odum 1988; VanderKooy et al. 2000) provide important forage and refuge locations for stream fish communities. Spotted sunfish have been observed to utilize dense vegetation and fallen trees al ong stream margins (McLane 1955), and diet analyses indicate that spotted sunfish feed on invertebrates associated with aquatic vegetation (VanderKooy et al. 2000) and subm erged snags (Benke et at. 1985). The inundation and availability of these habitat type s, often characteristic of stream margins and important to stream fish communities, can be strongly influenced by fluctuations in flow and stage (Bain et al. 1988). Objectives My objectives were to 1) identify habitat associations for juven ile and adult spotted sunfish relative to available habitat at the Anclote, Li ttle Manatee, and Manatee Rivers, 2) predict how changes in river stage/flow for each system would influence habitat availability for spotted sunfish, and

PAGE 12

3 3) identify habitat-specific fish commun ity composition for each river system. Findings will help guide the establishment of MFL regulations for each river, so habitats for spotted sunfish and the broader fish community can be protected. Study Locations This study included the Anclote, Little Mana tee, and Manatee Rivers of the central Gulf Coast of Florida (Figure 1). The Ancl ote River flows generally east to west and discharges into the Gulf of Mexico betw een the towns of Holiday and Tarpon Springs, Florida. The Little Manatee River discha rges into Hillsborough Bay, the westernmost portion of Tampa Bay, whereas th e Manatee River discharges in to the Gulf of Mexico at the southern region of Tampa Bay. Similar to the Anclote River, the Manatee and Little Manatee Rivers also flow from east to west with all rivers having relatively short distances (i.e., 20-40 km) between headwaters and river mouths. All rivers exhibit a sinuous, meandering channel typical of low gradient streams (Figure 1).

PAGE 13

4 Figure 1. Locations of the Anclote, Little Manatee, and Manatee Rivers in relation to Tampa Bay along the Gulf Coast of Florid a. Approximate locations of sample sites in each river are indicated by red arrows. Specific latitude and longitude coordinates of sampling site boundaries are provided in Table 5 of the Appendix.

PAGE 14

5 CHAPTER 2 METHODS Approach and Sampling Units Habitat selection has been de fined many ways in the litera ture, and it was important in this study to clearly define habitat sel ection as used here. Rosenfeld (2003, p. 954) advocated that [h]abitat selection (i.e., differential occupa ncy) occurs when an organism avoids a particular habitat (negative selection) or uses a habitat in great er proportion than its availability in the environment (positive selection). Habitat selection can be demonstrated if fish occur at higher densitie s in particular habita ts, or if fish occur at higher frequencies in pa rticular microhabitats to relative frequency of that microhabitat in the environment. My use of the term habitat selection refe rs to the differential utilization of habitat relative to its availabi lity within the environment. Thus the overall approach of my study was to evaluate the habitat selection of spotted sunfish by characterizing the overall available habitat conditions w ithin study locations and then to compare these data to habitat characteristics from which spotted sunfish were collected. During pilot sampling at each river, I obs erved available habitat types (e.g., woody debris, overhanging root wads, and aquatic macrophytes) interspersed throughout each river system. As the mix of habitat types typically occurs across a relatively small longitudinal stream distance (< 500 m), clus ter sampling was determined to be an appropriate sampling strategy (S chaeffer et al. 1990). Cluste r sampling entails selecting replicate sample areas that include all ava ilable habitat types, so that variation among sample areas (i.e., clusters) is relatively sma ll, but variation among systems (i.e., rivers) is

PAGE 15

6 relatively large. Within each river system I utilized longitudina l sections of river channel, referred to as a river reach, as my sampling replicate. Ri ver reaches were 500 m in length at each river, because this size in cluded all available habitat types present in each system. Three reaches were selected for sampling on the Anclote and Manatee Rivers, whereas at the Little Manatee River, I selected five reaches for sampling. During pilot sampling on the Little Manatee River I en countered two distinct zones of channel morphology. Within the upper zone of the sampling region, I found that the channel width typically ranged between 15 20 m. The downstream zone of the sampling region had a wider channel, typically between 30 50 m, and it tended to support a greater abundance of rooted aquatic vegetation along ba nks, presumably due to a lesser degree of shading by the adjacent riparian overstory. Th erefore, for Little Ma natee River I selected three reaches within the upper zone and two reaches within the downstream zone of the sampling region to more fully characterize the habitat types available within this system. I sampled spotted sunfish and stream fi sh communities at two geographically disparate locations on Manatee Ri ver. During the first year of the study, I sampled within reaches located upstream of Lake Manatee, whereas sampling during the second year was conducted below the Lake Manatee dam. The appendix (Table 5) provides the latitude and longitude coordinates of all sampling reaches. River stage and discharge (when available) for the study period were obtained for each system from T. Carson, U. S. Geological Survey. Spotted Sunfish Sampling Spotted sunfish were sampled between November 2004 and March 2006, with an emphasis placed on fall and spring sampling. T ypically, spring and fall seasons along the central Gulf Coast of Florida have relatively low rainfall compared to summer. Thus,

PAGE 16

7 streamflows within this regi on are likely to be near base flow conditions during spring and fall. My sampling during spring (March-May) and fall (November-December) was designed to evaluate habitat a ssociations for spotted sunfis h during relativel y stable and low flow conditions. I sampled the Anclote and Little Manat ee Rivers once each during fall and spring seasons from November 2004 to March 2006. In total, there were two fall samples and two spring samples for each of these rivers. The Manatee River upstream samples were collected during fall 2004 a nd spring 2005, whereas, the Manatee River downstream samples were collected during fall 2005 and spring 2006. Spotted sunfish were collect ed using boat electrofishing gear that consisted of a 4.6-m aluminum jon boat powered by a 50-horsepower outboard motor with bow mounted anode probes. I used electrical pow er output of 5-8 Amps pulsed DC current regulated through a model VI-A Smith-Root pulsator. Power was supplied by a Honda 5000-watt AC generator. My method of operating the electrofishing boa t utilized two field personnel, one to operate the boat and pulsator located near th e stern, and a second, located on the bow, to identify, collect, and measure spotted sunfish. For each reach, there were essentially two electrofishing transects, one conducted along each bank for the entire 500-m. Field personnel operated the electrofishing boat along each bank at a slow, but consistent speed to ensure that all portions of each bank re gardless of available habitat received equal effort. All electrofishing samples were c onducted during daylight hours, approximately between 7:00 am and 5:00 pm.

PAGE 17

8 Following visual identification of a spotte d sunfish, the location of each individual was marked, as precisely as possible, with eith er a bright orange flag, when proximity to shore or water depth permitted, or a bright or ange buoy tethered to an anchor. I made efforts to locate spotted sunfish intervals at the point where an individual was first seen within the electromagnetic field. If I suspected that substantial elec trotaxis or drifting had occurred by an individual, it was not used for habitat data collection. I measured each spotted sunfish to nearest mm total le ngth and classified individuals as adult ( 60 mm TL) or juvenile (< 60 mm TL) (Caldwe ll et al. 1957; Carlande r 1977). In the case that two or more individuals were located within a 0.5-m radi us of one another, I marked the multiple locations as at the most central point. Habitat Measurement For this study, a habitat interval refers to a cylindrical volume of water horizontally defined by a 1 meter radius centered on a mark ed spotted sunfish location, spanning the vertical distance from water surface to substr ate. My goal was to quantitatively describe the habitat characteristics pr esent within each interval. Habitat measurements included depth, distance from bank, predominant substr ate type, current velo city at 60% depth, large woody debris size category and abunda nce, aquatic macrophyte type and density, and cover penetration to the substrate (see below for expl anation of terms). Depth, distance from bank, and cover penetration were measured to the nearest decimeter. Current velocity was measured with a Model 2000 Marsh-McBurney Flowmate flowmeter. I used a Woody Debris Index (WDI), very similar to that outlined by Dolloff et al. (1993), to quantify aggreg ations of large woody debris within habitat intervals. Pieces of large woody debris we re categorized by cross-sectio nal diameter and counted. Large woody debris size categories were: (I) 510 cm in diameter, and (II) greater than 10

PAGE 18

9 cm in diameter. A single WDI score was cal culated for each interval using the following equation WDI = WD1 + 2(WD2) (1) where WD1 = count of woody debr is size (I), and WD2 = count of woody debris size (II). Pieces of woody debris having a cross-sectional diameter less than 5 cm were categorized as fine woody debris (FWD), and abundance of FWD was estimated visually as the percentage of the interval volume occ upied (PVO). The category FWD included overhanging terrestrial brush, root wads, a nd other small diameter woody structure. Aquatic macrophyte abundance was also estimated visually as percenta ge of the interval volume inhabited (PVI). To form a less specific descriptor of ha bitat cover complexity, I formulated a Habitat Complexity Index (HC I). The HCI combines propor tions of large woody debris counts, FWD abundance, and aquatic m acrophyte abundance for each interval. I standardized the habitat metr ics as a proportion of the maximum value for each parameter across all rivers and sampling dates. The sta ndardized metrics were combined to create the HCI for each interval as 80 90 8 2 10 1 FWDPVO PlantPVI WD WD HCI (2) where WD1 = count of woody debris size (I), WD2 = count of woody debris size (II), PlantPVI = percent of interval inhabi ted by aquatic macrophytes, and FWDPVO = percent of interval occupied by fine w oody debris. The denominators in equation 2 represented the maximum values across all syst ems and intervals, for standardization to proportions.

PAGE 19

10 Cover penetration (P) was measured as the percentage of interval depth occupied by all combined habitat metrics in relation to the stream surface. For example, plants and woody debris that reached to a depth of 1 m within a 2-m deep interval were assigned a penetration value of 50%. Penetration valu es were used to estimate loss of spotted sunfish habitat with declin e in river stage (below). Available habitat was measured along equa lly spaced transects perpendicular to streamflow within each stream reach, sim ilar to methods proposed by Simonson et al. (1994) and implemented by Wheeler and Allen (2003). For each habitat sampling event, the location of the first transect was locat ed downstream from the upstream boundary of a stream reach at a randomly generated dist ance between 0 and 100 m. Thereafter, each transect was progressively lo cated 100 m downstream from th e previous transect until a total of five habitat availability transect s were completed for each sampling reach. Two habitat availability intervals, centered one meter from each stream bank, were located along each transect line, and habitat parameters were measured in the same manner as for intervals utilized by spotted sunfish. Thus, av ailable and utilized habitats were measured at the same spatial scale. I used the habitat characteristics sampled from each river to predict how reductions in average river stage would influence habitat av ailability for spotted sunfish. I surmised that habitat availability and resiliency to changing water levels could be described by HCI L P D HA (3) where HA is the habitat availability for the in terval, D is the water depth in m, L is a simulated incremental decline in average stag e in meters, HCI is the habitat complexity index, and P is the cover penetration. I simu lated values of L ranging from 0 to 2 meters with 0.1-m increments. For each incremental decline in L, I estimated the proportion of

PAGE 20

11 habitat intervals P(HA) where HA would decl ine to zero. Thus, the value 1-P(HA) depicted the proportion of habitat interval s where some portion of cover remained inundated following each incremental 0.1-m declin e in river stage (L). I obtained values of 1-P(HA) separately for utilized and avai lable habitat intervals for each system, which assessed how habitats used by spotted sunfis h varied from the random habitat intervals regarding potential habitat loss. Habitat-Specific Community Assessment To address my third objective, I samp led fish communities at each river. I conducted habitat-specific community electrof ishing at the Anclote and Little Manatee Rivers during April and December 2005. Fo r the Manatee River, community sampling was conducted once at the upstream site du ring April 2005, and once at the downstream site during December 2005. My goals were to document species richness and diversity and identify potential differences in these co mmunity metrics with respect to differences in predominant habitat types, similar to L obb and Orth (1991). To formulate diversity values, I used Shannon-Wieners in dex of biological diversity: s i i ip p H1 2) (log ) ( where H = Shannon-Wiener index of biological diversity, s = number of species, and pi = proportion of total sample belonging to i th species. I used the same areas within each river for community sampling as with spotted sunfish sampling. The same boat mounted electrofishing gear was used for community sampling as for spotted sunfish sampling. I used 300-second electrofishing tran sects as sample replic ates for each habitat type. During each transect, the electrof ishing boat was maneuvered such that the electromagnetic field was maintained only near a single habitat type. I then progressively

PAGE 21

12 moved the boat from one patch of selected hab itat to another of the same type, and this technique was continued throughout the durati on of each transect. A minimum of four transects were collected for each habitat type at each river and community sampling event (i.e., season). All fish collected were id entified to species, tallied, and measured to the nearest millimeter total length on site. Any unidentifiable individuals were preserved on ice and later keyed to sp ecies in the laboratory. Statistical Analyses Habitat variables measured at each inte rval were highly non-normal due to the proportional and categorical scales of the data (e.g., PVI, WDI). I transformed all habitat values to the ranks in order to construct nonparametric multivariate analyses of variance (MANOVA). The MANOVAs tested the null hypothesis that the mean ranked habitat variables (flow, depth, WDI, FWD, PlantPVI) collectively di d not differ between utilized and available habitat intervals. The MANO VAs were constructed separately for each river with the following fixed effects: interval type (available vs. u tilized), season, year, and the interactions of these values. The eff ect reach(river) was used as a block effect to account for any variation explained among reaches which was expected to be low due to the cluster sampling design. The MANOVA anal yses were repeated for three levels of interval type (adult, juvenile, and available) to assess differences in habitat utilization between adult and juvenile life stages. I anal yzed data from each river separately for a total of eight MANOVA tests (four total sampli ng areas in the Anclot e, Little Manatee, and Manatee upstream and downstream, tw o MANOVA each). For the Manatee River sections, the year effect was not possible to evaluate because I sampled each section (upstream and downstream) in only one fall a nd spring, resulting in interval type and season as fixed effects. When significant effects were detected with the MANOVAs, the

PAGE 22

13 least squares means procedure (SAS 2002) wa s used to identify the effects that contributed to the differences. I used three-way analysis of variance (ANOV A) to test for differences in mean HCI scores between utilized and available habitat intervals at Anclote and Little Manatee Rivers. Fixed effects were interval type, y ear, and season as described above. I used a two-way ANOVA to test for differences in m ean HCI scores at Manatee River upstream and downstream locations with interval type and season serving as the fixed effects. Because I sampled Manatee River upstream a nd downstream reaches each during a single year, there was no fixed effect of year. To test for differences in mean species richness and diversity among predominant habitat types at Anclote a nd Little Manatee Rivers, I use two-way ANOVA. Fixed effects included habitat type and season. I used one-way ANOVA to test for differences in mean species richness and diversity among habitat types at both Manatee River sampling locations. Community samples we re conducted once at each location on the Manatee River. Thus, habitat type was the only fixed effect.

PAGE 23

14 CHAPTER 3 RESULTS Spotted Sunfish Habitat Utilization I collected habitat parameter measuremen ts at a total of 470 available and 915 utilized habitat intervals across all sampling lo cations. At Anclote River, I characterized 120 available intervals and 292 utiliz ed intervals. With regard to the utilized intervals at Anclote River, 178 were occupied adults and 114 by juveniles. At Little Manatee River, I characterized 210 available intervals and 473 utilized ( 329 adult and 144 juvenile) habitat intervals. At the Manatee River dow nstream site, I characterized 60 available and 72 utilized (60 adult and 12 juvenile) habitat intervals, and at the Manatee River upstream site, I characterized 80 available and 78 u tilized (52 adult and 26 juvenile) habitat intervals. The MANOVA analyses testing for differences in collective habitat variables between utilized and available intervals were significant for all rivers, but some riverspecific differences occurred. For the Ancl ote and Manatee downstr eam site, there were no significant interactions (all P > 0.25) but the interval effect was significant indicating that habitat variables where spotted sunfish were collected differed from the available interval habitat variables (Table 1). Spo tted sunfish were collected from areas with higher WDI and FWD than the available interval s at both systems (Table 1). Water depth was greater for utilized than available intervals at the An clote River (Table 1). The MANOVA for habitat data from the Manatee River upstream site indicated a significant two-way interaction (P = 0.034) between in terval types (availabl e vs. utilized) and

PAGE 24

15 season. This interaction was due to significant differences in utilized habitat WDIs between seasons and was of little importance fo r comparisons between interval types. For the Little Manatee River, I found a si gnificant three-way interaction between interval type (utilized vs. av ailable), season (spring and fall) and year (first and second) (P < 0.0001). This interaction occurred becau se significant relationships among interval types were not consistent for either season, between years (Table 2). For example, utilized versus available hab itat variables differed for depth, WDI, and FWD in the spring of 2006, whereas only depth differed between interval types in fa ll 2004 (Table 2). All other statistical tests did not indicate significant interactions between interval types and season or year (all P > 0.379). Generally, adult and juvenile size-classe s of spotted sunfish displayed similar habitat use patterns, and both size classes we re associated with structurally complex habitat. For the Anclote River and the Manatee River downstream site, the MANOVA exhibited a significant interval effect (both P < 0.0001) without any significant interactions (all P > 0.109). Both adult and juvenile spotte d sunfish utilized areas with high WDI and FWD relative to available inte rvals. However, intervals occupied by juveniles had significantly grea ter plant densities than intervals occupied by adults or available intervals (both P < 0. 057) at the Manatee River downs tream site (Table 3). No differences were detected between life stages at the Manatee upstream site (Table 3). Similar to the combined lif e stage analysis, I found a three-way interaction among interval type (juvenile, adult, available), se ason, and year at the Little Manatee River (Table 4) (P < 0.0001). This interaction occurred because juvenile spotted sunfish occurred in habitats that were intermediate between adult and available intervals, and

PAGE 25

16 these effects were most apparent in spring 2006 (Table 4). For example, adults were collected from intervals with deeper depths and higher WDI and FWD than the available intervals in spring 2006, but habitat where j uveniles occurred during directed sampling was intermediate to the these values for the spring 2006. The depth variable also differed between adult and availabl e habitat intervals during fall 2004, with depth being intermediate for habitats occ upied by juveniles (Table 4). Thus, the relationships of utilized and available habitat for juveniles a nd adults generally mirro red the relationships I observed when size-classe s were aggregated. My use of the HCI score indi cated that spotted sunfish we re usually associated with physical habitat having greater structural comple xity relative to that of the representative available habitat. The mean HCI scores fo r utilized versus available habitat were significantly greater (P < 0. 0001) at the Anclote (0.47 ve rsus 0.27), and the Manatee River downstream site (0.65 versus 0.20). The Manatee River upstream site showed an opposite relationship with HCI scores being hi gher for available (0 .48) versus utilized (0.34) intervals (P < 0.0001). Similar to the MANOVA for collective habitat variables, the three-way ANOVA for HCI sc ores showed a significant th ree-way interaction at the Little Manatee River (P < 0.0001), where HCI scores were higher for utilized than available intervals in the fall 2004 (0.47 vers us 0.33) and spring 2006 (0.44 versus 0.26, both P < 0.045). Thus, the use of HCI show ed the same relationships as the MANOVA using all habitat variables, where spotted s unfish utilized locations with higher habitat complexity than the more general availabl e conditions within most systems. The Manatee River upstream site differed from th e other systems and showed some opposite

PAGE 26

17 patterns, but this likely occu rred because of the more hom ogenous nature of the habitat conditions at this site. Effects of Altered Stage/Flow on Habitat Availability My study rivers are located in Southwest Fl orida, where rainfall patterns consist of a summer wet season with a relatively dry spri ng, winter, and fall (Kel ly et al. 2005). My study design sampled these rivers in spring a nd fall during periods when river flow and stage are relatively low. Water levels dur ing our sampling were similar between years (Figure 2) and representative of the averag e, relatively low flow conditions expected during these seasons. However, all of my study reaches except the Manatee River upstream were tidally influenced and exhibi ted stage variation of about 0.3 meters throughout the day. Flow direction varied from downstream to occasionally upstream with outgoing and incoming tides. Nevertheless all of the study sites had low salinity (< 5 ppt) throughout this study as indicated by my collection of obligate freshwater fishes on all sampling events and the ability to use a freshwater electrofishing arrangement as the sampling gear. Simulations of HA indicated that average st age declines of 0.3 m could result in 0 to 20% habitat loss for spotted sunfish across systems (Figure 3). The Southwest Florida Water Management District has used a criter ion of 15% habitat loss as significant for coastal rivers (Kelly et al. 2005), and my simu lations indicated that this degree of habitat loss would occur with average stage declines of 0.3 m or less in three of four systems. The largest decline in available habitat occu rred at the Manatee River downstream site and the smallest at the Manatee River upstream site (Figure 3). The Anclote and Little Manatee Rivers exhibited about 20% losses in habitat availability with a 0.3 m reduction in average stage, and 40-50% habitat loss w ith a 0.6 m reduction. The Manatee River

PAGE 27

18 upstream site was characterized by relatively steep banks and abundant aquatic plants (primarily Maidencane Panicum hemitomon ) extending out to 1-2 m water depths, which made habitat loss less susceptible to changes in water levels. For the other three systems, a 0.3 m decline in average stage was pred icted to reduce availa ble habitat by 15-20% (Figure 3). Spotted sunfish utilized habitat intervals that were more resilient to changes in river stage than the average condition at all rive rs except the Manatee River upstream site. Utilized habitat intervals exhibited more grad ual declines in habita t availability with incremental declines in average stage at the Anclote, Little Manat ee, and Manatee River downstream site (Figure 3). This occurred because spotted sunf ish utilized intervals that were deeper and had more complex habitat th an the available habitat intervals at each system. The Manatee River upstream site exhib ited little difference in habitat availability between utilized and available intervals, a nd slightly lower habitat loss for available intervals at a 0.6 m average st age decline (Figure 3). Because this site was located above the impoundment, the habitat conditions (e.g., fl ow, stage, HCI) were likely influenced by the dam, resulting in habita t relationships that were not similar to our other study sites or other southwest Florida st reams. All other stream sites in this study exhibited relatively rapid habitat loss with declines in average stage. Habitat-Specific Fish Community Analysis Over the course of this study, I collected 23 fish species at the Anclote River, 26 at the Little Manatee River, 12 at the Mana tee River upstream and 21 species at the Manatee River downstream. Collectively, there were 26 species collected from the Manatee River system. Thus, overall fish species richness was similar among river systems and ranged from 23 to 26. Individua l fish species and the habitats from which

PAGE 28

19 they were collected within each river are s hown in the Appendix (Table 6). The family Centrarchidae was the most common family w ith eight species (Appendix, Table 6). As expected for these coastal systems, fish taxa represented a range of obligate freshwater (e.g., Centrarchidae) to estuar ine species (e.g., common snook Centropomus undecimalis Appendix, Table 6). I found seasonal patterns in species richne ss at the Anclote and Little Manatee Rivers, and diversity varied with season at th e Anclote River. At both rivers, the season and habitat effects were significant (all P < 0. 05) for species richness, and the interaction of season and habitat was not significant (both P > 0.13), al lowing evaluation of only the main effects. Mean richness was higher in the fall (6.3 and 6.3 species per transect) than in the spring (3.3 and 3.7 species per transe ct) at the Anclote and Little Manatee Rivers, respectively (all P < 0.05). Mean diversity wa s higher in the fall (2. 13) than in the spring (1.38) at the Anclote River. However, m ean diversity did not vary between seasons at the Little Manatee River (P = 0.17). I also detected differences in richness among habitats at two of the three river systems. For the Anclote River, overhanging terrestrial brush, exposed root-wads, and large woody debris had greater mean species richness (all P < 0.1, Figure 4) and diversity than sandbar habitat (all P < 0.1, Figure 4). Thus, it appeared that all complex habitat types contained higher richness and diversity th an sandbar habitats at the Anclote River. At the Little Manatee River, aquatic plants contained higher mean richness than large woody debris and overhanging terrestrial brus h (both P < 0.02, Figure 4), but the other habitat types did not differ with regard to ri chness. Fish diversity at the Little Manatee River did not differ among habitat types (P = 0.29, Figure 5).

PAGE 29

20 For the Manatee River, I found no differen ces in fish richne ss or diversity among habitat types at the Manatee River upstream site (Figures 4 and 5, both P > 0.6), but species richness was higher in large woody debris than the ot her habitats for the Manatee River downstream site (P = 0.04, Figure 4). Fish diversity did not differ among habitat types at either Manatee River site (both P > 0.51, Figure 5). My habitat-specific electrofishing revealed several differences in fish richness, whereas fish diversity varied wi th habitat only at the Anclote Ri ver. In general, relatively complex habitat such as large woody debris and plants frequently harbored higher fish richness than less complex habitats such as sandbars. The nearly homogeneous habitat characteristics at the Manat ee River upstream site probably contributed to the lack of significant differences for this system.

PAGE 30

21 Table 1. Mean and standard deviation (SD) of habitat parameters for utilized and available habitat intervals at Anclot e River and Manat ee River downstream and upstream sites. Depth is stream dept h in m, Current is current velocity in m/s, WDI is woody debris index, FWD is percent of interval volume occupied by fine woody debris, and Plant is per cent of interval vo lume inhabited by aquatic macrophytes. Shaded blocks denote significant differences, as indicated by MANOVA test ing and comparison of least squares means, between utilized and ava ilable habitat intervals fo r the corresponding habitat parameter (All P < 0.1). River Parameter Utilized x(SD) Available x(SD) Depth 1.00(0.57) 0.83(0.45) Current 0.01(0.01) 0.01(0.02) WDI 3.22(3.16) 1.60(2.50) FWD 17.84(13.59) 11.08(10.67) Anclote Plant 0.89(3.19) 1.58(6.22) Depth 0.71(0.30) 0.67(0.31) Current 0.00(0.00) 0.00(0.00) WDI 5.94(5.14) 1.15(2.51) FWD 13.19(7.28) 7.00(5.61) Manatee downstream Plant 1.53(3.99) 1.50(5.77) Depth 1.67(0.71) 1.69(0.70) Current 0.00(0.00) 0.00(0.00) WDI 0.64(1.46) 0.60(1.28) FWD 6.92(7.78) 9.88(13.64) Manatee upstream Plant 18.46(13.96) 27.75(23.87)

PAGE 31

22Table 2. Mean and standard deviation (SD) of habitat parameters for utilized and av ailable habitat intervals per season and yea r for Little Manatee River. Depth is stream de pth in m, Current is current velocity in m/s, WDI is woody debris index, FWD is percent of interval volume occupied by fine woody debris, and Plant is percent of interval volume i nhabited by aquatic macrophytes. Shaded blocks denote signi ficant differences, as indicated by M ANOVA testing and comparison of least squares means, between utilized and av ailable habitat intervals for the corr esponding habitat parameter (All P < 0.1). First Second Fall Spring Fall Spring Parameter Utilized x(SD) Available x(SD) Utilized x(SD) Available x(SD) Utilized x(SD) Available x(SD) Utilized x(SD) Available x(SD) Depth 0.89(0.47) 0.65(0.44) 0.88(0.51) 0.86(0.48) 0.75(0.41) 0.73(0.52) 0.76(0.37) 0.55(0.33) Current 0.04(0.05) 0.03(0.05) 0.06(0.07) 0.05(0.06) 0.04(0.04) 0.04(0.04) 0.01(0.02) 0.01(0.02) WDI 2.49(3.54) 1.28(2.08) 1.39(1.92) 1.24(1.84) 1.69(2.64) 0.88(1.35) 2.76(3.50) 1.00(1.48) FWD 16.37(18.27) 10.75(13.09) 13.51(13.09) 12.14(11.66) 10.09(12.01) 10.00(9.69) 14.26(12.92) 9.80(12.86) Plants 6.59(13.39) 8.25(18.10) 5.64(8.50) 6.29(14.26) 8.32(11.76) 3.80(6.97) 4.56(10.03) 5.00(10.93)

PAGE 32

23 Table 3. Mean and standard deviation (SD) of habitat parameters for adult, juvenile, and available habitat intervals at Anclot e River and Manat ee River downstream and upstream sites. Depth is stream dept h in m, Current is current velocity in m/s, WDI is woody debris index, FWD is percent of interval volume occupied by fine woody debris, and Plant is per cent of interval vo lume inhabited by aquatic macrophytes. Shaded blocks a nd differing letters denote significant differences, as indicated by MANOVA testing and comparison of least squares means, among interval types (All P < 0.1). River Parameter Adult x(SD) Juvenile x(SD) Available x(SD) A A B Depth (m) 1.04(0.58) 0.95(0.55) 0.83(0.45) A BC AC Current (m/s) 0.011(0.02) 0.006(0.01) 0.011(0.02) A B C WDI 3.43(3.23) 2.89(3.04) 1.60(2.50) A A B FWD (PVI) 17.30(13.72) 18.68(13.40) 11.08(10.67) A A A Anclote Plant (PVI) (0.67)2.51 (1.23)4.02 1.58(6.22) A A A Depth (m) 0.73(0.30) 0.64(0.25) 0.67(0.32) A A A Current (m/s) 0.00(0.00) 0.00(0.00) 0.00(0.00) A A B WDI 6.05(5.05) 5.42(5.78) 1.15(2.51) A A B FWD (PVI) 13.50(7.32) 11.67(7.18) 7.00(5.61) A B A Manatee downstream Plant (PVI) 1.00(3.03) 4.17(6.69) 1.50(5.77) A A A Depth (m) 1.57(0.66) 1.86(0.79) 1.69(0.70) A A A Current (m/s) 0.00(0.00) 0.00(0.00) 0.00(0.00) A A A WDI 0.77(1.60) 0.38(1.10) 0.60(1.28) A A A FWD (PVI) 8.08(8.41) 4.62(5.82) 9.88(13.64) A A A Manatee upstream Plant (PVI) 16.92(13.07) 21.54(15.41) 27.75(23.87)

PAGE 33

24Table 4. Mean and standard deviation (SD) of habitat parameters for adult, juvenile and available habitat intervals per seaso n and year at Little Manatee River. Depth is stream depth in m, Current is current velocity in m/s, WDI is woody debris index, FWD is percent of interval volume occupied by fine woody de bris, and Plant is percent of interval volume inhabited by aquatic macrophytes. Shaded blocks and differing letters de note significant differences, as indicated by MANOVA testing and comparison of least squares means, among interval types (All P < 0.1).

PAGE 34

25 Figure 2. Hydrographs represen ting average daily stage (meters, mean sea level) data for the Anclote, Little Manatee, and Mana tee River downstream sites during the two-year study period. Sampling periods at each system are indicated by red arrows. Stage data were provide by T. Carson, U. S. Geological Survey.

PAGE 35

26 Figure 3. Proportion of total habitat interval s per river with hab itat remaining inundated (y axis) with incremental decline in av erage river stage (m, x axis). Dotted lines show habitat intervals utilized by spotted sunfish, and solid lines show randomly located intervals representing ove rall available habitat. The dashed red line signifies the 15% habi tat loss value at each system

PAGE 36

27 Figure 4. Box plots of fish species richne ss (y axis) for each system. Habitat types including overhanging terrest rial brush (OTB), roots, sandbars (SB), large woody debris (LWD), and aquatic plants (Plants) are shown (x axis). Observations are from habitat-specific electrofishing transects. Differential lettering denotes significant differe nce in group means, as indicated by ANOVA testing and comparison of least squares means, among habitat types (All P < 0.1). Median values are deno ted by the horizontal mid-line within the shaded region of each box. Uppe r and lower bounding hor izontal lines of the shaded region of each box denote the 75th and 25th percentile values. Upper and lower box plot whiskers denote the 90th and 10th percentile values. Dots lying beyond box plot whiskers denote the 95th and 5th percentile values.

PAGE 37

28 Figure 5. Box plots of fish diversity (y axis) for each system. Habitat types including overhanging terrestrial brush (OTB), r oots, sandbars (SB), large woody debris (LWD), and aquatic plants (Plants) are s hown (x axis). Observations are from habitat-specific electrofishing transect s. Differential lettering denotes significant difference in group means, as indicated by ANOVA testing and comparison of least squares means, among habitat types (All P < 0.1). Median values are denoted by the hori zontal mid-line within the shaded region of each box. Upper and lower bounding horizontal line s of the shaded region of each box denote the 75th and 25th percentile values. Upper and lower box plot whiskers denote the 90th and 10th percentile values. Dots lying beyond box plot whiskers denote the 95th and 5th percentile values.

PAGE 38

29 29 CHAPTER 4 DISCUSSION Spotted sunfish generally selected hab itats with greater habitat complexity compared to overall available habitat conditi ons. Woody debris habita ts were frequently selected by spotted sunfish, and the associa tion with these habitats was the most common of any of the habitat relationshi ps that I measured. I also found spotted su nfish utilizing aquatic plants as a habitat when plants were present and one instance of juveniles selecting habitats of greater plant abundance relative to adults Overall, spotted sunfish appeared to be habitat generali sts, with fish selecting areas of more complex habitat than the available intervals (i.e., woody debris and/ or aquatic plants). This generalist use of habitat corresponds to several anecdotal repor ts that associate spotted sunfish with a variety of habitats within Florida st reams (Chable 1947; Kilby 1955; McLane 1955; Caldwell et al.1957) and is evident among othe r ecologically similar Florida Centrarchid species. Hill and Cichra (2005) noted that the congeners such as warmouth sunfish L. gulosus redbreast sunfish L. auritus and dollar sunfish L. marginatus have been historically collected from a variety of lotic environments, and they described all of these species as having been associated with woody debris, aquatic vegetation, and other structurally complex habitat types. Numerous investigators have noted the importance of woody debris habitats to fish in lotic environments (Todd and Rabeni 1989; Fausch and Northcote 1992; Everett and Ruiz 1993; Koehn et al. 1994; Flebbe and Dolloff 1995; Crook and Robertson 1999; Horan et al. 2000; Dolloff and Warren 2003). W oody debris habitat offers refuge from

PAGE 39

30 current velocity (McMahon and Hartman 1989; Shirvell 1990) and predators (Koehn et al. 1994), and provides foraging (Benke et al. 1984; Smock et al. 1985) and ambush locations for stream fishes (Matthews 1998). The current velocity measurements that I recorded throughout the study were generally very low (range: 0 0.4 m/s), indicating that refuge from flow velocity would likely have been a minor fact or in spotted sunfish habitat use. The body form and mouth mor phology of spotted sunfis h suggest that the species is most suited to feeding on small pr ey items attached to substrate or drifting within the water column (Ca rrol et al. 2004). Thus, it is much more likely that the association of spotted sunfish with woody debris and complex ha bitats was attributable to their use of these habitat types as foraging area s and refuge from predation rather than as velocity refuge. However, during higher flows they may utilize woody debris as velocity refuge. Previous work surrounding the feeding ecology of spotted sunfish provides a functional linkage between the species and co mplex habitats such as woody debris and aquatic vegetation. As implied by their general morphology and relatively small size, spotted sunfish feed primarily on aquatic in sects and other invert ebrates (Chable 1947; McLane 1955; Caldwell et al.1957). Chab le (1947) and McLane (1955) found 100% and 85% of their spotted sunfish diet samples, re spectively, to contain insects. Prey taxa frequently observed among spotted sunfish di et items include chironomidae, coleoptera, trichoptera, ephemeroptera, and amphipoda (Chable 1947; McLane 1955; Caldwell et al.1957), all of which have been shown to be associated with complex habitats in Florida streams (Warren et al. 2000; Steigerwalt 2005).

PAGE 40

31 Across nearly all lotic environments, w oody debris has been shown to provide important habitat for aquatic invertebrates (Braccia and Batzer 2001; Benke and Wallace 2003). However, because of the general instab ility of sand and mud substrates in these systems, the relative value of woody debris root wad, and submerged vegetation to stream ecosystems appears to increase in lo wland rivers where these habitats offer the most stable attachment sites for invertebra tes (Benke et al. 1984; Smock et al. 1985. Benke et al. (1985) showed that invertebrate communities derived from snag habitat were a valuable source of prey items for Lepomis spp. and other stream fishes at Satilla River, Georgia, and noted that snag fauna comprised at least 60% of diet composition for all Lepomis spp., including spotted sunfish. Kelly et al. (2005) noted a similar linkage between snag and root habitat derived inve rtebrate communities and redbreast sunfish diet composition at the Alafia River, Fl orida. Caldwell et al. (1957) found large quantities of periphyton among spotted sunf ish stomachs and indicated that it was representative of the attach ed algal community growing on leaves of locally abundant Sagittaria at the Silver River, Florida. They suggested that the pe riphyton were most likely incidentally consumed while feed ing on attached invertebrates among these vegetation beds. McLane (1955) also found f ilamentous algae to be a large component (26.9 % by occurrence) of s potted sunfish diet at the St. Johns River, Florida. Complex habitat such as woody debris and aquatic vegetation also provides refuge from predators for juvenile or small bodied fishes such as Lepomis spp. (Savino and Stein 1982; Everett and Ruiz 1993; Crook and R obertson 1999; Dolloff and Warren 2003). Juvenile bluegill sunfish tend to select complex habitats (i.e., aquatic plants or artificial aquatic plants) in the presence of potential predator s and this behavior often results in

PAGE 41

32 reduced predation success (Savino and Stein 1982; Werner et al.1983; Gotceitas and Colgan 1987; Johnson et al.1988). Because the coastal rivers of Flor ida contain a variety of freshwater and marine piscivores, and spot ted sunfish remain relatively small even as adults, the availability of complex habitat is probably important as refuge from predation. Largemouth bass and/or common snook were abundant in all our sample rivers, and loss of complex habitat would likely expose spot ted sunfish to higher mortality rates via predation (e.g., Savino and Stein 1982). Habitat requirements of adu lts and juveniles of a speci es often differ (Larkin 1978; Werner and Gilliam 1984; Halper n et al. 2005). Ontogenetic sh ifts in habitat utilization have been observed among various lotic fishes, such as Roanoke logperch Percina rex (Rosenberger and Angermeier 2003), river blackfish Gadopsis marmoratus (Koehn et al. 1994), creek chub Semotilus atromaculatus (Magnan and FitzGera ld 1984), and several Salmonid species (Moore and Gregory 1988; McMahon and Hartman 1989; Nickelson et al. 1992). I identified one inst ance of juvenile spotted sunfis h using greater aquatic plant densities relative to adults. However, the general pattern was that adult and juvenile spotted sunfish occupied similar habitat t ypes, and I found few significant differences between habitat parameters collected for a dult and juvenile lifestages. The overall similarity in adult and juvenile spotted sunf ish habitat utilization patterns corresponded to McMahons (1984) description of habitat us e of a congener, warmouth sunfish. Mittlebach (1984) noted that pumpkinseed sunfish L. gibbosus tend to occupy similar habitat types throughout their ontongeny, but overall few studies have specifically addressed comparisons of hab itat utilization between adult and juvenile lifestages of Lepomis spp. (see Hill and Cichra 2005).

PAGE 42

33 Although it represents a single occurrence in my results, the use of higher plant densities by juveniles relative to adults is not surprising. Lobb and Orth (1991) also found associations of juvenile stream fish sp ecies with in-stream ve getation. Similarly, Hellier (1966) observed a pattern in use of ve getation by juvenile redbreast sunfish in a Florida river. Juvenile blue gill sunfish have been observe d using complex habitats that offer abundant and relatively small intersti tial spaces, much like those created by dense aquatic vegetation, as a refuge from pred ation (Savino and Stein 1982; Werner et al. 1983; Gotceitas and Colgan 1987; Johnson et al. 1988). At Anclote and Little Mana tee Rivers, I found that habi tat intervals occupied by spotted sunfish exhibited greater depth values re lative to the available habitat intervals. The outer edge of stream bends typically co rresponded to areas of greater depth found in close proximity to the bank, and these locati ons may provide an important component of spotted sunfish habitat. These areas would be subjected to greater substrate erosion during periods of increased streamflow; thus creating localized abundances of exposed root-wads and fallen woody debris. Deeper areas along the bank may also be more resilient to fluctuations in river stage, thus, providing habitat that remains inundated throughout daily tidal changes. My identification of spotted sunfish hab itat selection was likely largely dependent on changes in density of the species across ha bitat types. Van Horn e (1983) stressed that the assumption that greater density of a species within a particular habitat type translates into greater quality of that habitat type ma y not always hold true. Evaluation of habitat quality should consider spatial changes in species density, but it must also consider comparisons of survival and reproductive contribution by individuals occupying differing

PAGE 43

34 habitats (Van Horne 1983). For example, so cial interactions am ong individuals of a species may create instances where subdomina nt individuals, exhibiting reduced survival and reproductive output relativ e to dominant individuals, oc cupy sub-optimal habitats at high densities (population sink). In this situation, sustenan ce of the local population may be reliant upon a few dominant individuals, exhibiting high su rvival rate and reproductive output, that occupy the best hab itat (population source) at a re latively low density. Thus, relying solely on abundance as an indicator of habitat quality may lead to erroneous conclusions in the identification of quali ty habitats (Van Horne 1983). My study addressed patterns in habitat use and selection by spotted sunfish in Florida Rivers, but I did not investigate demographic patterns such as individual survival rates or reproductive contribution in relation to stream habitat t ypes. Thus, although my identification of utilized and selected habitat characteristics may be representative of important or required spotted sunfish habita t, the habitat associations revealed here may not infer differences in fish survival and growth had these habitats been lost from the system. Experimental manipulations would be required to elucidate the impacts of habitat change on fish vital rates. Rogers et al. (2005) found that spotted s unfish abundance was positively related to river stage at the Ocklawaha Ri ver, Florida, with high fish abundances in years following high stage the previous year. I did not evaluate inter-annua l trends in spotted sunfish abundance in this study, but the habitat use and selections patterns th at I identif ied help explain the mechanisms for the relationship re ported by Rogers et al (2005). High water levels inundate complex habitats, likely provi ding food and refuge for spotted sunfish. Conversely, years with low water levels would reduce habitat av ailability possibly

PAGE 44

35 leading to lower spotted sunfish abundan ce via food limitation, predation, or a combination of these factors. Bonvechio and Allen (2005) found th at redbreast sunfish year class strength was also positively rela ted to river flows in Florida, and the relationship for Lepomis spp. may extend across several members of the genus. My simulations indicated that relatively sm all decreases in river stage (e.g., average 0.30 m decline) below base-flow conditions coul d result in up to 20% reduction in habitat availability. Kelly et al. (2005) identified MFL strategies fo r the Alafia River, Florida, based on periods of varying seasonal flow s through the year. My samples were conducted during their Blocks 1 and 3, wh ich represent the spring and fall seasons typically exhibiting relatively low flows and stage. Water levels and flows during my sampling events were relatively low at about base-flow conditions (r efer to Figure 2). My habitat measurements suggested that rela tively minor declines in average river stage at base flow conditions c ould reduce overall habitat availability beyond the 15% benchmark used by the Southwest Florida Water Management District to signify undesirable resource loss (Kelly et al. 2005). However, these habitat loss simulations may not accurately reflect changes in shorel ine habitat availabil ity during long term (multi-year) stage and streamflow declines. Long term decreases in flow regime would redefine stream margins in response to new water level trends, and riparian vegetation would colonize newly exposed banks, thus, allowing for continued recruitment of complex habitats derived from terrestrial so urces. Furthermore, long term changes in river stage and steamflow trends may provi de conditions conduciv e to aquatic plant colonization, also creating new complex habita ts for stream fishes. Considering these

PAGE 45

36 limitations, I advocate that my simulations are li kely best suited to estimate habitat loss during short-term (< 1-2 years) declines in average daily stage. I did not evaluate the potentia l effect of low river flow and stage on habitat loss via saltwater intrusion. Stream channel elev ation was relatively low within all of my sampling reaches, and with the exception of those on the Manatee River upstream of the Lake Manatee Dam, many of my sampling r eaches were at least somewhat tidally influenced. It is possible, under conditions of persistent low freshwater discharge, that water level in my study areas would remain stable if saline water from the downstream estuary encroached upstream, resulting in a diffe rent form of habitat loss for freshwater fish communities than I measured. Catala no et al. (2006) found sa ltwater intrusion to significantly reduce available habitat for fr eshwater fishes in the Lower Hillsborough River, Florida when flows declined. Es tevez and Marshall (1994) noted changes in historical isohaline and vege tation patterns in the Manatee River estuary following implementation of flow regulation via a dam on the Manatee River, Florida. I did not find high salinity waters in the Anclote, Li ttle Manatee, or Manatee downstream sites during this study, with freshwater fishes pr esent during all sampli ng events. However, location and movement of isohalines within th e shallow bays and lagoons of the Gulf of Mexico are considered especially susceptible to the effects of fluctu ating freshwater flow inputs (Sklar and Browder 1998). Therefore, sa ltwater intrusion shoul d be considered as another potential form of hab itat loss for freshwater/oligoha line fishes in these coastal river systems, and defining the extent of poten tial saltwater intrusion is needed for these systems.

PAGE 46

37 My sampling design incorporated sampling along the bank of each river, and it is possible that mid-channel habitat could have influenced habitat availability for spotted sunfish. However, these rivers are relative ly shallow (< 2 meters ) and narrow (i.e., < 50 meters wide) with shifting of sediments occurring during high flood events. The mid channel areas of the rivers were largely devoid of woody debris and aquatic plants. Nevertheless, my evaluation of habitat availa bility for spotted sunfish should be viewed as conservative, as not all sections of the ri vers were sampled for habitat availability and fish occurrence. My habitat-specific community sampling indicated that not only are complex habitat types selected for by spotted sunfish but that they tend to harbor greater species richness relative to other ha bitat types as well. Fish species richness varied among habitat types for all sampling rivers except the Manatee River upstream site. The specific habitat types that contained the highest fi sh richness varied among rivers, but fish richness was generally highest in either la rge woody debris (Anclote River and Manatee River downstream) or plant habitats (Little Mana tee River). These results were similar to those of Lobb and Orth (1991), who found highest stream fish densities in and adjacent to snags relative to other habitats in a warmwa ter Virginia stream. Rogers et al. (2005) found that spotted sunfish abundance was rela ted to fish richness across years at the Ocklawaha River, Florida. The habitat relationships I identi fied supported this relationship because both spotted sunfish o ccurrence and total richness were highest in the complex habitats at each system. I was una ble to detect differences in fish diversity among habitat types in most cases, suggesting th at fish diversity may be a less effective metric for detecting change in fish communities than species richness.

PAGE 47

38 I acknowledge that my use of electrofish ing as a sampling technique may introduce some inherent biases into data collected fo r spotted sunfish habita t intervals (e.g., Bain and Finn 1991). Efficacy of electrofishing is in versely related to dept h and complexity of some habitat types (i.e., dense vegetation) (Bayley and Austen, 2002). These tendencies may have biased locations of spotted sunfis h toward areas of shallower depth and away from areas of dense aquatic plants or overha nging brush. However, I directed sampling effort along river banks to minimize the eff ects of depth on capture efficiency. When subjected to an electromagnetic field, fish may exhibit varied responses. Of some concern were positive electrotaxis, the movement of a fish toward the electrofisher anode, negative electrotaxis, and fright response, the latter two of which would result in movements of a fish away from the electr ofisher electromagnetic field (Bain and Finn 1991; Reynolds 1996). Any of these results coul d have affected the spatial accuracy of spotted sunfish habitat intervals. However, I made efforts to locate spotted sunfish intervals at the point where an individual was first seen with in the electromagnetic field. If I suspected that substantial electrotaxis had occurred by an individual, it was not used for habitat data collection. Additionally, I felt that use of a one meter radius for habitat intervals provided sufficient volume of measured habitat that it would remain representative of an individual s true habitat occurrence if limited electrotaxis did occur. Electrofishing efficiency also increases w ith fish size (Reynold s 1996), suggesting that juvenile spotted sunfish were likely not collected as effici ently as adults. However, because my goal was to measure the habitat associations, the relative comparisons among habitat types at each sy stem were meaningful.

PAGE 48

39 In summary, I identified habitat use and selection patterns for spotted sunfish but found them to be fairly general in their hab itat associations. Few differences were found between adult and juvenile ha bitat use patterns, indicating that the generalist use of habitats likely persists th roughout spotted sunfish ontongeny. My results suggest that seemly minor changes in the average stage during fall and spring seasons may substantially reduce the availability of habita ts used by spotted sunfish. Spotted sunfish appeared to be a good indicator of fish richness differences among habitat types, suggesting that protection of co mplex habitats will also bene fit the whole fish community in southwest Florida Rivers.

PAGE 49

40 APPENDIX SAMPLING LOCATIONS A ND COMMUNITY SUMMARY Table 5. Latitude and longitude coordina tes for spotted sunfish sampling reaches at Anclote, Little Manatee, and Manatee Ri vers, Florida. Upstream refers to upstream reach boundaries and Downstream refers to downstream reach boundaries. River Reach Upstream Downstream 1 N 28.382 W 82.527 N 28.311 W 82.656 2 N 28.270 W 82.660 N 28.199 W 82.803 Anclote 3 N 28.167 W 82.806 N 28.946 W 82.826 1 N 27.531 W 82.523 N 27.673 W 82.768 2 N 27.569 W 82.787 N 27.569 W 82.010 3 N 27.536 W 82.012 N 27.435 W 82.214 4 N 27.097 W 82.411 N 27.956 W 82.350 Little Manatee 5 N 27.898 W 82.430 N 27.888 W 82.691 1 N 27.887 W 82.973 N 27.997 W 82.171 2 N 27.987 W 82.186 N 27.077 W 82.468 Manatee upstream 3 N 27.089 W 82.490 N 27.109 W 82.666 1 N 27.779 W 82.431 N 27.964 W 82.546 2 N 27.023 W 82.631 N 27.275 W 82.679 Manatee downstream 3 N 27.323 W 82.637 N 27.563 W 82.683

PAGE 50

41Table 6. Habitat-specific list of fish species collected from the Anclote (A), Little Manatee (L), Manatee upstream (U) and Ma ntee downstream (D) rivers. Roots Snags Overhanging Brush Plants Sandbars Family Species A L D A L U D A L U D L U A L D Florida gar Lepisosteus platyrincus x x x x x x x x x x x x Lepisosteidae Longnose gar L. osseus x x x x x x x x Amiidae Bowfin Amia calva x x x x x x Anquillidae American eel Anguilla rostrata x x x x Synbranchidae Asian swamp eel Monopterus albus x x Golden shiner Notemegonus crysoleucas x x x x Taillight shiner Notropis maculatus x x x x Cyprinidae Coastal shiner N. petersoni x x x x x x x x x x x x x Catostomidae Lake chubsucker Erimyzon sucetta x x x Channel catfish Ictalurus punctatus x x Ictaluridae Brown bullhead Ameiurus nebulosus x x Clariidae Walking catfish Clarias batrachus x Bluefin killifish Lucania goodei x x x x x Rainwater killifish L. parva x Golden topminnow Fundulus chrysotus x Fundulidae Seminole Killifish F. seminolis x x x

PAGE 51

42 Roots Snags Overhanging Brush Plants Sandbars Family Species A L D A L U D A L U D L U A L D Gambusia sp. x x x x x x x x x x x x Poeciliidae Sailfin molly Poecilia latipinna x x x x x Banded pygmy sunfish Ellasoma zonatum x Ellasomatidae Everglades pygmy sunfish E. evergladei x Largemouth bass Micropterus salmoides x x x x x x x x x x x x x x Bluegill sunfish Lepomis macrochirus x x x x x x x x x x x x x x x Dollar sunfish L. marginatus x x x x Redbreast sunfish L. auritus x Redear sunfish L. microlophus x x x x x x x x x x x x Spotted sunfish L. punctatus x x x x x x x x x x x x Warmouth sunfish L. gulosus x x x x x x Centrarchidae Bluespotted sunfish Enneacanthus gloriosus x x Black acara Cichlasoma bimaculatum x Cichlidae Blue tilapia Oreochromis aurea x Brook silverside Labidesthes sicculus x x Atherinopsidae Inland silverside Menidia beryllina x Mugillidae Striped mullet Mugil cephalus x x x x x x x

PAGE 52

43 Roots Snags Overhanging Brush Plants Sandbars Family Species A L D A L U D A L U D L U A L D Naked goby Gobiosoma bosc x x Gobiidae River goby Awaous banana x Achiridae Hogchoker Trinectes maculatus x x x x x x x x x Eleotridae Fat sleeper Dormitator maculatus x Centropomidae Common snook Centropomus undecimalis x x x x x x Lutjanidae Mangrove snapper Lutjanus griseus x

PAGE 53

44 LIST OF REFERENCES Anderson, N. H., J. R. Sedell, L. M. Roberst, and F. J. Triska. 1978. The role of aquatic invertebrates in processing of wood debris in coniferous forest streams. American Midland Naturalist 100:64-82. Angermeier, P. L., and J. R. Karr. 1984. Relationshipes between woody debris and fish habitat in a small warmwater stream. Transactions of the American Fisheries Society 113:716-726. Bailey, R. M., H. E. Winn, and C. L. Smith 1954. Fishes from the Escambia River, Alabama and Florida. Proceedings of the Academy of Natu ral Sciences of Philadelphia 106:109-164. Bain, M. B., and J. T. Finn. 1991. Analysis of microhabitat of fish: investigator effect and investigator bias. Rivers 2(1):57-65. Bain, M. B., J. T. Finn, and H. E. Bro oke. 1988. Streamflow regulation and fish community structure. Ecology 69:382-392. Bass, D. G., and D. T. Cox. 1985. River habi tat and fishery resources of Florida. Pages 122-188 in W. Seaman Jr., editor. Florida a quatic habitat and fishery resources. American Fisheries Society, Flor ida Chapter, Eustis, Florida. Bayley, P. B., and D. J. Austen. 2002. Ca pture efficiency of a boat electrofisher. Transactions of the American Fisheries Society 131: 435-451. Benke, A. C., R. L. Henry, III, D. M. Gillespie, and R. J. Hunter. 1985. Importance of snag habitat for animal production in south eastern streams. Fisheries 10(5):8-13. Benke, A. C., T. C. Van Arsdall, Jr., D. M. Gillespie, and F. K. Parrish. 1984. Invertebrate productivity in a subtropi cal blackwater river: the importance of habitat and life history. Ecological Monographs 54: 25-63. Benke, A. C., and J. B. Wallace. 2003. In fluence of wood on invertebrate communities in streams and rivers. Pages 149-177 in S. Gregory, K. Boyer, and A. Gurnell, editors. The ecology and management of wood in world rivers. American Fisheries Society, Bethesda, Maryland. Bonvechio, T. F., and M. S. Allen. 2005. Relations between hydr ological variables and year-class strength of sportfish in eigh t Florida waterbodie s. Hydrobiologia 532:193-207.

PAGE 54

45 Braccia, A., and D. P. Batzer. 2001. Invert ebrates associated w ith woody debris in a Southeastern U. S. forested fl oodplain wetland. Wetlands 21:18-31. Caldwell, D. K., H. T. Odum, T. R. Hellier, Jr., and F. H. Berry. 1957. Populations of spotted sunfish and Florida largemouth ba ss in a constant-temperature spring. Transactions of the American Fisheries Society 85:120-134. Carlander, K. D. 1977. Handbook of freshwater fishery biology, Volume 2. Iowa State University Press, Ames, Iowa. Carrol, A. M., P. C. Wainwright, S. H. Huskey D. C. Collar, and R. G. Turingan. 2004. Morphology predicts sucti on feeding performance in centrarchid fishes. The Journal of Experiment al Biology 207:3873-3881. Catalano, M. J., M. S. Allen, and D. J. Murie. 2006. Effects of variable flows on water chemistry gradients and fish communities at Hillsborough River, Florida. North American Journal of Fish eries Management 26:108-118. Chable, A. C. 1947. A study of the food ha bits and ecological relationships of the sunfishes of northern Florida. Masters thesis. The University of Florida, Gainesville, Florida. Crook, D. A., and A. I. Robertson. 1999. Relationships between riverine fish and woody debris: implications for lowland rivers. Marine and Freshw ater Research 50:941953. Cushman, R. M. 1985. Review of ecol ogical effects of rapidly varying flows downstream of hydroelectric facilities. North American Journal of Fisheries Management 5:330-339. Dolloff, D. A., D. G. Hankin, and G. H. R eeves. 1993. Basinwide estimation of habitat and fish populations in streams. U. S. Forest Service. General Technical Report SE-83. Asheville, North Carolina. Dolloff, C. A., and M. L. Warren, Jr. 2003. Fish relationships with large wood in small streams. Pages 179-193 in S. Gregory, K. Boyer, and A. Gurnell, editors. The ecology and management of wood in world rivers. American Fisheries Society, Bethesda, Maryland. Estevez, E. D., and M. J. Marshall. 1994. Im pact of flow variation in the Manatee River, section 2. Biological assessment of preand post-alterations. Flows and salinities. Tampa Bay National Estuary Program Tec hnial Pbulication 09-94. Prepared by Mote Marine Laboratory for Dames and M oore, Inc., Tampa Bay National Estuary Program. Evertt, R. A., and G. M. Ruiz. 1993. Coarse woody debris as a refuge from predation in aquatic communities. Oecologia 93:475-486.

PAGE 55

46 Fausch, K. D., and T. G. Northcote. 1992. Large woody debris and Salmonid habitat in a small coastal British Columbia stream. Canadian Journal of Fisheries and Aquatic Sciences 49:682-693. Flebbe, P. A., and C. A. Dolloff. 1995. Trout use of woody debris and habitat in Appalachian wilderness streams of North Carolina. North American Journal of Fisheries Management 15:579-590. Gotceitas, V., and Colgan, P. 1987. Selecti on between densities of artificial vegetation by young bluegills avoiding predation. Tran sactions of the Am erican Fisheries Society 116:40-49. Halpern, B. S., S. D. Gaines, and R. R. Warner. 2005. Habitat size, recruitment, and longevity as factors limiting population si ze in stage-structured species. The American Naturalist 165:82-94. Hellier, T. R., Jr. 1966. Fishes of the Sant a Fe River system. Bulletin of the Florida State Museum 11:1-46. Hill, J. E., and C. E. Cichra. 2005. Bi ological synopsis of five selected Florida Centrarchid fishes with an emphasis on the effects of water level fluctuations. St. Johns Water Management District. Sp ecial Publication SJ2005-SP3. Palatka, Florida. Horan, D. L., J. L. Kershner, C. P. Hawkins, and T. A. Crowl. 2000. Effects of habitat area and complexity on Colorado River cutt hroat trout density in Uinta Mountains streams. Transactions of the Am erican Fisheries Society 129:1250-1263. Hubbs, C. L., and E. R. Allen. 1943. Fishes of Silver Springs, Florida. Proceedings Florida Academy of Sciences 6:110-130. Irvine, J. R. 1985. Effects of successive fl ow perturbations on stream invertebrates. Canadian Journal of Fisheries and Aquatic Sciences 42:1922-1927. Johnson, D. L., R. A. Beaumier, and W. E. Lynch, Jr. 1988. Selection of habitat structure interstice size by blue gills and largemouth bass in ponds. Transactions of the American Fisheries Society 117:171-179. Kelly, M., A. Munson, J. Morales, and D. L eeper. 2005. Alafia River flows and levels; freshwater segment. Final Report, Sout hwest Florida Water Management District, Brooksville, Florida. Kelsch, S. W. 1994. Lotic fish-community structure following transition from severe drought to high discharge. Journa l of Freshwater Ecology. 9:331-341. Kilby, J. D. 1955. The fishes of two Gulf Coast marsh areas of Florida. Tulane Studies in Zoology 2:175-247.

PAGE 56

47 Kinsolving, A. D., and M. B. Bain. 1993. Fish assemblage recovery along a riverine disturbance gradient. Ecol ogical Applications 3:531-544. Koehn, J. D., N. A. OConnor, and P. D. Jackson. 1994. Seasonal and size-related variation in microhabitat use by a southern Victorian stream fish assemblage. Australian Journal of Freshw ater Research 45:1353-1366. Larkin, P. A. 1978. Fisheries management an essay for ecologists. Annual Review of Ecology and Systematics 9:57-73. Lobb, M. D., and D. J. Orth. 1991. Habita t use by an assemblage of fish in a large warmwater stream. Transactions of th e American Fisheries Society 120:65-78. Magnan, P., and G. J. FitzGerald. 1984. Ontogenetic changes in diel activity, food habits, and spatial distribution of juvenile and adult creek chub, Semotilus atromaculatus Environmental Biology of Fishes 11:301-307. Matthews, W. J. 1998. Patterns in freshw ater fish ecology. Chapman and Hall, New York, New York. McLane, W. M. 1955. The Fishes of the St. Johns River system. Doctoral dissertation. The University of Florida, Gainesville, Florida. McMahon, T. E., G. Gebhart, O. E. Maughan, and P. C. Nelson. 1984. Habitat suitability index models and instream flow suitability curves: warmouth. FWS/OBS-82.10.67. U. S. Fish and Wildlife Service, Washington, D.C. McMahon, T. E., and G. F. Hartman. 1989. Influence of cover complexity and current velocity on winter habitat use by juvenile coho salmon ( Oncorhynchus kisutch ). Canadian Journal of Fisheries and Aquatic Sciences 46:1551-1557. Mittelbach, G. G. 1984. Predation a nd resource partitioning in two sunfishes (Centrarchidae). Ecology 65:499-513. Moore, K. M. S., and S. V. Gregory. 1988. Summer habitat uti lization and ecology of cutthroat trout fry ( Salmo clarki ) in Cascade Mountain str eams. Canadian Journal of Fisheries and Aquatic Sciences 45:1921-1930. Nickelson, T. E., J. D. Rodgers, S. L. Johnson, and M. F. Solazzi. 1992. Seasonal changes in habitat use juvenile coho salmon (Oncorhyncus kisutch) in Oregon coastal streams. Canadian Journal of Fisheries and Aquatic Sciences 49:783-789. Peters, J. C. 1982. Effects of river and streamflow alteration on fishery resources. Fisheries 7(2):20-22. Power, G., R. S. Brown, and J. G. Imhof. 1999. Groundwater and fish insights from northern North America. H ydrological Processes 13:401-422.

PAGE 57

48 Raibley, P. T., T. M. OHara, K. S. Irons, K. D. Blodgett, and R. E. Sparks. 1997. Largemouth bass size distributions unde r varying annual hydrological regimes in the Illinois River. Transactions of th e American Fisheries Society 126:850-856. Reynolds, J. B. 1996. Electrofishing. Pages 221-253 in B. R. Murphy and D. W. Willis, editors. Fisheries Techniques, 2nd Edition. American Fisheries Society, Bethesda, Maryland. Rogers, M. W., M. S. Allen, and M. D. Jone s. 2005. Relationships between river surface levels and fish assemblages in the Ocklaw aha River, Florida. River Research and Applications 21:501-511. Rosenberger, A., and P. L. Angermeier. 2003. Ontogenetic shifts in habitat use by the endangered Roanoke logperch ( Percina rex ). Freshwater Biology 48:1563-1577. Rosenfeld, J. 2003. Assessing the habitat re quirements of stream fishes: an overview and evaluation of different approaches. Transactions of the American Fisheries Society 132:953-968. Rozas, L. P., and W. E. Odum. 1988. O ccupation of submerged aquatic vegetation by fishes: testing the roles of food and refuge. Oecologia 77:101-106. SAS Institute. 2002. SAS Users Guide: Statistics, Version 8, 4th edition. SAS Institute, Cary, North Carolina. Savino, J. F., and R. A. Stein. 1982. Pr edator-prey interaction between largemouth bass and bluegills as influenced by simulated s ubmersed vegetation. Transactions of the American Fisheries Society 111:255-266. Scheaffer, R. L., W. Mendenhall, and L. Ott. 1990. Elementary survey sampling, 4th edition. PWS-KENT, Boston, Massachusetts. Schlosser, I. J. 1985. Flow regime, juvenile abundance, and the a ssemblage structure of stream fishes. Ecology 66:1484-1490. Shirvell, C. S. 1990. Role of inst eam rootwads as juvenile coho salmon ( Oncorhyncus kisutch ) and steelhead trout ( O. mykiss ) cover habitat under va rying steamflows. Canadian Journal of Fisheries and Aquatic Sciences 47:852-861. Simonson, T. D., J. Lyons, and P. D. Kanehl. 1994. Quantifying fish habitat in streams: transect spacing, sample size, and a propos ed framework. North American Journal of Fisheries Management 14:607-615. Sklar, F. H., and J. A. Browder. 1998. Coastal environmental impacts brought about by alterations to freshwater flow in the Gu lf of Mexico. Envi ronmental Management 22:547-562.

PAGE 58

49 Smock, L. A., E. Gilinsky, and D. L. Stoneburner. 1985. Macroinvertebrate production in a southeastern United States bl ackwater stream. Ecology 66: 1491-1503. Steigerwalt, N. M. 2005. Environmenta l factors affecting aq uatic invertebrate community structure on snags in the Ichetucknee River, Florida. Masters thesis. The University of Florida, Gainesville, Florida. Todd, B. L., and C. F. Rabeni. 1989. Movement and habitat use by stream-dwelling smallmouth bass. Transactions of the American Fisheries Society 118:229-242. Travnichek, V. H., M. B. Bain, and M. J. M aceina. 1995. Recovery of a warmwater fish assemblage after the initiation of a mi nimum-flow release downstream from a hydroelectric dam. Transactions of th e American Fisheries Society 124:836-844. Tyus, H. M. 1990. Effects of altered st reamflows on fishery re sources. Fisheries 15(3):18-20. Van Horne, B. 1983. Density as a misleadi ng indicator of habitat quality. Journal of Wildlife Management 47:893-901. VanderKooy, K. E., C. F. Rakocinski, and R. W. Heard. 2000. Trophic relationships of three sunfishes ( Lepomis spp.) in an estuarine ba you. Estuaries 23:621-632. Warren, G. L., D. A. Holt, C. Cichra, and D. VanGenecten. 2000. Fish and aquatic invertebrate communities of the Wekiva and Little Wekiva Rivers: a baseline evaluation in the context of Floridas mini mum flows and levels statues. St. Johns River Water Management District Speci al Publication SJ2000-SP4, Palatka, Florida. Werner, E. E., and J. F. Gilliam. 1984. The ontogenetic niche and species interactions in size-structured populations Annual Reviews in Ecology and Systematics 15:393425. Werner, E. E., J. F. Gilliam, D. J. Hall, a nd G. G. Mittelbach. 1983. An experimental test of the effects of pr edation risk on habitat us e in fish. Ecology 64:1540-1548. Weyers, R. S., C. A. Jennings, and M. C. Freeman. 2003. Effects of pulsed, highvelocity water flow on larval robust redhor se and v-lip redhorse. Transactions of the American Fisheries Society 132:84-91. Wheeler, A. P., and M. S. Allen. 2003. Ha bitat and diet partiti oning between shoal bass and largemouth bass in the Chipola River, Florida. Transactions of the American Fisheries Society 132:438-449.

PAGE 59

50 BIOGRAPHICAL SKETCH Andrew (Drew) Carl Dutterer was born on October 17, 1979, in Athens, Georgia. In 1984 he and his family relocated to the No rth Carolina foothills, just outside of the small town of Dallas. Drew enrolled at North Carolina State University following graduation from high school in 1998. While attending N.C. State, Drew received a bachelors degree in environmental sciences with an emphasis in ecology. In 2004, Drew enrolled at the University of Florida to pursue a Master of Science degree, while conducting research through the Department of Fisheries and Aquatic Sciences. He completed his graduate studies with the Univ ersity of Florida in the summer of 2006. Drew is a washed-up artist, closet musician incompetent outboard mechanic, swell cook, and fair biologist. First and foremost, howev er, he is an avid outdoorsman and for most of his life fishing has been a passion, pres enting that insatiable itch to scratch.


Permanent Link: http://ufdc.ufl.edu/UFE0016066/00001

Material Information

Title: Microhabitat Relationships for Spotted Sunfish at the Anclote, Little Manatee, and Manatee Rivers, Florida
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0016066:00001

Permanent Link: http://ufdc.ufl.edu/UFE0016066/00001

Material Information

Title: Microhabitat Relationships for Spotted Sunfish at the Anclote, Little Manatee, and Manatee Rivers, Florida
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0016066:00001


This item has the following downloads:


Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
    Table of Contents
        Page v
    List of Tables
        Page vi
    List of Figures
        Page vii
    Abstract
        Page viii
        Page ix
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Methods
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Results
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
    Discussion
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Appendix: Sampling locations and community summary
        Page 40
        Page 41
        Page 42
        Page 43
    References
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    Biographical sketch
        Page 50
Full Text












HABITAT RELATIONSHIPS FOR SPOTTED SUNFISH AT THE ANCLOTE,
LITTLE MANATEE, AND MANATEE RIVERS, FLORIDA













By

ANDREW C. DUTTERER


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


2006

































Copyright 2006

by

Andrew C. Dutterer


































This thesis is dedicated to the preservation and sustainable management of Florida's
aquatic resources.















ACKNOWLEDGMENTS

I thank my committee, Drs. Mike Allen and Tom Frazer, and Mr. Eric Nagid, for

guidance throughout the preparation of this thesis.

I thank Christian Barrientos, Jason Bennett, Greg Binion, Matt Catalano, Steve

Crawford, Jason Dotson, Kevin Johnson, Galen Kaufman, Vaughn Maceina, Vince

Politano, Mark Rogers, and Nick Trippel for assistance in data collection.

I thank Mark and Laura Stukey (Ray's Canoes), Mr. and Mrs. Don Bislich, and Mr.

James Blincoe (Little Manatee River State Park) for their willingness to provide me

access to private or limited-access boat ramp facilities.

I thank Dr. Mary Christman for her advice and suggestions concerning the

statistical analyses of portions of my research.

I thank the Southwest Florida Water Management District for providing funding for

this research.

Most of all, I thank my parents (Carl and Mary Ann) for their continued support

throughout all of my endeavors. I could not have asked for a better family.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ............. ................... .. .......... .................................... vi

LIST OF FIGURES ............................. .. .......... .................................... vii

ABSTRACT ................................................... ................. viii

CHAPTER

1 IN TR O D U C T IO N ........ .. ......................................... ..........................................1.

B background ................................................................................................... ...............1
O bjectiv e s ........................................................................ ................................. . .2
Study L locations ............................................................................................................3

2 M E T H O D S ....................................................................... ................................. . 5

A approach and Sam pling U nits ................................................................................5
Spotted Sunfish Sam pling ..........................................................................................6
H habitat M easurem ent .................................................................................................8
Habitat-Specific Community Assessment .............................................. .................. 11
Statistical A analyses ............................................................................................... 12

3 R E S U L T S .......................................................................................... ..................... 14

Spotted Sunfish H habitat Utilization ............................................... ..........................14
Effects of Altered Stage/Flow on Habitat Availability............................................17
Habitat-Specific Fish Community Analysis ................. ...................................18

4 D ISC U SSIO N ............................................................................... ...................... 29

APPENDIX

SAMPLING LOCATIONS AND COMMUNITY SUMMARY...................................40

L IST O F R E F E R E N C E S ................................................................................................... 44

BIO GRAPH ICAL SK ETCH ..........................................................................................50


v















LIST OF TABLES


Table page

1 Mean and standard deviation (SD) of habitat parameters for utilized and
available habitat intervals at Anclote River and Manatee River downstream and
u p stream site s. ......................................................................................................... 2 1

2 Mean and standard deviation (SD) of habitat parameters for utilized and
available habitat intervals per season and year for Little Manatee River. ..............22

3 Mean and standard deviation (SD) of habitat parameters for adult, juvenile, and
available habitat intervals at Anclote River and Manatee River downstream and
u p stream site s. .......................................................................................................... 2 3

4 Mean and standard deviation (SD) of habitat parameters for adult, juvenile, and
available habitat intervals per season and year at Little Manatee River ............... 24

5 Latitude and longitude coordinates for spotted sunfish sampling reaches at
Anclote, Little Manatee, and Manatee Rivers, Florida. ....................................40

6 Habitat-specific list of fish species collected from the Anclote (A), Little
Manatee (L), Manatee upstream (U) and Mantee downstream (D) rivers ............41















LIST OF FIGURES


Figure page

1 Locations of the Anclote, Little Manatee, and Manatee Rivers in relation to
Tam pa Bay along the Gulf Coast of Florida ........................................ ...............4...

2 Hydrographs representing average daily stage (meters, mean sea level) data for
the Anclote, Little Manatee, and Manatee River downstream sites during the
tw o-year study period. .............. .............. ............................................ 25

3 Proportion of total habitat intervals per river with habitat remaining inundated (y
axis) with incremental decline in average river stage (m, x axis). ........................26

4 Box plots of fish species richness (y axis) for each system. ..............................27

5 Box plots of fish diversity (y axis) for each system. .........................................28















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Master of Science

HABITAT RELATIONSHIPS FOR SPOTTED SUNFISH AT THE ANCLOTE,
LITTLE MANATEE, AND MANATEE RIVERS, FLORIDA

By

Andrew C. Dutterer

December 2006

Chair: Micheal S. Allen
Major Department: Fisheries and Aquatic Sciences

Establishing river minimum flow and level (MFL) regulations to maintain

ecosystem health is a top priority for Florida's management agencies due to expanding

human population size and water demand. The spotted sunfish Lepomispunctatus is

sensitive to changes in river water levels and could potentially serve as an indicator for

ecosystem health, within the context of water level fluctuation and management.

I measured characteristics of habitat (i.e., current velocity, depth, substrate, cover

abundance) utilized by spotted sunfish and compared them to overall available habitat

within the stream margin environment to identify patterns of habitat selection at three

southwestern Florida Rivers (Anclote, Little Manatee, and Manatee). Multivariate

Analysis of Variance (MANOVA) was used to test whether habitat metrics collectively

differed between available and utilized habitats. I assessed how fluctuations in river

stage and flow could influence spotted sunfish habitat availability. I also assessed fish

community richness and diversity patterns among the predominant habitat types within









each system. All sampling occurred from November 2004 to March 2006 during fall and

spring seasons.

Overall, spotted sunfish tended to select habitat having greater structural

complexity than the average available habitat. In many instances, spotted sunfish

appeared to select large and fine woody debris habitats. However, I collected spotted

sunfish from a variety of habitat types through the study, indicating that the species was

somewhat general in its habitat associations. I found few significant differences in

habitat measures between juvenile and adult fish, suggesting that habitat associations

were similar between the life stages.

My simulations indicated that 0.3-meter reductions in average daily stage could

reduce habitat availability for spotted sunfish by up to 20% across systems. Overall,

habitats utilized by spotted sunfish were more resilient to stage declines due to fish

utilization of areas with deeper depths and more complex habitat than the average

conditions. I found that fish richness tended to vary among habitat types at all systems,

and relatively complex habitat such as woody debris and aquatic plants frequently

exhibited higher fish richness than less complex habitats such as sandbars.

I conclude that the inundation of complex habitat types is likely important for

spotted sunfish, and even minor changes in the average daily stage during fall and spring

seasons could substantially reduce overall availability of these habitat types. Habitats

utilized by spotted sunfish also exhibited high total fish richness, suggesting that

protection of complex habitats will benefit the fish communities of southwest Florida

Rivers. Results of this study can serve to inform resource managers responsible for

setting MFL regulations to aid in the protection of habitat for freshwater fishes.














CHAPTER 1
INTRODUCTION

Background

Water allocation and the ability to reach a balance between the needs of society and

the natural environment are growing concerns among water resource managers and

stakeholders, especially within the state of Florida. One critical step in the protection of

Florida's water resources is the implementation of Minimum Flows and Levels (MFL)

for priority water bodies (373.042, Florida Statutes). The MFL policies facilitate the

regulation of surface water diversion and ground water withdrawal such that variation in

streamflow and surface water levels can sustain the ecological integrity of each water

body (373.042, Florida Statutes).

Fisheries managers have noted that maintaining high quality river fisheries in light

of increases in human population and land development would be a major challenge

(Peters 1982; Bass and Cox 1985; Tyus 1990). Anthropogenic modifications in

streamflow and resulting habitat alteration can strongly influence the abundance and

composition of aquatic fauna (Cushman 1985; Irvine 1985; Schlosser 1985; Bain et al.

1988; Kinsolving and Bain 1993; Travnichek et al. 1995; Power et al. 1999). Stream fish

community metrics and population dynamics have been correlated with water level and

streamflow changes (Kelsch 1994; Raibley et al. 1997; Weyers et al. 2003). Bonvechio

and Allen (2005) linked year-class strength of several Centrarchid species to seasonal

variation in flow/stage for four Florida Rivers.









The spotted sunfish Lepomispunctatus, a member of the Centrarchidae family, is

one of the most abundant species in native stream fish assemblages of Florida rivers

(Hubbs and Allen 1943; Bailey et al. 1954; McLane 1955), and has been shown to exhibit

population responses to fluctuating flow and stage (Rogers et al. 2005). Rogers et al.

(2005) found that spotted sunfish abundance was low following persistently low flow and

stage conditions during the year prior to sampling at the Ocklawaha River, Florida. They

believed that spotted sunfish could serve as an indicator species for MFL regulation due

to the apparent population responses to changing streamflow and stage.

However, habitat associations of the spotted sunfish remain largely uninvestigated.

Studies have shown that structurally complex cover, such as woody debris (Anderson et

al. 1978; Angermeier and Karr 1984; Benke et al. 1985; Lobb and Orth 1991) and aquatic

macrophytes (Rozas and Odum 1988; VanderKooy et al. 2000) provide important forage

and refuge locations for stream fish communities. Spotted sunfish have been observed to

utilize dense vegetation and fallen trees along stream margins (McLane 1955), and diet

analyses indicate that spotted sunfish feed on invertebrates associated with aquatic

vegetation (VanderKooy et al. 2000) and submerged snags (Benke et at. 1985). The

inundation and availability of these habitat types, often characteristic of stream margins

and important to stream fish communities, can be strongly influenced by fluctuations in

flow and stage (Bain et al. 1988).

Objectives

My objectives were to

1) identify habitat associations for juvenile and adult spotted sunfish relative to
available habitat at the Anclote, Little Manatee, and Manatee Rivers,

2) predict how changes in river stage/flow for each system would influence habitat
availability for spotted sunfish, and









3) identify habitat-specific fish community composition for each river system.

Findings will help guide the establishment of MFL regulations for each river, so habitats

for spotted sunfish and the broader fish community can be protected.

Study Locations

This study included the Anclote, Little Manatee, and Manatee Rivers of the central

Gulf Coast of Florida (Figure 1). The Anclote River flows generally east to west and

discharges into the Gulf of Mexico between the towns of Holiday and Tarpon Springs,

Florida. The Little Manatee River discharges into Hillsborough Bay, the westernmost

portion of Tampa Bay, whereas the Manatee River discharges into the Gulf of Mexico at

the southern region of Tampa Bay. Similar to the Anclote River, the Manatee and Little

Manatee Rivers also flow from east to west, with all rivers having relatively short

distances (i.e., 20-40 km) between headwaters and river mouths. All rivers exhibit a

sinuous, meandering channel typical of low gradient streams (Figure 1).



















































Figure 1. Locations of the Anclote, Little Manatee, and Manatee Rivers in relation to
Tampa Bay along the Gulf Coast of Florida. Approximate locations of sample
sites in each river are indicated by red arrows. Specific latitude and longitude
coordinates of sampling site boundaries are provided in Table 5 of the
Appendix.














CHAPTER 2
METHODS

Approach and Sampling Units

Habitat selection has been defined many ways in the literature, and it was important

in this study to clearly define "habitat selection" as used here. Rosenfeld (2003, p. 954)

advocated that

habitatt selection (i.e., differential occupancy) occurs when an organism avoids a
particular habitat (negative selection) or uses a habitat in greater proportion than its
availability in the environment (positive selection). Habitat selection can be
demonstrated if fish occur at higher densities in particular habitats, or if fish occur
at higher frequencies in particular microhabitats to relative frequency of that
microhabitat in the environment.

My use of the term "habitat selection" refers to the differential utilization of habitat

relative to its availability within the environment. Thus, the overall approach of my study

was to evaluate the habitat selection of spotted sunfish by characterizing the overall

available habitat conditions within study locations and then to compare these data to

habitat characteristics from which spotted sunfish were collected.

During pilot sampling at each river, I observed available habitat types (e.g., woody

debris, overhanging root wads, and aquatic macrophytes) interspersed throughout each

river system. As the mix of habitat types typically occurs across a relatively small

longitudinal stream distance (< 500 m), cluster sampling was determined to be an

appropriate sampling strategy (Schaeffer et al. 1990). Cluster sampling entails selecting

replicate sample areas that include all available habitat types, so that variation among

sample areas (i.e., clusters) is relatively small, but variation among systems (i.e., rivers) is









relatively large. Within each river system, I utilized longitudinal sections of river

channel, referred to as a river reach, as my sampling replicate. River reaches were 500 m

in length at each river, because this size included all available habitat types present in

each system. Three reaches were selected for sampling on the Anclote and Manatee

Rivers, whereas at the Little Manatee River, I selected five reaches for sampling. During

pilot sampling on the Little Manatee River I encountered two distinct 'zones' of channel

morphology. Within the upper zone of the sampling region, I found that the channel

width typically ranged between 15 20 m. The downstream zone of the sampling region

had a wider channel, typically between 30 50 m, and it tended to support a greater

abundance of rooted aquatic vegetation along banks, presumably due to a lesser degree of

shading by the adjacent riparian overstory. Therefore, for Little Manatee River I selected

three reaches within the upper zone and two reaches within the downstream zone of the

sampling region to more fully characterize the habitat types available within this system.

I sampled spotted sunfish and stream fish communities at two geographically

disparate locations on Manatee River. During the first year of the study, I sampled within

reaches located upstream of Lake Manatee, whereas sampling during the second year was

conducted below the Lake Manatee dam. The appendix (Table 5) provides the latitude

and longitude coordinates of all sampling reaches. River stage and discharge (when

available) for the study period were obtained for each system from T. Carson, U. S.

Geological Survey.

Spotted Sunfish Sampling

Spotted sunfish were sampled between November 2004 and March 2006, with an

emphasis placed on fall and spring sampling. Typically, spring and fall seasons along the

central Gulf Coast of Florida have relatively low rainfall compared to summer. Thus,









streamflows within this region are likely to be near base flow conditions during spring

and fall. My sampling during spring (March-May) and fall (November-December) was

designed to evaluate habitat associations for spotted sunfish during relatively stable and

low flow conditions.

I sampled the Anclote and Little Manatee Rivers once each during fall and spring

seasons from November 2004 to March 2006. In total, there were two fall samples and

two spring samples for each of these rivers. The Manatee River upstream samples were

collected during fall 2004 and spring 2005, whereas, the Manatee River downstream

samples were collected during fall 2005 and spring 2006.

Spotted sunfish were collected using boat electrofishing gear that consisted of a

4.6-m aluminum jon boat powered by a 50-horsepower outboard motor with bow

mounted anode probes. I used electrical power output of 5-8 Amps pulsed DC current

regulated through a model VI-A Smith-Root pulsator. Power was supplied by a Honda

5000-watt AC generator.

My method of operating the electrofishing boat utilized two field personnel, one to

operate the boat and pulsator located near the stem, and a second, located on the bow, to

identify, collect, and measure spotted sunfish. For each reach, there were essentially two

electrofishing transects, one conducted along each bank for the entire 500-m. Field

personnel operated the electrofishing boat along each bank at a slow, but consistent speed

to ensure that all portions of each bank regardless of available habitat received equal

effort. All electrofishing samples were conducted during daylight hours, approximately

between 7:00 am and 5:00 pm.









Following visual identification of a spotted sunfish, the location of each individual

was marked, as precisely as possible, with either a bright orange flag, when proximity to

shore or water depth permitted, or a bright orange buoy tethered to an anchor. I made

efforts to locate spotted sunfish intervals at the point where an individual was first seen

within the electromagnetic field. If I suspected that substantial electrotaxis or drifting

had occurred by an individual, it was not used for habitat data collection. I measured

each spotted sunfish to nearest mm total length and classified individuals as adult (> 60

mm TL) or juvenile (< 60 mm TL) (Caldwell et al. 1957; Carlander 1977). In the case

that two or more individuals were located within a 0.5-m radius of one another, I marked

the multiple locations as at the most central point.

Habitat Measurement

For this study, a habitat interval refers to a cylindrical volume of water horizontally

defined by a 1 meter radius centered on a marked spotted sunfish location, spanning the

vertical distance from water surface to substrate. My goal was to quantitatively describe

the habitat characteristics present within each interval. Habitat measurements included

depth, distance from bank, predominant substrate type, current velocity at 60% depth,

large woody debris size category and abundance, aquatic macrophyte type and density,

and cover penetration to the substrate (see below for explanation of terms). Depth,

distance from bank, and cover penetration were measured to the nearest decimeter.

Current velocity was measured with a Model 2000 Marsh-McBurney Flowmate

flowmeter. I used a Woody Debris Index (WDI), very similar to that outlined by Dolloff

et al. (1993), to quantify aggregations of large woody debris within habitat intervals.

Pieces of large woody debris were categorized by cross-sectional diameter and counted.

Large woody debris size categories were: (I) 5-10 cm in diameter, and (II) greater than 10









cm in diameter. A single WDI score was calculated for each interval using the following

equation

WDI = WDI + 2(WD2) (1)
where WDI = count of woody debris size (I), and WD2 = count of woody debris size (II).

Pieces of woody debris having a cross-sectional diameter less than 5 cm were categorized

as fine woody debris (FWD), and abundance of FWD was estimated visually as the

percentage of the interval volume occupied (PVO). The category FWD included

overhanging terrestrial brush, root wads, and other small diameter woody structure.

Aquatic macrophyte abundance was also estimated visually as percentage of the interval

volume inhabited (PVI).

To form a less specific descriptor of habitat cover complexity, I formulated a

Habitat Complexity Index (HCI). The HCI combines proportions of large woody debris

counts, FWD abundance, and aquatic macrophyte abundance for each interval. I

standardized the habitat metrics as a proportion of the maximum value for each parameter

across all rivers and sampling dates. The standardized metrics were combined to create

the HCI for each interval as

HCJ WDI. WD2q (PlantPVI9 (FWDPVO (2)
10 8 90 80
where WDI = count of woody debris size (I), WD2 = count of woody debris size (II),

PlantPVI = percent of interval inhabited by aquatic macrophytes, and FWDPVO =

percent of interval occupied by fine woody debris. The denominators in equation 2

represented the maximum values across all systems and intervals, for standardization to

proportions.









Cover penetration (P) was measured as the percentage of interval depth occupied

by all combined habitat metrics in relation to the stream surface. For example, plants and

woody debris that reached to a depth of 1 m within a 2-m deep interval were assigned a

penetration value of 50%. Penetration values were used to estimate loss of spotted

sunfish habitat with decline in river stage (below).

Available habitat was measured along equally spaced transects perpendicular to

streamflow within each stream reach, similar to methods proposed by Simonson et al.

(1994) and implemented by Wheeler and Allen (2003). For each habitat sampling event,

the location of the first transect was located downstream from the upstream boundary of a

stream reach at a randomly generated distance between 0 and 100 m. Thereafter, each

transect was progressively located 100 m downstream from the previous transect until a

total of five habitat availability transects were completed for each sampling reach. Two

habitat availability intervals, centered one meter from each stream bank, were located

along each transect line, and habitat parameters were measured in the same manner as for

intervals utilized by spotted sunfish. Thus, available and utilized habitats were measured

at the same spatial scale.

I used the habitat characteristics sampled from each river to predict how reductions

in average river stage would influence habitat availability for spotted sunfish. I surmised

that habitat availability and resiliency to changing water levels could be described by

HA = [(D P)- L] HCI (3)

where HA is the habitat availability for the interval, D is the water depth in m, L is a

simulated incremental decline in average stage in meters, HCI is the habitat complexity

index, and P is the cover penetration. I simulated values of L ranging from 0 to 2 meters

with 0.1-m increments. For each incremental decline in L, I estimated the proportion of









habitat intervals P(HA) where HA would decline to zero. Thus, the value 1-P(HA)

depicted the proportion of habitat intervals where some portion of cover remained

inundated following each incremental 0.1-m decline in river stage (L). I obtained values

of 1-P(HA) separately for utilized and available habitat intervals for each system, which

assessed how habitats used by spotted sunfish varied from the random habitat intervals

regarding potential habitat loss.

Habitat-Specific Community Assessment

To address my third objective, I sampled fish communities at each river. I

conducted habitat-specific community electrofishing at the Anclote and Little Manatee

Rivers during April and December 2005. For the Manatee River, community sampling

was conducted once at the upstream site during April 2005, and once at the downstream

site during December 2005. My goals were to document species richness and diversity

and identify potential differences in these community metrics with respect to differences

in predominant habitat types, similar to Lobb and Orth (1991). To formulate diversity

values, I used Shannon-Wiener's index of biological diversity:


H'= (p)- (log2 P)
z=l
where H'= Shannon-Wiener index of biological diversity, s = number of species, and

p, = proportion of total sample belonging to ith species. I used the same areas within

each river for community sampling as with spotted sunfish sampling. The same boat

mounted electrofishing gear was used for community sampling as for spotted sunfish

sampling. I used 300-second electrofishing transects as sample replicates for each habitat

type. During each transect, the electrofishing boat was maneuvered such that the

electromagnetic field was maintained only near a single habitat type. I then progressively









moved the boat from one patch of selected habitat to another of the same type, and this

technique was continued throughout the duration of each transect. A minimum of four

transects were collected for each habitat type at each river and community sampling

event (i.e., season). All fish collected were identified to species, tallied, and measured to

the nearest millimeter total length on site. Any unidentifiable individuals were preserved

on ice and later keyed to species in the laboratory.

Statistical Analyses

Habitat variables measured at each interval were highly non-normal due to the

proportional and categorical scales of the data (e.g., PVI, WDI). I transformed all habitat

values to the ranks in order to construct non-parametric multivariate analyses of variance

(MANOVA). The MANOVA's tested the null hypothesis that the mean ranked habitat

variables (flow, depth, WDI, FWD, PlantPVI) collectively did not differ between utilized

and available habitat intervals. The MANOVAs were constructed separately for each

river with the following fixed effects: interval type (available vs. utilized), season, year,

and the interactions of these values. The effect reach(river) was used as a block effect to

account for any variation explained among reaches, which was expected to be low due to

the cluster sampling design. The MANOVA analyses were repeated for three levels of

interval type (adult, juvenile, and available) to assess differences in habitat utilization

between adult and juvenile life stages. I analyzed data from each river separately for a

total of eight MANOVA tests (four total sampling areas in the Anclote, Little Manatee,

and Manatee upstream and downstream, two MANOVA each). For the Manatee River

sections, the year effect was not possible to evaluate because I sampled each section

(upstream and downstream) in only one fall and spring, resulting in interval type and

season as fixed effects. When significant effects were detected with the MANOVAs, the









least squares means procedure (SAS 2002) was used to identify the effects that

contributed to the differences.

I used three-way analysis of variance (ANOVA) to test for differences in mean HCI

scores between utilized and available habitat intervals at Anclote and Little Manatee

Rivers. Fixed effects were interval type, year, and season as described above. I used a

two-way ANOVA to test for differences in mean HCI scores at Manatee River upstream

and downstream locations with interval type and season serving as the fixed effects.

Because I sampled Manatee River upstream and downstream reaches each during a single

year, there was no fixed effect of year.

To test for differences in mean species richness and diversity among predominant

habitat types at Anclote and Little Manatee Rivers, I use two-way ANOVA. Fixed

effects included habitat type and season. I used one-way ANOVA to test for differences

in mean species richness and diversity among habitat types at both Manatee River

sampling locations. Community samples were conducted once at each location on the

Manatee River. Thus, habitat type was the only fixed effect.














CHAPTER 3
RESULTS

Spotted Sunfish Habitat Utilization

I collected habitat parameter measurements at a total of 470 available and 915

utilized habitat intervals across all sampling locations. At Anclote River, I characterized

120 available intervals and 292 utilized intervals. With regard to the utilized intervals at

Anclote River, 178 were occupied adults and 114 by juveniles. At Little Manatee River,

I characterized 210 available intervals and 473 utilized (329 adult and 144 juvenile)

habitat intervals. At the Manatee River downstream site, I characterized 60 available and

72 utilized (60 adult and 12 juvenile) habitat intervals, and at the Manatee River upstream

site, I characterized 80 available and 78 utilized (52 adult and 26 juvenile) habitat

intervals.

The MANOVA analyses testing for differences in collective habitat variables

between utilized and available intervals were significant for all rivers, but some river-

specific differences occurred. For the Anclote and Manatee downstream site, there were

no significant interactions (all P > 0.25) but the interval effect was significant indicating

that habitat variables where spotted sunfish were collected differed from the available

interval habitat variables (Table 1). Spotted sunfish were collected from areas with

higher WDI and FWD than the available intervals at both systems (Table 1). Water depth

was greater for utilized than available intervals at the Anclote River (Table 1). The

MANOVA for habitat data from the Manatee River upstream site indicated a significant

two-way interaction (P = 0.034) between interval types (available vs. utilized) and









season. This interaction was due to significant differences in utilized habitat WDIs

between seasons and was of little importance for comparisons between interval types.

For the Little Manatee River, I found a significant three-way interaction between

interval type (utilized vs. available), season (spring and fall), and year (first and second)

(P < 0.0001). This interaction occurred because significant relationships among interval

types were not consistent for either season, between years (Table 2). For example,

utilized versus available habitat variables differed for depth, WDI, and FWD in the spring

of 2006, whereas only depth differed between interval types in fall 2004 (Table 2). All

other statistical tests did not indicate significant interactions between interval types and

season or year (all P > 0.379).

Generally, adult and juvenile size-classes of spotted sunfish displayed similar

habitat use patterns, and both size classes were associated with structurally complex

habitat. For the Anclote River and the Manatee River downstream site, the MANOVA

exhibited a significant interval effect (both P < 0.0001) without any significant

interactions (all P > 0.109). Both adult and juvenile spotted sunfish utilized areas with

high WDI and FWD relative to available intervals. However, intervals occupied by

juveniles had significantly greater plant densities than intervals occupied by adults or

available intervals (both P < 0.057) at the Manatee River downstream site (Table 3). No

differences were detected between life stages at the Manatee upstream site (Table 3).

Similar to the combined life stage analysis, I found a three-way interaction among

interval type (juvenile, adult, available), season, and year at the Little Manatee River

(Table 4) (P < 0.0001). This interaction occurred because juvenile spotted sunfish

occurred in habitats that were intermediate between adult and available intervals, and









these effects were most apparent in spring 2006 (Table 4). For example, adults were

collected from intervals with deeper depths and higher WDI and FWD than the available

intervals in spring 2006, but habitat where juveniles occurred during directed sampling

was intermediate to the these values for the spring 2006. The depth variable also differed

between adult and available habitat intervals during fall 2004, with depth being

intermediate for habitats occupied by juveniles (Table 4). Thus, the relationships of

utilized and available habitat for juveniles and adults generally mirrored the relationships

I observed when size-classes were aggregated.

My use of the HCI score indicated that spotted sunfish were usually associated with

physical habitat having greater structural complexity relative to that of the representative

available habitat. The mean HCI scores for utilized versus available habitat were

significantly greater (P < 0.0001) at the Anclote (0.47 versus 0.27), and the Manatee

River downstream site (0.65 versus 0.20). The Manatee River upstream site showed an

opposite relationship with HCI scores being higher for available (0.48) versus utilized

(0.34) intervals (P < 0.0001). Similar to the MANOVA for collective habitat variables,

the three-way ANOVA for HCI scores showed a significant three-way interaction at the

Little Manatee River (P < 0.0001), where HCI scores were higher for utilized than

available intervals in the fall 2004 (0.47 versus 0.33) and spring 2006 (0.44 versus 0.26,

both P < 0.045). Thus, the use of HCI showed the same relationships as the MANOVA

using all habitat variables, where spotted sunfish utilized locations with higher habitat

complexity than the more general available conditions within most systems. The

Manatee River upstream site differed from the other systems and showed some opposite









patterns, but this likely occurred because of the more homogenous nature of the habitat

conditions at this site.

Effects of Altered Stage/Flow on Habitat Availability

My study rivers are located in Southwest Florida, where rainfall patterns consist of

a summer wet season with a relatively dry spring, winter, and fall (Kelly et al. 2005). My

study design sampled these rivers in spring and fall during periods when river flow and

stage are relatively low. Water levels during our sampling were similar between years

(Figure 2) and representative of the average, relatively low flow conditions expected

during these seasons. However, all of my study reaches except the Manatee River

upstream were tidally influenced and exhibited stage variation of about 0.3 meters

throughout the day. Flow direction varied from downstream to occasionally upstream

with outgoing and incoming tides. Nevertheless, all of the study sites had low salinity (<

5 ppt) throughout this study as indicated by my collection of obligate freshwater fishes on

all sampling events and the ability to use a freshwater electrofishing arrangement as the

sampling gear.

Simulations of HA indicated that average stage declines of 0.3 m could result in 0

to 20% habitat loss for spotted sunfish across systems (Figure 3). The Southwest Florida

Water Management District has used a criterion of 15% habitat loss as significant for

coastal rivers (Kelly et al. 2005), and my simulations indicated that this degree of habitat

loss would occur with average stage declines of 0.3 m or less in three of four systems.

The largest decline in available habitat occurred at the Manatee River downstream site

and the smallest at the Manatee River upstream site (Figure 3). The Anclote and Little

Manatee Rivers exhibited about 20% losses in habitat availability with a 0.3 m reduction

in average stage, and 40-50% habitat loss with a 0.6 m reduction. The Manatee River









upstream site was characterized by relatively steep banks and abundant aquatic plants

(primarily Maidencane Panicum hemitomon) extending out to 1-2 m water depths, which

made habitat loss less susceptible to changes in water levels. For the other three systems,

a 0.3 m decline in average stage was predicted to reduce available habitat by 15-20%

(Figure 3).

Spotted sunfish utilized habitat intervals that were more resilient to changes in river

stage than the average condition at all rivers except the Manatee River upstream site.

Utilized habitat intervals exhibited more gradual declines in habitat availability with

incremental declines in average stage at the Anclote, Little Manatee, and Manatee River

downstream site (Figure 3). This occurred because spotted sunfish utilized intervals that

were deeper and had more complex habitat than the available habitat intervals at each

system. The Manatee River upstream site exhibited little difference in habitat availability

between utilized and available intervals, and slightly lower habitat loss for available

intervals at a 0.6 m average stage decline (Figure 3). Because this site was located above

the impoundment, the habitat conditions (e.g., flow, stage, HCI) were likely influenced

by the dam, resulting in habitat relationships that were not similar to our other study sites

or other southwest Florida streams. All other stream sites in this study exhibited

relatively rapid habitat loss with declines in average stage.

Habitat-Specific Fish Community Analysis

Over the course of this study, I collected 23 fish species at the Anclote River, 26 at

the Little Manatee River, 12 at the Manatee River upstream and 21 species at the

Manatee River downstream. Collectively, there were 26 species collected from the

Manatee River system. Thus, overall fish species richness was similar among river

systems and ranged from 23 to 26. Individual fish species and the habitats from which









they were collected within each river are shown in the Appendix (Table 6). The family

Centrarchidae was the most common family with eight species (Appendix, Table 6). As

expected for these coastal systems, fish taxa represented a range of obligate freshwater

(e.g., Centrarchidae) to estuarine species (e.g., common snook Centropomus undecimalis,

Appendix, Table 6).

I found seasonal patterns in species richness at the Anclote and Little Manatee

Rivers, and diversity varied with season at the Anclote River. At both rivers, the season

and habitat effects were significant (all P < 0.05) for species richness, and the interaction

of season and habitat was not significant (both P > 0.13), allowing evaluation of only the

main effects. Mean richness was higher in the fall (6.3 and 6.3 species per transect) than

in the spring (3.3 and 3.7 species per transect) at the Anclote and Little Manatee Rivers,

respectively (all P < 0.05). Mean diversity was higher in the fall (2.13) than in the spring

(1.38) at the Anclote River. However, mean diversity did not vary between seasons at

the Little Manatee River (P = 0.17).

I also detected differences in richness among habitats at two of the three river

systems. For the Anclote River, overhanging terrestrial brush, exposed root-wads, and

large woody debris had greater mean species richness (all P < 0.1, Figure 4) and diversity

than sandbar habitat (all P < 0.1, Figure 4). Thus, it appeared that all complex habitat

types contained higher richness and diversity than sandbar habitats at the Anclote River.

At the Little Manatee River, aquatic plants contained higher mean richness than large

woody debris and overhanging terrestrial brush (both P < 0.02, Figure 4), but the other

habitat types did not differ with regard to richness. Fish diversity at the Little Manatee

River did not differ among habitat types (P = 0.29, Figure 5).









For the Manatee River, I found no differences in fish richness or diversity among

habitat types at the Manatee River upstream site (Figures 4 and 5, both P > 0.6), but

species richness was higher in large woody debris than the other habitats for the Manatee

River downstream site (P = 0.04, Figure 4). Fish diversity did not differ among habitat

types at either Manatee River site (both P > 0.51, Figure 5).

My habitat-specific electrofishing revealed several differences in fish richness,

whereas fish diversity varied with habitat only at the Anclote River. In general, relatively

complex habitat such as large woody debris and plants frequently harbored higher fish

richness than less complex habitats such as sandbars. The nearly homogeneous habitat

characteristics at the Manatee River upstream site probably contributed to the lack of

significant differences for this system.













Table 1. Mean and standard deviation (SD) of habitat parameters for utilized and
available habitat intervals at Anclote River and Manatee River downstream
and upstream sites. Depth is stream depth in m, Current is current velocity in
m/s, WDI is woody debris index, FWD is percent of interval volume occupied
by fine woody debris, and Plant is percent of interval volume inhabited by
aquatic macrophytes. Shaded blocks denote significant differences, as
indicated by MANOVA testing and comparison of least squares means,
between utilized and available habitat intervals for the corresponding habitat
parameter (All P < 0.1).
Utilized Available
River Parameter (D
x(SD) x(SD)
Depth 1.00(0.57) 0.83(0.45)
Current 0.01(0.01) 0.01(0.02)
Anclote WDI 3.22(3.16) 1.60(2.50)
FWD 17.84(13.59) 11.08(10.67)
Plant 0.89(3.19) 1.58(6.22)
Depth 0.71(0.30) 0.67(0.31)
Manatee Current 0.00(0.00) 0.00(0.00)
downstream WDI 5.94(5.14) 1.15(2.51)
FWD 13.19(7.28) 7.00(5.61)
Plant 1.53(3.99) 1.50(5.77)
Depth 1.67(0.71) 1.69(0.70)
Manatee Current 0.00(0.00) 0.00(0.00)
upstream WDI 0.64(1.46) 0.60(1.28)
FWD 6.92(7.78) 9.88(13.64)
Plant 18.46(13.96) 27.75(23.87)










Table 2. Mean and standard deviation (SD) of habitat parameters for utilized and available habitat intervals per season and year for
Little Manatee River. Depth is stream depth in m, Current is current velocity in m/s, WDI is woody debris index, FWD is
percent of interval volume occupied by fine woody debris, and Plant is percent of interval volume inhabited by aquatic
macrophytes. Shaded blocks denote significant differences, as indicated by MANOVA testing and comparison of least
squares means, between utilized and available habitat intervals for the corresponding habitat parameter (All P < 0.1).
First Second
Fall Spring Fall Spring
Parameter Utilized Available Utilized Available Utilized Available Utilized Available
x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD)
Depth 0.89(0.47) 0.65(0.44) 0.88(0.51) 0.86(0.48) 0.75(0.41) 0.73(0.52) 0.76(0.37) 0.55(0.33)
Current 0.04(0.05) 0.03(0.05) 0.06(0.07) 0.05(0.06) 0.04(0.04) 0.04(0.04) 0.01(0.02) 0.01(0.02)
WDI 2.49(3.54) 1.28(2.08) 1.39(1.92) 1.24(1.84) 1.69(2.64) 0.88(1.35) 2.76(3.50) 1.00(1.48)
FWD 16.37(18.27) 10.75(13.09) 13.51(13.09) 12.14(11.66) 10.09(12.01) 10.00(9.69) 14.26(12.92) 9.80(12.86)
Plants 6.59(13.39) 8.25(18.10) 5.64(8.50) 6.29(14.26) 8.32(11.76) 3.80(6.97) 4.56(10.03) 5.00(10.93)











Table 3. Mean and standard deviation (SD) of habitat parameters for adult, juvenile, and
available habitat intervals at Anclote River and Manatee River downstream
and upstream sites. Depth is stream depth in m, Current is current velocity in
m/s, WDI is woody debris index, FWD is percent of interval volume occupied
by fine woody debris, and Plant is percent of interval volume inhabited by
aquatic macrophytes. Shaded blocks and differing letters denote significant
differences, as indicated by MANOVA testing and comparison of least
squares means, among interval types (All P < 0.1).
Adult Juvenile Available
River Parameter -( -(
x (SD) x(SD) x(SD)
A A B
epth (m) 1.04(0.58) 0.95(0.55) 0.83(0.45)
A BC AC
Current (m/s)
0.011(0.02) 0.006(0.01) 0.011(0.02)
Anclote WDI A B C
3.43(3.23) 2.89(3.04) 1.60(2.50)
A A B
FW D (P VI)------- ------
FWD (PV) 17.30(13.72) 18.68(13.40) 11.08(10.67)
A A A
Plant (PVI) A A A
Plant (PV) (0.67)2.51 (1.23)4.02 1.58(6.22)
A A A
Depth (m) 0.73(0.30) 0.64(0.25) 0.67(0.32)

Current (m/s)A 00A 00A
0.00(0.00) 0.00(0.00) 0.00(0.00)
Manatee A A B
downstream 6.05(5.05) 5.42(5.78) 1.15(2.51)
A A B
FWD (PVI) A A B
13.50(7.32) 11.67(7.18) 7.00(5.61)
A B A
Plant (PVI) 1.00(3.03) 4.17(6.69) 1.50(5.77)
A A A
Depth (m) 1.57(0.66) 1.86(0.79) 1.69(0.70)

Current (m/s)A 00A 00A
0.00(0.00) 0.00(0.00) 0.00(0.00)
Manatee WDI A A A
upstream 0.77(1.60) 0.38(1.10) 0.60(1.28)
A A A
FWD (PVI) A A A
FWD (PVI) 8.08(8.41) 4.62(5.82) 9.88(13.64)
A A A
Plant (PVI) 16.92(13.07) 21.54(15.41) 27.75(23.87)












Table 4. Mean and standard deviation (SD) of habitat parameters for adult, juvenile, and available habitat intervals per season and
year at Little Manatee River. Depth is stream depth in m, Current is current velocity in m/s, WDI is woody debris index,
FWD is percent of interval volume occupied by fine woody debris, and Plant is percent of interval volume inhabited by
aquatic macrophytes. Shaded blocks and differing letters denote significant differences, as indicated by MANOVA testing
and comparison of least squares means, among interval types (All P < 0.1).
First Second
Fall Spring Fall Spring
Adult Juvenile Available Adult Juvenile Available Adult Juvenile Available Adult Juvenile Available
x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD) x (SD)
A AB B A AB B
Depth 0.92(0.47) 0.80(0.47) 0.65(0.44) 0.93(0.53) 0.75(0.43) 0.86(0.48) 0.73(0.43) 0.80(0.33) 0.73(0.52) 0.82(0.39) 0.68(0.33) 0.55(0.33)

Current
0.04(0.05) 0.03(0.04) 0.03(0.05) 0.06(0.07) 0.06(0.06) 0.05(0.06) 0.03(0.03) 0.06(0.05) 0.04(0.05) 0.02(0.02) 0.01(0.02) 0.01(0.02)
A AB B
W D I ~___B
2.62(3.78) 2.06(2.61) 1.28(2.08) 1.60(2.06) 0.85(1.41) 1.24(1.84) 1.80(2.71) 1.27(2.37) 0.88(1.35) 3.17(3.49) 2.31(3.49) 1.00(1.48)

FWD A AB B
17.67(18.95) 12.19(15.39) 10.75(13.09) 13.68(12.57) 13.08(14.63) 12.14(11.66) 10.24(12.72) 9.55(8.99) 10.00(9.69) 15.83(13.81) 12.50(11.68) 9.80(12.86)

Plant
6.02(13.46) 8.44(13.22) 8.25(18.10) 4.71(7.62) 8.08(10.21) 6.29(14.62) 8.71(12.42) 6.82(8.94) 3.80(6.97) 4.03(9.59) 5.16(10.54) 5.00(10.93)







8 Anclote River

6

4L

2

0
-n Little Manatee River
E 4
E

J
S0
0


6
Manatee River downstream
4





May Sep Jan May Sep Jan May
2004 2005 2006
Figure 2. Hydrographs representing average daily stage (meters, mean sea level) data for
the Anclote, Little Manatee, and Manatee River downstream sites during the
two-year study period. Sampling periods at each system are indicated by red
arrows. Stage data were provide by T. Carson, U. S. Geological Survey.










1.0 Anclote River "*. Little Manatee River
S 0.8
.. ... ..... Utilized
.o 0.6 Available
I 0.4A .
0.2 *
*| o .o----" -- n . .. ..-
E
S1.0 .








0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0
o 0.6 "




0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0

Average Stage Decline (m)
Figure 3. Proportion of total habitat intervals per river with habitat remaining inundated
(y axis) with incremental decline in average river stage (m, x axis). Dotted
lines show habitat intervals utilized by spotted sunfish, and solid lines show
randomly located intervals representing overall available habitat. The dashed
red line signifies the 15% habitat loss value at each system











Anclote River
a a
a
T a








OTB Roots SB LWD

Manatee River downstream
a

ab ab -
TB Roots SB LWD





OTB Roots SB LWD


Little Manatee River
a

ab
Sab

bb






OTB Roots SB LWD Plants


Manatee River upstream



a


OTB LWD


Plants


Habitat Type


Figure 4. Box plots of fish species richness (y axis) for each system. Habitat types
including overhanging terrestrial brush (OTB), roots, sandbars (SB), large
woody debris (LWD), and aquatic plants (Plants) are shown (x axis).
Observations are from habitat-specific electrofishing transects. Differential
lettering denotes significant difference in group means, as indicated by
ANOVA testing and comparison of least squares means, among habitat types
(All P < 0.1). Median values are denoted by the horizontal mid-line within
the shaded region of each box. Upper and lower bounding horizontal lines of
the shaded region of each box denote the 75th and 25th percentile values.
Upper and lower box plot whiskers denote the 90th and 10th percentile values.
Dots lying beyond box plot whiskers denote the 95th and 5th percentile values.












a
a


.b

T


Anclote River


a


OTB Roots SB LWD

Manatee River downstream

a a a
j a '






OTB Roots SB LWD


3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0


3.5
3.0
2.5
2.0

1.5

1.0
0.5


Little Manatee River
a

aa








OTB Roots SB LWD Plants

Manatee River upstream



a
a a


OTB LWD


Plants


Habitat Type



Figure 5. Box plots of fish diversity (y axis) for each system. Habitat types including
overhanging terrestrial brush (OTB), roots, sandbars (SB), large woody debris
(LWD), and aquatic plants (Plants) are shown (x axis). Observations are from
habitat-specific electrofishing transects. Differential lettering denotes
significant difference in group means, as indicated by ANOVA testing and
comparison of least squares means, among habitat types (All P < 0.1).
Median values are denoted by the horizontal mid-line within the shaded
region of each box. Upper and lower bounding horizontal lines of the shaded
region of each box denote the 75th and 25th percentile values. Upper and
lower box plot whiskers denote the 90th and 10th percentile values. Dots lying
beyond box plot whiskers denote the 95th and 5th percentile values.


CI)


0

-j
--














CHAPTER 4
DISCUSSION

Spotted sunfish generally selected habitats with greater habitat complexity

compared to overall available habitat conditions. Woody debris habitats were frequently

selected by spotted sunfish, and the association with these habitats was the most common

of any of the habitat relationships that I measured. I also found spotted sunfish utilizing

aquatic plants as a habitat when plants were present and one instance of juveniles

selecting habitats of greater plant abundance relative to adults. Overall, spotted sunfish

appeared to be habitat generalists, with fish selecting areas of more complex habitat than

the available intervals (i.e., woody debris and/or aquatic plants). This generalist use of

habitat corresponds to several anecdotal reports that associate spotted sunfish with a

variety of habitats within Florida streams (Chable 1947; Kilby 1955; McLane 1955;

Caldwell et al. 1957) and is evident among other ecologically similar Florida Centrarchid

species. Hill and Cichra (2005) noted that the congeners such as warmouth sunfish L.

gulosus, redbreast sunfish L. auritus, and dollar sunfish L. marginatus have been

historically collected from a variety of lotic environments, and they described all of these

species as having been associated with woody debris, aquatic vegetation, and other

structurally complex habitat types.

Numerous investigators have noted the importance of woody debris habitats to fish

in lotic environments (Todd and Rabeni 1989; Fausch and Northcote 1992; Everett and

Ruiz 1993; Koehn et al. 1994; Flebbe and Dolloff 1995; Crook and Robertson 1999;

Horan et al. 2000; Dolloff and Warren 2003). Woody debris habitat offers refuge from









current velocity (McMahon and Hartman 1989; Shirvell 1990) and predators (Koehn et

al. 1994), and provides foraging (Benke et al. 1984; Smock et al. 1985) and ambush

locations for stream fishes (Matthews 1998). The current velocity measurements that I

recorded throughout the study were generally very low (range: 0 0.4 m/s), indicating

that refuge from flow velocity would likely have been a minor factor in spotted sunfish

habitat use. The body form and mouth morphology of spotted sunfish suggest that the

species is most suited to feeding on small prey items attached to substrate or drifting

within the water column (Carrol et al. 2004). Thus, it is much more likely that the

association of spotted sunfish with woody debris and complex habitats was attributable to

their use of these habitat types as foraging areas and refuge from predation rather than as

velocity refuge. However, during higher flows they may utilize woody debris as velocity

refuge.

Previous work surrounding the feeding ecology of spotted sunfish provides a

functional linkage between the species and complex habitats such as woody debris and

aquatic vegetation. As implied by their general morphology and relatively small size,

spotted sunfish feed primarily on aquatic insects and other invertebrates (Chable 1947;

McLane 1955; Caldwell et al.1957). Chable (1947) and McLane (1955) found 100% and

85% of their spotted sunfish diet samples, respectively, to contain insects. Prey taxa

frequently observed among spotted sunfish diet items include chironomidae, coleoptera,

trichoptera, ephemeroptera, and amphipoda (Chable 1947; McLane 1955; Caldwell et

al. 1957), all of which have been shown to be associated with complex habitats in Florida

streams (Warren et al. 2000; Steigerwalt 2005).









Across nearly all lotic environments, woody debris has been shown to provide

important habitat for aquatic invertebrates (Braccia and Batzer 2001; Benke and Wallace

2003). However, because of the general instability of sand and mud substrates in these

systems, the relative value of woody debris, root wad, and submerged vegetation to

stream ecosystems appears to increase in lowland rivers where these habitats offer the

most stable attachment sites for invertebrates (Benke et al. 1984; Smock et al. 1985.

Benke et al. (1985) showed that invertebrate communities derived from snag habitat were

a valuable source of prey items for Lepomis spp. and other stream fishes at Satilla River,

Georgia, and noted that snag fauna comprised at least 60% of diet composition for all

Lepomis spp., including spotted sunfish. Kelly et al. (2005) noted a similar linkage

between snag and root habitat derived invertebrate communities and redbreast sunfish

diet composition at the Alafia River, Florida. Caldwell et al. (1957) found large

quantities of periphyton among spotted sunfish stomachs and indicated that it was

representative of the attached algal community growing on leaves of locally abundant

Sagittaria at the Silver River, Florida. They suggested that the periphyton were most

likely incidentally consumed while feeding on attached invertebrates among these

vegetation beds. McLane (1955) also found filamentous algae to be a large component

(26.9 % by occurrence) of spotted sunfish diet at the St. Johns River, Florida.

Complex habitat such as woody debris and aquatic vegetation also provides refuge

from predators for juvenile or small bodied fishes such as Lepomis spp. (Savino and Stein

1982; Everett and Ruiz 1993; Crook and Robertson 1999; Dolloff and Warren 2003).

Juvenile bluegill sunfish tend to select complex habitats (i.e., aquatic plants or artificial

aquatic plants) in the presence of potential predators and this behavior often results in









reduced predation success (Savino and Stein 1982; Werner et al. 1983; Gotceitas and

Colgan 1987; Johnson et al.1988). Because the coastal rivers of Florida contain a variety

of freshwater and marine piscivores, and spotted sunfish remain relatively small even as

adults, the availability of complex habitat is probably important as refuge from predation.

Largemouth bass and/or common snook were abundant in all our sample rivers, and loss

of complex habitat would likely expose spotted sunfish to higher mortality rates via

predation (e.g., Savino and Stein 1982).

Habitat requirements of adults and juveniles of a species often differ (Larkin 1978;

Werner and Gilliam 1984; Halpern et al. 2005). Ontogenetic shifts in habitat utilization

have been observed among various lotic fishes, such as Roanoke logperch Percina rex

(Rosenberger and Angermeier 2003), river blackfish Gadopsis marmoratus (Koehn et al.

1994), creek chub Semotilus atromaculatus (Magnan and FitzGerald 1984), and several

Salmonid species (Moore and Gregory 1988; McMahon and Hartman 1989; Nickelson et

al. 1992). I identified one instance of juvenile spotted sunfish using greater aquatic plant

densities relative to adults. However, the general pattern was that adult and juvenile

spotted sunfish occupied similar habitat types, and I found few significant differences

between habitat parameters collected for adult and juvenile lifestages. The overall

similarity in adult and juvenile spotted sunfish habitat utilization patterns corresponded to

McMahon's (1984) description of habitat use of a congener, warmouth sunfish.

Mittlebach (1984) noted that pumpkinseed sunfish L. gibbosus tend to occupy similar

habitat types throughout their ontongeny, but overall few studies have specifically

addressed comparisons of habitat utilization between adult and juvenile lifestages of

Lepomis spp. (see Hill and Cichra 2005).









Although it represents a single occurrence in my results, the use of higher plant

densities by juveniles relative to adults is not surprising. Lobb and Orth (1991) also

found associations of juvenile stream fish species with in-stream vegetation. Similarly,

Hellier (1966) observed a pattern in use of vegetation by juvenile redbreast sunfish in a

Florida river. Juvenile bluegill sunfish have been observed using complex habitats that

offer abundant and relatively small interstitial spaces, much like those created by dense

aquatic vegetation, as a refuge from predation (Savino and Stein 1982; Werner et al.

1983; Gotceitas and Colgan 1987; Johnson et al. 1988).

At Anclote and Little Manatee Rivers, I found that habitat intervals occupied by

spotted sunfish exhibited greater depth values relative to the available habitat intervals.

The outer edge of stream bends typically corresponded to areas of greater depth found in

close proximity to the bank, and these locations may provide an important component of

spotted sunfish habitat. These areas would be subjected to greater substrate erosion

during periods of increased streamflow; thus, creating localized abundances of exposed

root-wads and fallen woody debris. Deeper areas along the bank may also be more

resilient to fluctuations in river stage, thus, providing habitat that remains inundated

throughout daily tidal changes.

My identification of spotted sunfish habitat selection was likely largely dependent

on changes in density of the species across habitat types. Van Horne (1983) stressed that

the assumption that greater density of a species within a particular habitat type translates

into greater quality of that habitat type may not always hold true. Evaluation of habitat

quality should consider spatial changes in species density, but it must also consider

comparisons of survival and reproductive contribution by individuals occupying differing









habitats (Van Home 1983). For example, social interactions among individuals of a

species may create instances where subdominant individuals, exhibiting reduced survival

and reproductive output relative to dominant individuals, occupy sub-optimal habitats at

high densities (population sink). In this situation, sustenance of the local population may

be reliant upon a few dominant individuals, exhibiting high survival rate and reproductive

output, that occupy the best habitat (population source) at a relatively low density. Thus,

relying solely on abundance as an indicator of habitat quality may lead to erroneous

conclusions in the identification of quality habitats (Van Home 1983). My study

addressed patterns in habitat use and selection by spotted sunfish in Florida Rivers, but I

did not investigate demographic patterns such as individual survival rates or reproductive

contribution in relation to stream habitat types. Thus, although my identification of

utilized and selected habitat characteristics may be representative of important or

required spotted sunfish habitat, the habitat associations revealed here may not infer

differences in fish survival and growth had these habitats been lost from the system.

Experimental manipulations would be required to elucidate the impacts of habitat change

on fish vital rates.

Rogers et al. (2005) found that spotted sunfish abundance was positively related to

river stage at the Ocklawaha River, Florida, with high fish abundances in years following

high stage the previous year. I did not evaluate inter-annual trends in spotted sunfish

abundance in this study, but the habitat use and selections patterns that I identified help

explain the mechanisms for the relationship reported by Rogers et al. (2005). High water

levels inundate complex habitats, likely providing food and refuge for spotted sunfish.

Conversely, years with low water levels would reduce habitat availability possibly









leading to lower spotted sunfish abundance via food limitation, predation, or a

combination of these factors. Bonvechio and Allen (2005) found that redbreast sunfish

year class strength was also positively related to river flows in Florida, and the

relationship for Lepomis spp. may extend across several members of the genus.

My simulations indicated that relatively small decreases in river stage (e.g., average

0.30 m decline) below base-flow conditions could result in up to 20% reduction in habitat

availability. Kelly et al. (2005) identified MFL strategies for the Alafia River, Florida,

based on periods of varying seasonal flows through the year. My samples were

conducted during their Blocks 1 and 3, which represent the spring and fall seasons

typically exhibiting relatively low flows and stage. Water levels and flows during my

sampling events were relatively low at about base-flow conditions (refer to Figure 2).

My habitat measurements suggested that relatively minor declines in average river stage

at base flow conditions could reduce overall habitat availability beyond the 15%

benchmark used by the Southwest Florida Water Management District to signify

undesirable resource loss (Kelly et al. 2005). However, these habitat loss simulations

may not accurately reflect changes in shoreline habitat availability during long term

(multi-year) stage and streamflow declines. Long term decreases in flow regime would

redefine stream margins in response to new water level trends, and riparian vegetation

would colonize newly exposed banks, thus, allowing for continued recruitment of

complex habitats derived from terrestrial sources. Furthermore, long term changes in

river stage and steamflow trends may provide conditions conducive to aquatic plant

colonization, also creating new complex habitats for stream fishes. Considering these









limitations, I advocate that my simulations are likely best suited to estimate habitat loss

during short-term (< 1-2 years) declines in average daily stage.

I did not evaluate the potential effect of low river flow and stage on habitat loss via

saltwater intrusion. Stream channel elevation was relatively low within all of my

sampling reaches, and with the exception of those on the Manatee River upstream of the

Lake Manatee Dam, many of my sampling reaches were at least somewhat tidally

influenced. It is possible, under conditions of persistent low freshwater discharge, that

water level in my study areas would remain stable if saline water from the downstream

estuary encroached upstream, resulting in a different form of habitat loss for freshwater

fish communities than I measured. Catalano et al. (2006) found saltwater intrusion to

significantly reduce available habitat for freshwater fishes in the Lower Hillsborough

River, Florida when flows declined. Estevez and Marshall (1994) noted changes in

historical isohaline and vegetation patterns in the Manatee River estuary following

implementation of flow regulation via a dam on the Manatee River, Florida. I did not

find high salinity waters in the Anclote, Little Manatee, or Manatee downstream sites

during this study, with freshwater fishes present during all sampling events. However,

location and movement of isohalines within the shallow bays and lagoons of the Gulf of

Mexico are considered especially susceptible to the effects of fluctuating freshwater flow

inputs (Sklar and Browder 1998). Therefore, saltwater intrusion should be considered as

another potential form of habitat loss for freshwater/oligohaline fishes in these coastal

river systems, and defining the extent of potential saltwater intrusion is needed for these

systems.









My sampling design incorporated sampling along the bank of each river, and it is

possible that mid-channel habitat could have influenced habitat availability for spotted

sunfish. However, these rivers are relatively shallow (< 2 meters) and narrow (i.e., < 50

meters wide) with shifting of sediments occurring during high flood events. The mid

channel areas of the rivers were largely devoid of woody debris and aquatic plants.

Nevertheless, my evaluation of habitat availability for spotted sunfish should be viewed

as conservative, as not all sections of the rivers were sampled for habitat availability and

fish occurrence.

My habitat-specific community sampling indicated that not only are complex

habitat types selected for by spotted sunfish but that they tend to harbor greater species

richness relative to other habitat types as well. Fish species richness varied among

habitat types for all sampling rivers except the Manatee River upstream site. The specific

habitat types that contained the highest fish richness varied among rivers, but fish

richness was generally highest in either large woody debris (Anclote River and Manatee

River downstream) or plant habitats (Little Manatee River). These results were similar to

those of Lobb and Orth (1991), who found highest stream fish densities in and adjacent to

snags relative to other habitats in a warmwater Virginia stream. Rogers et al. (2005)

found that spotted sunfish abundance was related to fish richness across years at the

Ocklawaha River, Florida. The habitat relationships I identified supported this

relationship because both spotted sunfish occurrence and total richness were highest in

the complex habitats at each system. I was unable to detect differences in fish diversity

among habitat types in most cases, suggesting that fish diversity may be a less effective

metric for detecting change in fish communities than species richness.









I acknowledge that my use of electrofishing as a sampling technique may introduce

some inherent biases into data collected for spotted sunfish habitat intervals (e.g., Bain

and Finn 1991). Efficacy of electrofishing is inversely related to depth and complexity of

some habitat types (i.e., dense vegetation) (Bayley and Austen, 2002). These tendencies

may have biased locations of spotted sunfish toward areas of shallower depth and away

from areas of dense aquatic plants or overhanging brush. However, I directed sampling

effort along river banks to minimize the effects of depth on capture efficiency. When

subjected to an electromagnetic field, fish may exhibit varied responses. Of some

concern were positive electrotaxis, the movement of a fish toward the electrofisher anode,

negative electrotaxis, and fright response, the latter two of which would result in

movements of a fish away from the electrofisher electromagnetic field (Bain and Finn

1991; Reynolds 1996). Any of these results could have affected the spatial accuracy of

spotted sunfish habitat intervals. However, I made efforts to locate spotted sunfish

intervals at the point where an individual was first seen within the electromagnetic field.

If I suspected that substantial electrotaxis had occurred by an individual, it was not used

for habitat data collection. Additionally, I felt that use of a one meter radius for habitat

intervals provided sufficient volume of measured habitat that it would remain

representative of an individual's true habitat occurrence if limited electrotaxis did occur.

Electrofishing efficiency also increases with fish size (Reynolds 1996), suggesting that

juvenile spotted sunfish were likely not collected as efficiently as adults. However,

because my goal was to measure the habitat associations, the relative comparisons among

habitat types at each system were meaningful.









In summary, I identified habitat use and selection patterns for spotted sunfish but

found them to be fairly general in their habitat associations. Few differences were found

between adult and juvenile habitat use patterns, indicating that the generalist use of

habitats likely persists throughout spotted sunfish ontongeny. My results suggest that

seemly minor changes in the average stage during fall and spring seasons may

substantially reduce the availability of habitats used by spotted sunfish. Spotted sunfish

appeared to be a good indicator of fish richness differences among habitat types,

suggesting that protection of complex habitats will also benefit the whole fish community

in southwest Florida Rivers.















APPENDIX
SAMPLING LOCATIONS AND COMMUNITY SUMMARY

Table 5. Latitude and longitude coordinates for spotted sunfish sampling reaches at
Anclote, Little Manatee, and Manatee Rivers, Florida. Upstream refers to
upstream reach boundaries and Downstream refers to downstream reach
boundaries.
River Reach Upstream Downstream
SN 28012.382' N 28012.311'
W 82042.527' W 82042.656'
N 28012.270' N 28012.199'
W 82042.660' W 82042.803'
N 28012.167' N 28011.946'
W 82042.806' W 82042.826'
N 27040.531' N 27040.673'
W 82022.523' W 82022.768'
N 27040.569' N 27040.569'
W 82022.787' W 82023.010'
Little Manatee N 27040.536' N 27040.435'
W 82023.012' W 82023.214'
N 27040.097' N 27039.956'
W 82023.411' W 82023.350'
N 27039.898' N 27039.888'
W 82023.430' W 82023.691'
N 27027.887' N 27027.997'
W 82014.973' W 82015.171'
Manatee N 27027.987' N 27028.077'
upstream W 82015.186' W 82015.468'
N 27028.089' N 27028.109'
W 82015.490' W 82015.666'
N 27029.779' N 27029.964'
W 82021.431' W 82021.546'
Manatee N 27030.023' N 27030.275'
downstream W 82021.631' W 82021.679'
N 27030.323' N 27030.563'
W 82021.637' W 82021.683'

















Table 6. Habitat-specific list of fish species collected from the Anclote (A), Little Manatee (L), Manatee upstream (U) and Mantee
downstream (D) rivers.
Overhanging
Roots Snags Brush Plants Sandbars

Family Species A L D A L U D A L U D L U A L D
Florida gar
Lepisosteus platyrincus X X X X X X X X X X X X
Lepisosteidae
Longnose gar
L. osseus X X X X X X X X
Amiidae Bowfin
Amidae Am.a calva X X X X X X
AmIa calva I I I A
.,. ,American eel
Anquillidae Angula rostrata X X X X

Synbranchidae Asian swamp eel
Monopterus albus X X

Golden shiner
Notemegonus crysoleucas X X X X
Cyprinidae Taillight shiner
Notropis maculatus X X X X

Coastal shiner
N. petersonz X X X X X X X X X X X X X
Lake chubsucker
Catostomidae Erxyon sucetta X X
Erimyzon sucetta
Channel catfish
Ictalurus punctatus X X
Ictaluridae
Brown bullhead
Amezurus nebulosus X X
Clariidae Walking catfish
Clarzas batrachus X
Bluefin killifish
Lucanza goodez X X X X X
Rainwater killifish
L. parva X
Fundulidae L. parva X
Golden topminnow
Fundulus chrysotus X
Seminole Killifish
F. seminolis X X X

















Overhanging
Roots Snags Brush Plants Sandbars

Family Species A L D A L U D A L U D L U A L D

Gambusia sp. X X X X X X X X X X X X
Poeciliidae
Sailfin molly
Poecilia latipinna X X X X X
Banded pygmy sunfish
Ellasoma zonatum X
Ellasomatidae
Everglades pygmy sunfish
E. evergladet X
Largemouth bass
Micropterus salmoides X X X X X X X X X X X X X X
Bluegill sunfish
Lepomis macrochirus X X X X X X X X X X X X X X X
Dollar sunfish
L. marginatus X X X X
Redbreast sunfish
L. auritus X
Centrarchidae
Redear sunfish
L. mucrolophus X X X X X X X X X X X X
Spotted sunfish
L. punctatus X X X X X X X X X X X X
Warmouth sunfish
L. gulosus x x X x x X
Bluespotted sunfish
Enneacanthus glortosus X X
Black acara
Cichlasoma bimaculatum X
Cichlidae
Blue tilapia
Oreochromis aurea X
Brook silverside
Labidesthes sicculus X X
Atherinopsidae
Inland silverside
Menidia ', i. ,, X
Striped mullet
Mugillidae Mugil cephalus X X X X X X X

















Overhanging
Roots Snags Brush Plants Sandbars

Family Species A L D A L U D A L U D L U A L D
Naked goby
Gobiosoma bosc X X
Gobiidae
River goby
Awaous banana X

Achiridae Hogchoker
Trinectes maculatus X X X X X X X X X

Eleotridae Fat sleeper
Dormitator maculatus
enropomae Common snook
Centropomidae Centropomus undecmas X X X X X X

Lutjiae Mangrove snapper
Lutjanus grzseus















LIST OF REFERENCES


Anderson, N. H., J. R. Sedell, L. M. Roberst, and F. J. Triska. 1978. The role of aquatic
invertebrates in processing of wood debris in coniferous forest streams. American
Midland Naturalist 100:64-82.

Angermeier, P. L., and J. R. Karr. 1984. Relationships between woody debris and fish
habitat in a small warmwater stream. Transactions of the American Fisheries
Society 113:716-726.

Bailey, R. M., H. E. Winn, and C. L. Smith. 1954. Fishes from the Escambia River,
Alabama and Florida. Proceedings of the Academy of Natural Sciences of
Philadelphia 106:109-164.

Bain, M. B., and J. T. Finn. 1991. Analysis of microhabitat of fish: investigator effect
and investigator bias. Rivers 2(1):57-65.

Bain, M. B., J. T. Finn, and H. E. Brooke. 1988. Streamflow regulation and fish
community structure. Ecology 69:382-392.

Bass, D. G., and D. T. Cox. 1985. River habitat and fishery resources of Florida. Pages
122-188 in W. Seaman Jr., editor. Florida aquatic habitat and fishery resources.
American Fisheries Society, Florida Chapter, Eustis, Florida.

Bayley, P. B., and D. J. Austen. 2002. Capture efficiency of a boat electrofisher.
Transactions of the American Fisheries Society 131: 435-451.

Benke, A. C., R. L. Henry, III, D. M. Gillespie, and R. J. Hunter. 1985. Importance of
snag habitat for animal production in southeastern streams. Fisheries 10(5):8-13.

Benke, A. C., T. C. Van Arsdall, Jr., D. M. Gillespie, and F. K. Parrish. 1984.
Invertebrate productivity in a subtropical blackwater river: the importance of
habitat and life history. Ecological Monographs 54: 25-63.

Benke, A. C., and J. B. Wallace. 2003. Influence of wood on invertebrate communities
in streams and rivers. Pages 149-177 in S. Gregory, K. Boyer, and A. Gurnell,
editors. The ecology and management of wood in world rivers. American
Fisheries Society, Bethesda, Maryland.

Bonvechio, T. F., and M. S. Allen. 2005. Relations between hydrological variables and
year-class strength of sportfish in eight Florida waterbodies. Hydrobiologia
532:193-207.









Braccia, A., and D. P. Batzer. 2001. Invertebrates associated with woody debris in a
Southeastern U. S. forested floodplain wetland. Wetlands 21:18-31.

Caldwell, D. K., H. T. Odum, T. R. Hellier, Jr., and F. H. Berry. 1957. Populations of
spotted sunfish and Florida largemouth bass in a constant-temperature spring.
Transactions of the American Fisheries Society 85:120-134.

Carlander, K. D. 1977. Handbook of freshwater fishery biology, Volume 2. Iowa State
University Press, Ames, Iowa.

Carrol, A. M., P. C. Wainwright, S. H. Huskey, D. C. Collar, and R. G. Turingan. 2004.
Morphology predicts suction feeding performance in centrarchid fishes. The
Journal of Experimental Biology 207:3873-3881.

Catalano, M. J., M. S. Allen, and D. J. Murie. 2006. Effects of variable flows on water
chemistry gradients and fish communities at Hillsborough River, Florida. North
American Journal of Fisheries Management 26:108-118.

Chable, A. C. 1947. A study of the food habits and ecological relationships of the
sunfishes of northern Florida. Master's thesis. The University of Florida,
Gainesville, Florida.

Crook, D. A., and A. I. Robertson. 1999. Relationships between riverine fish and woody
debris: implications for lowland rivers. Marine and Freshwater Research 50:941-
953.

Cushman, R. M. 1985. Review of ecological effects of rapidly varying flows
downstream of hydroelectric facilities. North American Journal of Fisheries
Management 5:330-339.

Dolloff, D. A., D. G. Hankin, and G. H. Reeves. 1993. Basinwide estimation of habitat
and fish populations in streams. U. S. Forest Service. General Technical Report
SE-83. Asheville, North Carolina.

Dolloff, C. A., and M. L. Warren, Jr. 2003. Fish relationships with large wood in small
streams. Pages 179-193 in S. Gregory, K. Boyer, and A. Gurnell, editors. The
ecology and management of wood in world rivers. American Fisheries Society,
Bethesda, Maryland.

Estevez, E. D., and M. J. Marshall. 1994. Impact of flow variation in the Manatee River,
section 2. Biological assessment of pre- and post-alterations. Flows and salinities.
Tampa Bay National Estuary Program Technial Pbulication 09-94. Prepared by
Mote Marine Laboratory for Dames and Moore, Inc., Tampa Bay National Estuary
Program.

Evertt, R. A., and G. M. Ruiz. 1993. Coarse woody debris as a refuge from predation in
aquatic communities. Oecologia 93:475-486.









Fausch, K. D., and T. G. Northcote. 1992. Large woody debris and Salmonid habitat in
a small coastal British Columbia stream. Canadian Journal of Fisheries and
Aquatic Sciences 49:682-693.

Flebbe, P. A., and C. A. Dolloff. 1995. Trout use of woody debris and habitat in
Appalachian wilderness streams of North Carolina. North American Journal of
Fisheries Management 15:579-590.

Gotceitas, V., and Colgan, P. 1987. Selection between densities of artificial vegetation
by young bluegills avoiding predation. Transactions of the American Fisheries
Society 116:40-49.

Halpern, B. S., S. D. Gaines, and R. R. Warner. 2005. Habitat size, recruitment, and
longevity as factors limiting population size in stage-structured species. The
American Naturalist 165:82-94.

Hellier, T. R., Jr. 1966. Fishes of the Santa Fe River system. Bulletin of the Florida
State Museum 11:1-46.

Hill, J. E., and C. E. Cichra. 2005. Biological synopsis of five selected Florida
Centrarchid fishes with an emphasis on the effects of water level fluctuations. St.
Johns Water Management District. Special Publication SJ2005-SP3. Palatka,
Florida.

Horan, D. L., J. L. Kershner, C. P. Hawkins, and T. A. Crowl. 2000. Effects of habitat
area and complexity on Colorado River cutthroat trout density in Uinta Mountains
streams. Transactions of the American Fisheries Society 129:1250-1263.

Hubbs, C. L., and E. R. Allen. 1943. Fishes of Silver Springs, Florida. Proceedings
Florida Academy of Sciences 6:110-130.

Irvine, J. R. 1985. Effects of successive flow perturbations on stream invertebrates.
Canadian Journal of Fisheries and Aquatic Sciences 42:1922-1927.

Johnson, D. L., R. A. Beaumier, and W. E. Lynch, Jr. 1988. Selection of habitat
structure interstice size by bluegills and largemouth bass in ponds. Transactions of
the American Fisheries Society 117:171-179.

Kelly, M., A. Munson, J. Morales, and D. Leeper. 2005. Alafia River flows and levels;
freshwater segment. Final Report, Southwest Florida Water Management District,
Brooksville, Florida.

Kelsch, S. W. 1994. Lotic fish-community structure following transition from severe
drought to high discharge. Journal of Freshwater Ecology. 9:331-341.

Kilby, J. D. 1955. The fishes of two Gulf Coast marsh areas of Florida. Tulane Studies
in Zoology 2:175-247.









Kinsolving, A. D., and M. B. Bain. 1993. Fish assemblage recovery along a riverine
disturbance gradient. Ecological Applications 3:531-544.

Koehn, J. D., N. A. O'Connor, and P. D. Jackson. 1994. Seasonal and size-related
variation in microhabitat use by a southern Victorian stream fish assemblage.
Australian Journal of Freshwater Research 45:1353-1366.

Larkin, P. A. 1978. Fisheries management an essay for ecologists. Annual Review of
Ecology and Systematics 9:57-73.

Lobb, M. D., and D. J. Orth. 1991. Habitat use by an assemblage of fish in a large
warmwater stream. Transactions of the American Fisheries Society 120:65-78.

Magnan, P., and G. J. FitzGerald. 1984. Ontogenetic changes in diel activity, food
habits, and spatial distribution of juvenile and adult creek chub, Semotilus
atromaculatus. Environmental Biology of Fishes 11:301-307.

Matthews, W. J. 1998. Patterns in freshwater fish ecology. Chapman and Hall, New
York, New York.

McLane, W. M. 1955. The Fishes of the St. Johns River system. Doctoral dissertation.
The University of Florida, Gainesville, Florida.

McMahon, T. E., G. Gebhart, 0. E. Maughan, and P. C. Nelson. 1984. Habitat
suitability index models and instream flow suitability curves: warmouth.
FWS/OBS-82.10.67. U. S. Fish and Wildlife Service, Washington, D.C.

McMahon, T. E., and G. F. Hartman. 1989. Influence of cover complexity and current
velocity on winter habitat use by juvenile coho salmon (Oncorhynchus kisutch).
Canadian Journal of Fisheries and Aquatic Sciences 46:1551-1557.

Mittelbach, G. G. 1984. Predation and resource partitioning in two sunfishes
(Centrarchidae). Ecology 65:499-513.

Moore, K. M. S., and S. V. Gregory. 1988. Summer habitat utilization and ecology of
cutthroat trout fry (Salmo clarki) in Cascade Mountain streams. Canadian Journal
of Fisheries and Aquatic Sciences 45:1921-1930.

Nickelson, T. E., J. D. Rodgers, S. L. Johnson, and M. F. Solazzi. 1992. Seasonal
changes in habitat use juvenile coho salmon (Oncorhyncus kisutch) in Oregon
coastal streams. Canadian Journal of Fisheries and Aquatic Sciences 49:783-789.

Peters, J. C. 1982. Effects of river and streamflow alteration on fishery resources.
Fisheries 7(2):20-22.

Power, G., R. S. Brown, and J. G. Imhof. 1999. Groundwater and fish insights from
northern North America. Hydrological Processes 13:401-422.









Raibley, P. T., T. M. O'Hara, K. S. Irons, K. D. Blodgett, and R. E. Sparks. 1997.
Largemouth bass size distributions under varying annual hydrological regimes in
the Illinois River. Transactions of the American Fisheries Society 126:850-856.

Reynolds, J. B. 1996. Electrofishing. Pages 221-253 in B. R. Murphy and D. W. Willis,
editors. Fisheries Techniques, 2nd Edition. American Fisheries Society, Bethesda,
Maryland.

Rogers, M. W., M. S. Allen, and M. D. Jones. 2005. Relationships between river surface
levels and fish assemblages in the Ocklawaha River, Florida. River Research and
Applications 21:501-511.

Rosenberger, A., and P. L. Angermeier. 2003. Ontogenetic shifts in habitat use by the
endangered Roanoke logperch (Percina rex). Freshwater Biology 48:1563-1577.

Rosenfeld, J. 2003. Assessing the habitat requirements of stream fishes: an overview
and evaluation of different approaches. Transactions of the American Fisheries
Society 132:953-968.

Rozas, L. P., and W. E. Odum. 1988. Occupation of submerged aquatic vegetation by
fishes: testing the roles of food and refuge. Oecologia 77:101-106.

SAS Institute. 2002. SAS Users Guide: Statistics, Version 8, 4th edition. SAS Institute,
Cary, North Carolina.

Savino, J. F., and R. A. Stein. 1982. Predator-prey interaction between largemouth bass
and bluegills as influenced by simulated submersed vegetation. Transactions of the
American Fisheries Society 111:255-266.

Scheaffer, R. L., W. Mendenhall, and L. Ott. 1990. Elementary survey sampling, 4th
edition. PWS-KENT, Boston, Massachusetts.

Schlosser, I. J. 1985. Flow regime, juvenile abundance, and the assemblage structure of
stream fishes. Ecology 66:1484-1490.

Shirvell, C. S. 1990. Role of insteam rootwads as juvenile coho salmon (Oncorhyncus
kisutch) and steelhead trout (0. mykiss) cover habitat under varying steamflows.
Canadian Journal of Fisheries and Aquatic Sciences 47:852-861.

Simonson, T. D., J. Lyons, and P. D. Kanehl. 1994. Quantifying fish habitat in streams:
transect spacing, sample size, and a proposed framework. North American Journal
of Fisheries Management 14:607-615.

Sklar, F. H., and J. A. Browder. 1998. Coastal environmental impacts brought about by
alterations to freshwater flow in the Gulf of Mexico. Environmental Management
22:547-562.









Smock, L. A., E. Gilinsky, and D. L. Stoneburner. 1985. Macroinvertebrate production
in a southeastern United States blackwater stream. Ecology 66: 1491-1503.

Steigerwalt, N. M. 2005. Environmental factors affecting aquatic invertebrate
community structure on snags in the Ichetucknee River, Florida. Master's thesis.
The University of Florida, Gainesville, Florida.

Todd, B. L., and C. F. Rabeni. 1989. Movement and habitat use by stream-dwelling
smallmouth bass. Transactions of the American Fisheries Society 118:229-242.

Travnichek, V. H., M. B. Bain, and M. J. Maceina. 1995. Recovery ofa warmwater fish
assemblage after the initiation of a minimum-flow release downstream from a
hydroelectric dam. Transactions of the American Fisheries Society 124:836-844.

Tyus, H. M. 1990. Effects of altered streamflows on fishery resources. Fisheries
15(3):18-20.

Van Home, B. 1983. Density as a misleading indicator of habitat quality. Journal of
Wildlife Management 47:893-901.

VanderKooy, K. E., C. F. Rakocinski, and R. W. Heard. 2000. Trophic relationships of
three sunfishes (Lepomis spp.) in an estuarine bayou. Estuaries 23:621-632.

Warren, G. L., D. A. Holt, C. Cichra, and D. VanGenecten. 2000. Fish and aquatic
invertebrate communities of the Wekiva and Little Wekiva Rivers: a baseline
evaluation in the context of Florida's minimum flows and levels statues. St. Johns
River Water Management District Special Publication SJ2000-SP4, Palatka,
Florida.

Werner, E. E., and J. F. Gilliam. 1984. The ontogenetic niche and species interactions in
size-structured populations. Annual Reviews in Ecology and Systematics 15:393-
425.

Werner, E. E., J. F. Gilliam, D. J. Hall, and G. G. Mittelbach. 1983. An experimental
test of the effects of predation risk on habitat use in fish. Ecology 64:1540-1548.

Weyers, R. S., C. A. Jennings, and M. C. Freeman. 2003. Effects of pulsed, high-
velocity water flow on larval robust redhorse and v-lip redhorse. Transactions of
the American Fisheries Society 132:84-91.

Wheeler, A. P., and M. S. Allen. 2003. Habitat and diet partitioning between shoal bass
and largemouth bass in the Chipola River, Florida. Transactions of the American
Fisheries Society 132:438-449.















BIOGRAPHICAL SKETCH

Andrew (Drew) Carl Dutterer was born on October 17, 1979, in Athens, Georgia.

In 1984 he and his family relocated to the North Carolina foothills, just outside of the

small town of Dallas. Drew enrolled at North Carolina State University following

graduation from high school in 1998. While attending N.C. State, Drew received a

bachelor's degree in environmental sciences, with an emphasis in ecology. In 2004,

Drew enrolled at the University of Florida to pursue a Master of Science degree, while

conducting research through the Department of Fisheries and Aquatic Sciences. He

completed his graduate studies with the University of Florida in the summer of 2006.

Drew is a washed-up artist, closet musician, incompetent outboard mechanic, swell cook,

and fair biologist. First and foremost, however, he is an avid outdoorsman and for most

of his life fishing has been a passion, presenting that insatiable itch to scratch.