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Activity patterns and habitat associations of Kemp's ridley turtles, Lepidochelys kempi, in the coastal waters of the Cedar Keys, Florida

Material Information

Title:
Activity patterns and habitat associations of Kemp's ridley turtles, Lepidochelys kempi, in the coastal waters of the Cedar Keys, Florida
Creator:
Schmid, Jeffrey Robert, 1964- ( Dissertant )
Percival, Henry F. ( Thesis advisor )
Lindberg, William ( Reviewer )
Zwick, Paul ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
2000
Language:
English
Physical Description:
xiii, 184 leaves : ill. (some col.), maps ; 29 cm.

Subjects

Subjects / Keywords:
Aquatic habitats ( jstor )
Crabs ( jstor )
Eggshells ( jstor )
Foraging ( jstor )
Habitat preferences ( jstor )
Keys ( jstor )
Mud ( jstor )
Sea turtles ( jstor )
Telemetry ( jstor )
Turtles ( jstor )
Dissertations, Academic -- Wildlife Ecology and Conservation -- UF
Ecosystem -- Florida ( mesh )
Environment -- Florida ( mesh )
Marine Biology -- Florida ( mesh )
Research ( mesh )
Turtles -- Florida ( mesh )
Veterinary Medicine ( mesh )
Wildlife Ecology and Conservation thesis, Ph. D
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Abstract:
Radio and sonic telemetry were used to investigate the site fidelity, tidal orientation, rate of movement (ROM), respiratory behavior, and habitat associations of Kemp's ridley turtles, Lepidochelys kempi. Nine turtles were tracked east of the Cedar Keys, Florida, for up to 70 days after release and occupied 5 - 30 km2 foraging ranges. The mean of mean turtle bearings on incoming (48+/-49 degrees) and falling (232+/-41 degrees) tides were significantly oriented to the mean directions of tidal flow (37+/-9 degrees, p<0.0025, and 234+/-9 degrees, p<0.005, respectively). Turtles had a mean ROM of 0.44+/-0.33 km/hr (range: 0.004 - 1.758 km/hr), a mean surface duration of 18+/-15 seconds (range: 1 - 88 seconds), and a mean submergence duration of 8.4+/-6.4 minutes (range: 0.2 - 60.0 minutes). ROM was negatively correlated with surface and submergence durations and positively correlated with the number of surfacings. Furthermore, ROMs were higher and surface and submergence durations were shorter during the day. Habitat associations of Kemp's ridley turtles were analyzed in terms of availability, utilization, and preference using compositional analyses. Forty-eight percent of the study area consisted of sand bottom, but over half of the sand sites had rock outcroppings. Seagrasses comprised 16% of the available habitat, green macroalgae comprised 12%, live bottom and red macroalgae each comprised 7%, and the Corrigan Reef oyster bars comprised < 2%. Six of the turtles utilized unvegetated sand and rock bottom surrounding Corrigan Reef (65 - 78% of foraging ranges and 64 - 82% of locations), and three turtles utilized the vegetated southern region (37 - 64% of foraging ranges and 31 - 57% of locations). Compositional analyses indicated that turtles used rock outcroppings in their foraging ranges at a significantly higher proportion than available within the study area. Additionally, live bottom and green macroalgae were utilized significantly more than seagrasses. Water depth ranged from intertidal oyster reefs to depths > 3 m, but turtles preferred 1-3 m depths within their foraging ranges. Daily activities of turtles were attributed to food acquisition and bioenergetics, while their habitat associations may be correlated to habitat structure, prey availability, competition, and developmental stage. ( ,, )
Subject:
Kemp's ridley turtle, telemetry, activity patterns, habitat preference
Thesis:
Thesis (Ph. D.)--University of Florida, 2000.
Bibliography:
Includes bibliographical references (leaves 144-163).
Additional Physical Form:
Also available on the World Wide Web; PDF reader required.
General Note:
Printout.
General Note:
Vita.
Statement of Responsibility:
by Jeffrey R. Schmid.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
45840299 ( OCLC )
002566154 ( AlephBibNum )
AMT2435 ( NOTIS )

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ACTIVITY PATTERNS AND HABITAT ASSOCIATIONS
OF KEMP'S RIDLEY TURTLES, Lepidochelys kempi,
IN THE COASTAL WATERS OF THE CEDAR KEYS, FLORIDA












By

JEFFREY R. SCHMID


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


2000















ACKNOWLEDGMENTS

I am indebted to Drs. Alan B. Bolten and Karen A. Bjorndal for their

guidance and patience in my quest to solve some of the riddles of the Cedar Key

ridleys. Drs. Franklin Percival, William Lindberg, and Paul Zwick provided me

with valuable suggestions concerning my research efforts. I thank all these

committee members for their advice and support during my studies and research.

I thank Drs. Ed Standora and Steve Morreale for their instructions in the

art of marine turtle telemetry and providing me with many of their trade secrets;

Dr. Ashish Mehta for his assistance with developing the protocol and procuring

the equipment for benthic sampling; and Drs. Joseph Davis and Frank Maturo for

their assistance in identifying macroalgae and invertebrate species, respectively.

Jamie Barichivich, Mike Cherkiss, and Tracey Collins proved themselves

exemplary field assistants, withstanding the monotonous hours at the radio

receiver, the deprivation of sleep, and the frenzied retreats from approaching

thunderstorms. I thank Monica Bando, Manjula Tiwari, and Dan Wood for

volunteering some of their time during data collection. I also thank Lisa Gregory

for her assistance and good cheer during these laborious times.

Special thanks to Edgar and Rosa Campbell for allowing unrestrained use

of their facilities and treating me as a member of their family; Mac Bishop for

helping to keep the research vessel running; and Tracey Collins who also









assisted in my efforts to collect benthic samples and piloted an alternate vessel

when the other finally ceased to function.

The research reported in this dissertation would not have been possible

without the support of Larry H. Ogren, who provided this former dockhand the

opportunities necessary to complete such a venture, and Wayne N. Witzell, who

took me under his wing and safeguarded my efforts during federal budget cuts.

Funding for this project was provided by the National Marine Fisheries Service

(NMFS) Panama City and Miami Laboratories and NMFS grants to the Archie

Carr Center for Sea Turtle Research.

Finally, I am grateful to my mother, Susan R. Schmid, my father, John J.

Schmid, and my brother, Thomas S. Schmid, for their moral support and

encouragement throughout my educational endeavors, and my girlfriend, Jill L.

Ryder, for her love and endurance during preparation of this manuscript.















TABLE OF CONTENTS

page

A C K N O W LE D G M E N T S ......................................... ........................ ................. ii

LIST O F TA B LE S ...........................................................................................vii

LIS T O F F IG U R E S ............................................................................................. x

A B S T R A C T .........................................................................................................x ii

CHAPTERS

1 KEMP'S RIDLEY TURTLE CONSERVATION AND RESEARCH................1

C conservation H history .................................................................................. 1
R research Efforts ......................................................................................... 4
T agg ing S tud ies .................................................................................... 8
Telem etry Studies ............................................................................... 16
Habitat Characterization...................................................................... 21
Research O objectives ................................................................................ 23

2 ACTIVITY PATTERNS OF KEMP'S RIDLEY TURTLES............................26

Predictions and Hypotheses..................................................................... 30
M materials and M ethods ............................................................................. 33
D ata C collection .................................................................................... 33
D ata A na lysis ...................................................................................... 38
R results ....................................................................................................... 45
Equipm ent Perform ance ..................................................................... 45
Telem etry O verview ............................................................................ 46
S ite F id e lity .......................................................................................... 4 9
T idal O orientation .................................................................................. 50
Rate of M ovem ent............................................................................... 58
Respiratory Behavior........................................................................... 66
D discussion ......................................................................................... .. 75

3 HABITAT ASSOCIATIONS OF KEMP'S RIDLEY TURTLES..................... 90

Predictions and Hypotheses..................................................................... 95
Materials and Methods .............. .......................... 96









D ata C collection ................................................................................... 96
D ata A analysis ................................................................................ 101
R results .............................................................................. .. ................. 106
Habitat Availability........ .... ........... .................. 106
Habitat Utilization ......... .... ............. .................. 111
Habitat Preference ......... ... ........... .................. 111
Depth Preference............. ............. .................. 117
D discussion .......................................................................................... 123
Management Implications........ ......... .................. 135

4 S U M M A R Y ......................................................................................... 138

A activity Patterns .................................................................................. 138
H habitat A analyses ................................................................................. 141

LITERATU R E C ITED ................................................................................. 144

APPENDICES

A PERCENT HABITAT COMPOSITIONS FOR COMBINATIONS OF
BENTHIC SUBSTRATES AND INDIVIDUAL BIOLOGICAL
ASSEMBLAGES............. ............. .................. 164

Prim ary Substrates ............................................................................. 164
Substrates with Rock........ .... ............. .................. 165
Sand w ith R ock ................................................................................... 166
S eagrass ....................................................................... ...................... 167
G reen A lgae ....................................................................................... 168
R ed A lgae ........................................................................................... 169
Live B bottom ........................................................................................ 170

B PERCENT HABITAT COMPOSITIONS FOR BENTHIC
SUBSTRATES AND PAIRED BIOLOGICAL ASSEMBLAGES .........171

Seagrass-Green Algae............ ......... .................. 171
Seagrass-Red Algae ............ ............. .................. 172
Seagrass-Live Bottom ......... ... ........... .................. 173
Green Algae-Red Algae ........................................ 174
Green Algae-Live Bottom ............ ....... .................. 175
Red Algae-Live Bottom............ ......... .................. 176

C PERCENT HABITAT COMPOSITIONS FOR BENTHIC
SUBSTRATES AND TERTIARY COMBINATIONS OF
BIOLOGICAL ASSEMBLAGES AND ALL ASSEMBLAGES
COMBINED ................................ .................. 177









Seagrass-Green Algae-Red Algae ....... ... .................................... 177
Seagrass-Green Algae-Live Bottom ....... ... .................................... 178
Seagrass-Red Algae-Live Bottom ....... ... ..................................... 179
Green Algae-Red Algae-Live Bottom ............................ 180
All Biological Assemblages................. .......................... 181

D PERCENT HABITAT COMPOSITIONS FOR DEPTH INTERVALS......... 182

BIOG RAPHICAL SKETCH ....... ......... ........... ..................... 184









































vi















LIST OF TABLES


Table page

1-1 Mean annual growth rates and estimated values of
asymptotic length and intrinsic growth rate from the von
Bertalanffy growth interval equation for Kemp's ridley
turtles captured in Florida.................................. ............... 15

1-2 Mean surface and submergence durations for non-nesting
Kemp's ridley turtles in U.S. coastal waters. Brackets
indicate extrapolated values.............................. ............... 20

2-1 Summary of Kemp's ridley turtles monitored by radio and
sonic telemetry at the Cedar Keys, Florida....................... 47

2-2 Indices of serial correlation for determining the time to
independence of Kemp's ridley turtle locational data.
significant autocorrelation, ns no significant
autocorre lation................................................. . . ......... 48

2-3 Mean bearings and vector lengths for telemetered Kemp's
ridley turtles during falling and incoming tides................... 56

2-4 Mean rate of movement and percent compositions of
movement rates for Kemp's ridley turtles. Standard
deviations are given in parentheses. Means that share
the same superscript are not significantly different using
the nonparametric multiple comparison procedure.............. 62

2-5 Mean rate of movement for telemetered Kemp's ridley
turtles by time of day. A > symbol indicates a significant
difference between time intervals using the Kruskal-
Wallis test for two levels and the nonparametric multiple
comparison procedure for four levels. ................ 64









2-6 Mean rate of movement for Kemp's ridley turtles and tidal
speeds by tide state. A < symbol indicates a significant
difference between tidal states using the Kruskal-Wallis
te s t ..................................................... ............... . . .......... 6 5

2-7 Summary of the surface and submergence durations for
telemetered Kemp's ridley turtles. Standard deviations
are given in parentheses. Means that share the same
superscript are not significantly different using the
nonparametric multiple comparison procedure.................... 67

2-8 Mean surface durations of Kemp's ridley turtles by time of
day. A > symbol indicates a significant difference
between time intervals using the Kruskal-Wallis test for
two levels and the nonparametric multiple comparison
procedure for four levels. Parentheses were used to
consolidate significant differences.................... .............. 70

2-9 Mean submergence durations of Kemp's ridley turtles by
time of day. A > symbol indicates a significant difference
between time intervals using the Kruskal-Wallis test for
two levels and the nonparametric multiple comparison
procedure for four levels. Parentheses were used to
consolidate significant differences................... .............. 71

2-10 Spearman correlation analyses of rate of movement,
number of surfacings per hour, and mean hourly surface
and submergence durations for Kemp's ridley turtles.
Number of surfacings and surface/submergence
durations were pooled within the time intervals of
consecutive locations. P-values are in parentheses and
significant correlations are in bold..................... ............... 73

2-11 Published sources of surface and submergence durations
for Kemp's ridley turtles. Brackets indicate extrapolated
v a lu e s ................................................ ................ .. . ......... 8 0

2-12 Summary of home range analyses for subadult marine turtles
inhabiting summer foraging grounds. CM = Chelonia
mydas, CC = Caretta caretta, El = Eretmochelys
imbricata, and LK = Lepidochelys kempi................................ 88

3-1 Summary of Kemp's ridley turtles used in habitat analyses at
the Cedar Keys, Florida...... ..................... .................. 102









3-2 Percent composition of primary substrates for the biological
assemblages and their species components.................. 109

3-3 Compositional analyses of Kemp's ridley turtle habitat
preference for combinations of benthic substrates and
individual biological assemblages. See Appendix A for
the habitat compositions of each dataset......................... 113

3-4 Compositional analyses of Kemp's ridley turtle habitat
preference for benthic substrates and paired biological
assemblages. See Appendix B for the habitat
com positions of each dataset...................... .............. 115

3-5 Compositional analyses of Kemp's ridley turtle habitat
preference for benthic substrates and tertiary
combinations of biological assemblages and all
assemblages combined. See Appendix C for the habitat
com positions of each dataset........................... .............. 116

3-6 Percent composition of benthic substrates and biological
assem blages at 0.5 m depth intervals................................ 119















LIST OF FIGURES


Figure page

1-1 Historical records of the annual number of Kemp's ridley
turtle nests at Rancho Nuevo, Mexico................. ............... 5

1-2 Surface circulation and hypothetical dispersal paths of
epipelagic Kemp's ridley turtles in the Gulf of Mexico ........... 7

1-3 Size class compositions for Kemp's ridley turtles in western
Apalachee Bay, Cedar Keys, Withlacoochee and Crystal
Rivers, Chesapeake Bay, Georgia/South Carolina
waters, and Cape Canaveral............................. ............... 10

2-1 Map of west-central Florida showing the Cedar Keys study
area ................................... ...................... ............ 34

2-2 Map of the tracking area for Kemp's ridley turtles and the
Cedar Keys archipelago. Squares and triangles
represent channel m arkers................................ ............... 37

2-3 Locations and home ranges of Kemp's ridley turtles relative
to Corrigan Reef. Squares and triangles represent
channel markers and stars denote the release site of
each turtle. Numbers indicate the total area of the home
range .................................................................. .............. 51

2-4 Home range area versus number of locations for Kemp's
rid ley tu rtle s ....................................................... . . ......... 54

2-5 Mean bearings and vector lengths by tide state for Kemp's
ridley turtles. Black arrows indicate the mean of mean
bearings and vector lengths for turtles and white arrows
indicate mean tidal bearings for 1995............................... 57

2-6 Hourly bearings and distances traveled by tide state for
individual Kemp's ridley turtles. Black arrows indicate the
mean bearings for turtles and white arrows indicate
m ean tidal bearings for 1995............................. ............... 59









2-7 Frequency distribution of surface durations for Kemp's ridley
turtles. Numbers indicate total number of surfacings .......... 68

2-8 Relationship of home range area and mass for subadult
marine turtles tracked via radio and sonic telemetry.
Open squares from van Dam and Diez (1998), open
diamonds from Mendonga (1983) and Ehrhart (1980),
filled diamonds from Renaud et al. (1995), open circles
from present study, open triangle from Byles (1988),
and filled triangle from Epperly et al. (1995)........................ 86

3-1 Map of west-central Florida showing the study area for
Kemp's ridley turtle habitat analyses.............................. 97

3-2 Habitat maps of primary benthic substrates and substrates
with rock within the study area.................. .................. 107

3-3 Habitat maps of seagrasses, green algae, red algae, and
live bottom w within the study area................... .............. 110

3-4 Mean compositions of benthic substrates and biological
assemblages utilized by Kemp's ridley turtles................. 112

3-5 Bathymetric map of the study area. Squares and triangles
represent channel markers and star denotes the location
of the tide station................ ............... 118

3-6 Frequency distribution of depth at the locations and in the
home ranges of Kemp's ridley turtles. Means and
standard deviations accompany the legend of each
fig u re ................................................ ................ . . ......... 12 0


3-7 Life history model of Kemp's ridley turtle habitat utilization......... 129















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

ACTIVITY PATTERNS AND HABITAT ASSOCIATIONS
OF KEMP'S RIDLEY TURTLES, Lepidochelys kempi,
IN THE COASTAL WATERS OF THE CEDAR KEYS, FLORIDA

By

Jeffrey R. Schmid

May 2000

Chairman: H. Franklin Percival
Major Department: Wildlife Ecology and Conservation

Radio and sonic telemetry were used to investigate the site fidelity, tidal

orientation, rate of movement (ROM), respiratory behavior, and habitat

associations of Kemp's ridley turtles, Lepidochelys kempi. Nine turtles were

tracked east of the Cedar Keys, Florida, for up to 70 days after release and

occupied 5 30 km2 foraging ranges. The mean of mean turtle bearings on

incoming (48490) and falling (232410) tides were significantly oriented to the

mean directions of tidal flow (3790, p<0.0025, and 23490, p<0.005,

respectively). Turtles had a mean ROM of 0.440.33 km/hr (range: 0.004 1.758

km/hr), a mean surface duration of 1815 seconds (range: 1 88 seconds), and

a mean submergence duration of 8.46.4 minutes (range: 0.2 60.0 minutes).

ROM was negatively correlated with surface and submergence durations and










positively correlated with the number of surfacings. Furthermore, ROMs were

higher and surface and submergence durations were shorter during the day.

Habitat associations of Kemp's ridley turtles were analyzed in terms of

availability, utilization, and preference using compositional analyses. Forty-eight

percent of the study area consisted of sand bottom, but over half of the sand

sites had rock outcroppings. Seagrasses comprised 16% of the available habitat,

green macroalgae comprised 12%, live bottom and red macroalgae each

comprised 7%, and the Corrigan Reef oyster bars comprised < 2%. Six of the

turtles utilized unvegetated sand and rock bottom surrounding Corrigan Reef

(65 78% of foraging ranges and 64 82% of locations), and three turtles utilized

the vegetated southern region (37 64% of foraging ranges and 31 57% of

locations). Compositional analyses indicated that turtles used rock outcroppings

in their foraging ranges at a significantly higher proportion than available within

the study area. Additionally, live bottom and green macroalgae were utilized

significantly more than seagrasses. Water depth ranged from intertidal oyster

reefs to depths > 3 m, but turtles preferred 1-3 m depths within their foraging

ranges. Daily activities of turtles were attributed to food acquisition and

bioenergetics, while their habitat associations may be correlated to habitat

structure, prey availability, competition, and developmental stage.















CHAPTER 1
KEMP'S RIDLEY TURTLE CONSERVATION AND RESEARCH



Conservation History

The Kemp's ridley turtle, Lepidochelys kempi, is the most endangered

species of marine turtle (Ross et al., 1989; Magnuson et al., 1990). Human

impacts on the various life history stages of the Kemp's ridley turtle have resulted

in their rapid decline in numbers. Exploitation of eggs (Hildebrand, 1982),

slaughter of nesting females (Pritchard, 1969), commercial fisheries for subadults

and adults (Pritchard and Marquez, 1973; Marquez, 1994), and incidental

capture of subadults and adults in shrimp trawls (Ross et al., 1989; Magnuson et

al., 1990) have been identified as causes for the population decline. Initial efforts

to conserve this species concentrated on protecting the primary rookery at

Rancho Nuevo, Tamaulipas, Mexico, where almost the entire population of adult

female Kemp's ridley turtles come ashore to nest (Marquez, 1994). During recent

years, efforts have focused on reducing the capture of Kemp's ridley turtles in the

U.S. and Mexican shrimp fisheries.

Prior to 1961, the location of Kemp's ridley rookeries was unknown until a

documentary film made in 1947 was discovered by marine turtle biologists (Carr,

1963; Hildebrand, 1963). In this film, an estimated 40,000 females nested during

the daylight hours in a single nesting aggregation known as an arribada (Spanish









for "arrival"). By 1966, when the Mexican government established the first

protection camp at Rancho Nuevo, these arribadas only reached 2,000 turtles

(Marquez, 1994). This rapid decrease in numbers was attributed to decades of

heavy human exploitation of adult females and their eggs, coupled with the

natural predation at the nesting beach, which resulted in virtually no recruitment

to the aging adult population. Protection of the nesting beach by Mexican

authorities essentially halted the exploitation of the females and their nests. The

U.S. government listed the Kemp's ridley turtle as endangered in 1970 and

federal protection of the species was initiated under the Endangered Species Act

of 1973 and subsequent amendments (Magnuson et al., 1990).

Since 1978, Mexican and U.S. authorities have participated in a

cooperative program for Kemp's ridley research and conservation. During each

nesting season, biologists from both countries patrol the beaches of Rancho

Nuevo, measure and tag nesting females, and relocate eggs to protected corrals.

The hatchery program has been closely monitored and has resulted in the

release of approximately 20,000 hatchlings annually from 1966-78 and 50,000

thereafter (Marquez, 1994). The number of nesting females provides the best

available index for the size of the Kemp's ridley population (Magnuson et al.,

1990) and has been calculated from the total number of nests divided by the

average number of nests deposited by females each year. This population

parameter is particularly sensitive to the annual number of clutches laid by

females, and estimates have ranged from 1.5 to 3 nests/female/season (Rostal

et al., 1997). Therefore, the total number of nests observed at Rancho Nuevo









has been the standard used to assess the status of the species (U.S. Fish and

Wildlife Service and National Marine Fisheries Service, 1992).

Despite intensive protection of the nesting beach, the reproductive output

of the population steadily declined from a total of 954 nests in 1979 to a low of

702 nests in 1985 (U.S. Fish and Wildlife Service and National Marine Fisheries

Service, 1992). Incidental capture of subadult and adult turtles in commercial

fisheries, particularly shrimp trawling, was identified as the major source of

mortality hindering the restoration of the species (Ross et al., 1989; Magnuson et

al., 1990). In 1987, regulations were enacted requiring the seasonal use of turtle

excluder devices (TEDs) in shrimp trawlers operating in the offshore waters from

North Carolina to Texas. By 1994, legislation was passed requiring year-round

use of TEDs in all shrimp trawlers operating in U.S. waters. In addition, the

Mexican government announced in 1993 that offshore shrimp trawlers operating

in the Gulf of Mexico and Caribbean Sea would be required to use TEDs.

There are indications that the binational conservation efforts of the past

three decades may be benefiting the highly endangered Kemp's ridley turtle. The

number of nests recorded at Rancho Nuevo has been steadily increasing since

the mid-1980's. Newly established camps to the north and south of Rancho

Nuevo are also reporting increases in nest numbers (Marquez et al., 1996). In

1998, researchers recorded 2,409 nests at Rancho Nuevo, which was the

highest observed level of nesting in 27 years (Marquez et al., 1999). Protection of

the nesting beach has presumably led to increased numbers of subadult turtles in

U.S. coastal waters, but there are no quantitative data to substantiate this









supposition (Ogren, 1989; Ross et al., 1990; Schmid, 1998). Increased nesting

may be attributable to the reduced mortality of adults and subadults resulting

from the restrictions placed on the shrimp fishery (Turtle Expert Working Group,

1998; Marquez et al., 1999). Nevertheless, the status of the Kemp's ridley turtle

remains precarious as nesting intensity is still drastically reduced when the

baseline is shifted to historical levels (Fig. 1-1). Furthermore, human

encroachment in critical habitats, such as the nesting beach and coastal foraging

grounds, continues to threaten the recovery of this species.



Research Efforts

As with the conservation efforts, much of the research conducted on

Kemp's ridley turtles has focused on the reproductively active females. Tagging

studies have indicated that female Kemp's ridley turtles leave the Mexican

nesting beach and migrate northward to feeding grounds offshore of Louisiana or

southward off of Campeche (Pritchard and Marquez, 1973). Satellite telemetry

has demonstrated that the females typically travel in continental shelf waters less

than 50 m deep (Byles, 1989; Byles and Plotkin, 1994). Virtually nothing is known

about adult male Kemp's ridley turtles other than their occurrence off the nesting

beach during mating (Ross et al., 1990).

A number of authors have proposed dispersal scenarios for hatchling

Kemp's ridley turtles once they have left the Rancho Nuevo nesting beach

(Pritchard and Marquez, 1973; Carr, 1980; Collard, 1990; Collard and Ogren,

1990), but there is little information concerning their actual pelagic development.













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Collard and Ogren (1990) hypothesized that post-hatchling Kemp's ridleys

become entrained within the Mexican Current and are then transported to the

Loop Current or a Loop Current eddy via an eastward flowing jet in the

northwestern Gulf of Mexico (Fig. 1-2). Wind-driven surface currents west of the

Mississippi River or Loop Current eddies to the east may eject turtles into the

coastal waters of the northern Gulf. Kemp's ridley turtles embedded within the

Loop Current are transported out of the Gulf through the Straits of Florida and

then carried northward by the Florida Current/Gulf Stream. Individuals in the

western edge of the Florida Current/Gulf Stream may enter the coastal waters of

New England either by actively swimming shoreward or by passive transport in

meanders or warm-core eddies of the Gulf Stream (Carr, 1980; Collard and

Ogren, 1990). Some turtles remain within the Gulf Stream where they are

transported across the North Atlantic Ocean to the coasts of the Azores and

Europe (Pritchard and Marquez, 1973; Carr, 1980; Brongersma, 1982; Bolten

and Martins, 1990; Marquez, 1994). There has been considerable debate as to

whether these individuals are able to survive in the North Atlantic Gyre and

recruit to the Gulf of Mexico breeding population (Carr, 1980; Ogren, 1989;

Collard and Ogren, 1990).

Post-pelagic Kemp's ridley turtles (20 25 cm straight-line carapace length

[SCL]) recruit to inshore waters from Texas to Massachusetts and begin a

coastal-benthic stage of development. The smallest turtles in U.S. waters have

been found in New England and this observation supports the hypothesis that

pelagic juveniles are transported out of the Gulf of Mexico, travel northward with













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the Florida Current/Gulf Stream, and then shoreward to the northeastern

seaboard (Carr, 1980; Ogren, 1989). The smallest post-pelagic turtles in the Gulf

of Mexico are found in the coastal waters of the Texas-Louisiana border and the

Florida panhandle east of Cape San Bias (Ogren, 1989). Collard and Ogren

(1990) suggested that these two areas were ejection points for juvenile turtles

that have completed their pelagic development within the Gulf. In-water research

methods are necessary to investigate the Kemp's ridley turtles that occur in the

estuarine systems along the Atlantic and northern Gulf coasts. The remainder of

this chapter will focus on the tagging and telemetric studies that have been used

to characterize the aggregations of wild, subadult turtles in U.S. coastal waters.



Tagging Studies

In 1955, Carr and Caldwell (1956) conducted tagging experiments with

Kemp's ridley turtles captured in the former turtle fishery of west Florida and

provided the first scientific data for this species. Further investigations of Kemp's

ridley turtles in U.S. coastal waters were not initiated until after their listing in the

Endangered Species Act of 1973. Since then, long-term tagging studies have

characterized the size classes, seasonal occurrence, long-distance migrations,

local movements, and growth of subadult turtles in the northwestern Atlantic

Ocean and the northern Gulf of Mexico.









Size classes

Ogren (1989) described the life history of the Kemp's ridley turtle as a

juvenile epipelagic stage (< 20 cm SCL), a coastal-benthic subadult stage (20-60

cm SCL), and a coastal-benthic adult stage (> 60 cm SCL). Carr (1980) and

Ogren (1989) suggested an increasing north-south size gradient for subadult

turtles along the U.S. Atlantic coast. Smaller turtles are typically captured in New

England (2 = 30 cm SCL in New York waters; Standora et al., 1992), but an

increasing gradient in mean size or size class composition is not observed when

comparing collections of Kemp's ridley turtles from Virginia, South

Carolina/Georgia, and Florida (Fig. 1-3). All the aggregations were primarily

composed of early to mid-subadults (20-40 cm SCL) with the exception of a few

adult-size turtles captured in east-central Florida. However, these distributions

and measures of central tendency are subject to error owing to small sample

sizes and sampling bias. The comparison is further complicated by the fact that

individuals move among these areas seasonally (see following section).

A clinal size pattern has not been observed for Kemp's ridley turtles in the

northern Gulf of Mexico (Ogren, 1989), although there were indications that

larger turtles occur in deeper water offshore (Rudloe et al., 1991). A comparison

of the mean sizes and size class compositions from northwestern and west-

central Florida does suggest an increasing north-south size gradient in the

eastern Gulf (Fig. 1-3). Sixty-six percent of the turtles captured in the Florida

panhandle were early to mid-subadults (Rudloe et al., 1991), compared to 24% in

the Cedar Keys (Schmid, 1998). However, this observation may be the result of



















































































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gear bias as the former study was based on turtles captured in commercial

fisheries, primarily shrimp trawls, and the latter was based on fishery-

independent captures with entanglement nets. Large-mesh tangle nets are

known to favor the capture of larger turtles (Carr and Caldwell, 1956; Schmid and

Ogren, 1992).

A temporal difference has been noted in size distributions of Kemp's ridley

turtles in west-central Florida (Schmid, 1998). All but one of the turtles examined

by Carr and Caldwell in the mid-1950s were greater than 40 cm and 8% of the

specimens were greater than 60 cm SCL (Fig. 1-3). By comparison, 24% of the

turtles captured from 1986 to 1995 were 20-40 cm SCL and 76% were 40-60 cm

SCL. Gear bias was ruled out as both studies utilized large-mesh tangle nets.

The observed difference could be indicative of a demographic shift which has

resulted from the protection of the nesting beach over the past three decades

(Schmid, 1998). However, Carr and Caldwell relied upon captures from the

commercial fishery and larger turtles may have been preferentially landed given

their higher market value. Interestingly, some Cedar Keys turtle fishermen

referred to smaller turtles as "housekeepers" which were customarily released to

"tend the house" of the larger turtles (Schmid, pers. obs.). This anecdote may

explain the lack of smaller size classes in the turtle fishery and suggests the

fishermen may have been practicing the first conservation efforts for this species.



Seasonal occurrence and migrations

Subadult Kemp's ridley turtles are captured as far north as Cape Cod Bay,

and occur in Long Island Sound (Morreale and Standora, 1998) and Chesapeake









Bay (Musick and Limpus, 1997) between June and November. Increasing

numbers of turtles are captured off Cape Canaveral from January to March

(Henwood and Ogren, 1987; Schmid, 1995). The results of tagging studies along

the Atlantic coast indicate a seasonal north-south migration of subadult Kemp's

ridley turtles. Turtles tagged off the Florida east coast during the winter have

been recaptured in northeastern waters during the summer, and turtles tagged in

northeastern waters in summer have been recaptured off Florida in winter

(Henwood and Ogren, 1987; Schmid, 1995). In recent years, Kemp's ridley

turtles tagged on the east coast have been observed nesting at Rancho Nuevo

(Schmid, 1995; Schmid and Witzell, 1997; Witzell, 1998), providing support that

subadult turtles in the Atlantic recruit to the Gulf of Mexico breeding population.

Kemp's ridley turtles are captured in the nearshore waters of the

northeastern Gulf of Mexico from April to November (Carr and Caldwell, 1956;

Schmid and Ogren, 1990, 1992; Schmid, 1998). Ogren (1989) proposed an

offshore migration based upon the capture of turtles in deeper waters during the

winter (Rudloe et al., 1991). Tag-recapture data along the northern Gulf coast

have demonstrated east-west movements of subadult Kemp's ridley turtles (Carr,

1980; Ogren, 1989). However, there are no recoveries that indicate a seasonal

migration in the eastern Gulf (Schmid, 1998). Turtles in the northern Gulf may be

moving to warmer waters offshore or may travel southward as has been

demonstrated for their Atlantic conspecifics.









Local movements

Kemp's ridley turtles have been recaptured at sites of initial capture within

a relatively short period, indicating fidelity to specific areas during their seasonal

occurrence in coastal waters. Carr and Caldwell (1956) noted that a turtle

released in the Cedar Keys traveled approximately 35 km to the original capture

site at the Withlacoochee-Crystal River fishing grounds within 43 days. Short-

term fidelity to capture sites has also been observed along the eastern seaboard

in Long Island Sound (Morreale and Standora, 1998), Chesapeake Bay (Musick

and Limpus, 1997), and Cape Canaveral (Schmid, 1995). In addition to short-

term recaptures, long-term and multiannual recaptures of Kemp's ridley turtles in

the Cedar Keys indicate that turtles remigrate to capture sites and may do so for

at least 4 years (Schmid, 1998).



Growth

Marine turtle studies commonly report growth rates in terms of the annual

increase in the carapace length between initial capture and subsequent

recapture. Tagging studies of wild, subadult Kemp's ridley turtles have yielded

little information on growth owing to the lack of recapture data and the short

duration of recaptures that have been recorded. Extrapolating annual growth

rates from short-term recaptures will amplify errors associated with the carapace

measurements and will yield overestimates during periods of rapid growth.

Kemp's ridley turtles recaptured during their seasonal occurrence at the Cedar

Keys exhibited a significantly higher growth rate (7.73.6 cm/yr) than that for










turtles recaptured between seasons (3.31.1 cm/yr; Schmid, 1998). However, all

within-season recaptures were less than 180 days. Recaptures between seasons

were of longer duration and the growth rates for these turtles may be more

representative of the yearly increase in carapace length.

The removal of short-term recaptures increases the accuracy of annual

growth rate estimates (Table 1-1), but also decreases the sample size. Growth

rates of 6 9 cm/yr were calculated for Kemp's ridley turtles captured in Cape

Canaveral (Table 1-1). However, all but one of the turtles in this study were

recaptured in less than a year. Growth rates of 4 5 cm/yr were calculated for

turtles collected at the Cedar Keys (Table 1-1). Approximately half of the

recaptures in this latter study were greater than one year duration, thus

decreasing extrapolation error. Furthermore, precision was increased as all

measurements were performed by a single person using the same equipment

(Bolten, 1999). A comparable growth rate of 4.0 cm/yr was reported from short-

term recaptures of Kemp's ridley turtles in New York waters (Morreale and

Standora, 1998).

Growth models have been applied to marine turtle mark-recapture data in

order to estimate population parameters such as the age of reproductive maturity

and the duration of life history stages. The Kemp's ridley turtle datasets from

Florida were fitted with the von Bertalanffy growth equation (Table 1-1), but the


















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resulting asymptotic lengths were either underestimated (Cape Canaveral) or

overestimated (Cedar Key) when compared to the mean length of nesting

Kemp's ridley turtles (64.2 cm converted SCL; Schmid and Witzell, 1997). Small

sample sizes with truncated distributions of lengths, combined with differences in

growth rates within and between these two areas, were identified as factors

affecting the growth model parameters. Consequently, the datasets were

combined and the growth equation for all recaptures was selected as the best fit

(Table 1-1). This growth equation estimated age to maturity at 8 9 years for the

smallest nesting female (56.0 cm converted SCL; Burchfield et al., 1988) and

10- 11 years for 60 cm SCL adult-size turtles (Ogren, 1989, Schmid, 1995,

1998). In addition, the estimated age of the smallest turtle (26.3 cm SCL, 2.6

years) and largest turtle (61.8 cm SCL; 11.0 years) in the combined dataset

suggested an 8 9 year duration for the coastal-benthic subadult stage (Schmid

and Witzell, 1997). However, the von Bertalanffy model assumes a steadily

decreasing growth rate during the succession of developmental stages and

recent evidence suggests ontogenetic variation in the growth rates of Kemp's

ridley turtles (Zug et al., 1997). Consequently, polyphasic growth models have

been proposed for this species (Chaloupka and Zug, 1997).



Telemetry Studies

Recoveries of tagged turtles reveal endpoints and periodicities of

migration, but yield little information on activities between capture and recapture

(Carr, 1980; Meylan, 1982). The introduction of radio (Baldwin et al., 1969),









ultrasonic (Ireland, 1980), and satellite (Timko and Kolz, 1982) telemetry

techniques to marine turtle studies increased our ability to investigate the free-

ranging behavior of turtles and thus fill the data gaps of mark-recapture studies.

Radio and sonic transmitters have been applied to subadult Kemp's ridley turtles

to investigate their short-term movements and activities, while satellite

transmitters have been used to document long-term migrations and activities.



Movements and migrations

The primary goal of the telemetric studies on Kemp's ridley turtles has

been to describe their movements and migrations. Subadult turtles tracked via

radio and sonic transmitters in Cape Cod Bay (Danton and Prescott, 1988) and

Chesapeake Bay (Byles, 1988) frequented shallow-water, seagrass shoals and

exhibited strong tenacity to specific areas. Byles (1988) also noted that Kemp's

ridley turtles did not appear to orient their movements with the direction of tidal

flow as was observed for loggerheads, Caretta caretta. Similar investigations in

New York waters have shown that Kemp's ridley turtles may reside near the point

of capture for up to 121 days (Morreale and Standora, 1998). Most of the

movements by turtles in this latter region were during the day (Standora et al.,

1989). Furthermore, turtles exhibited nondirected movements indicative of

foraging behavior from July to September when water temperatures were

> 150 C (Standora et al., 1990; Morreale and Standora, 1998). More directed

movements were observed in September and October when water temperatures

were < 150 C, and these eastward movements corresponded to departure from









coastal estuaries into the Atlantic Ocean. A southward migration during the fall

was indicated by two turtles that left the nearshore waters of Georgia in October

and traveled along the coast of northeastern Florida through November

(Gitschlag, 1996).

Satellite telemetry has been used to document the seasonal north-south

migration of Kemp's ridley turtles along the Atlantic seaboard. Subadult turtles

emigrate from New England waters in October and November and continue their

migration southward off the coasts of Virginia and North Carolina through

November (Standora et al., 1992; Morreale and Standora, 1998). Two separate

studies have documented overwintering in Florida and remigration northward the

following spring. A subadult turtle (< 60 cm SCL; Renaud, 1995) and an adult-

size turtle (60.7 cm; Gitschlag, 1996) traveled southward from the coastal waters

of Georgia and northern Florida in October and November, remained in coastal

waters south of Cape Canaveral from December through February, moved

northward in March and April, and resided off the South Carolina coast through

July. Satellite telemetry has also been used to document a west to east migration

in the Gulf of Mexico (Renaud, 1995). An adult-size turtle (60 cm SCL) held

captive for a year was released from south Texas in March, traveled across the

northern Gulf through August to waters offshore of west-central Florida, and was

last recorded north of Key West in December. The movements of this turtle

during the latter portion of the tracking interval indicate a possible southerly

migration for Kemp's ridley turtles in the eastern Gulf.









Behavior

Behavioral studies of Kemp's ridley turtles in U.S. coastal waters have

focused on patterns of respiratory durations, but it is difficult to compare the

results among studies owing to the different telemetric methodologies. The data

obtained from satellite transmitters are in terms of submergence patterns and are

summarized in 12-hour intervals, whereas the data obtained from radio

transmitters are in terms of surfacing patterns and are collected consecutively.

Nevertheless, some comparisons can be made between methodologies with

respect to submergence duration. Mean submergence durations recorded from

radio transmitters were generally less than those recorded via satellite and the

durations for backpack attachments were greater than tethered attachments for

both types of transmitters (Table 1-2). Standora et al. (1992) noted that a

backpack satellite transmitter would often indicate a turtle was diving when the

animal was a few centimeters below the surface and recommended tethered

transmitters for recording diving behavior. All telemetric studies have reported

relatively high percentages of time submerged for Kemp's ridley turtles except

Morreale and Standora (1998; Table 1-2). This latter study was conducted in

New England waters, where smaller turtles are known to occur, and the

variability in percent time submerged could be related to the transition between

developmental stages. New recruits from the pelagic stage may spend more time

at the surface than turtles that have already become established in the coastal-

benthic habitat.
























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Telemetric monitoring has demonstrated diel and seasonal shifts in the

surface and submergence durations of Kemp's ridley turtles, but there are no

distinct patterns among the few studies that have been conducted. Two radio-

telemetered turtles in Chesapeake Bay exhibited longer surface durations during

the day (Byles, 1988), although this observation was not tested statistically.

Another turtle tracked via radio along the southeast U.S. coast exhibited

significantly longer submergence durations at night (77.3 min) than during the

day (13.7 min; Gitschlag, 1996). Satellite telemetry has indicated that average

submergence durations of Kemp's ridley turtles were significantly higher during

the night for all seasons (n=2; Gitschlag, 1996) and average submergence

durations decreased in the spring (n=2; Gitschlag, 1996) and summer (n=4;

Renaud, 1995). The numbers of submergences were higher during the day for

both of these studies, but the seasonal patterns of submergence were opposite.

Furthermore, the mean numbers of submergences reported by Renaud were

approximately 7 times greater than those of Gitschlag. The differences between

studies employing the same methodology is probably due to the individual

variability among the few turtles tracked in each study. Intensive monitoring of a

larger number of animals is needed to investigate the behavior of Kemp's ridley

turtles.



Habitat Characterization

Characterizing the developmental habitats and determining the habitat

utilization of Kemp's ridley turtles have been identified as priorities in the









conservation and management of this species (Thompson et al., 1990; U.S. Fish

and Wildlife Service and National Marine Fisheries Service, 1992). Subadult

turtles typically inhabit coastal estuaries, and the biological and physical

attributes of the areas in which they are caught have been used to characterize

the habitats of this species. Carr (1942) first suggested that Kemp's ridley turtles

preferred the red mangrove (Rhizophora mangle) habitat based on the

observations of fishermen in southern Florida. Carr and Caldwell (1956) later

noted that this species was also captured on seagrass (Thalassia testudinum,

turtle grass, and Syringodium filiforme, manatee grass) shoals in the west-central

Florida turtle fishery. Ogren (1989) identified mud, sand, oyster shell, and turtle

grass as bottom types associated with the capture of subadult Kemp's ridley

turtles. No preference for bottom type was indicated except those corresponding

to portunid crab distribution (i.e. shallow seagrass beds and mud bottom bays of

coastal marshes). Rudloe et al. (1991) compared the substrates (mud, sand, and

seagrass) at the capture sites of subadult turtles in the northeastern Gulf of

Mexico and detected no significant preference for bottom type. Schmid (1998)

suggested that oyster reefs and mud bottom adjacent to the reefs were being

preferentially utilized by Kemp's ridley turtles in west-central Florida.

Information gathered on the daily movements of Kemp's ridley turtles can

also be used to characterize the habitat preferences of this species (Timko and

Kolz, 1982). Danton and Prescott (1988) observed that a telemetered subadult

turtle in Cape Cod Bay remained near a shallow-water shoal composed of

extensive eelgrass (Zostera marina) flats. Byles (1988) also noted utilization of









shoal areas by two telemetered Kemp's ridley turtles in Chesapeake Bay and

identified seagrass beds (Z. marina and Ruppia maritima) as the preferred

habitat within their foraging ranges. As noted previously for behavioral studies, a

larger number of turtles need to be tracked in order to characterize habitat

associations via telemetric methods.

All of the aforementioned studies have inferred habitat preferences by

Kemp's ridley turtles, but they are actually implying habitat utilization from the

observations at telemetry and capture locations (Thomas and Taylor, 1990).

There have been no efforts to quantify the amount of time Kemp's ridley turtles

spend utilizing their habitats, and none of the investigations to date have

characterized or quantified all of the habitat types available to turtles within the

respective study areas. Estimates of habitat availability and utilization are

commonly used to determine the habitat preferences of terrestrial animal

populations (White and Garrott, 1991) and such estimates should be used in

characterizing the foraging habitats of Kemp's ridley turtles (Schmid, 1994).



Research Objectives

Tagging studies have demonstrated that the coastal waters of west-central

Florida are an important developmental region for subadult Kemp's ridley turtles

(Schmid, 1998). Despite the long-term tagging efforts, there have been no

attempts to document the activities and behavior of Kemp's ridley turtles

inhabiting these foraging grounds. Radio and sonic telemetry have been used

extensively to analyze the local movements, site fidelity, and respiratory behavior









of Kemp's ridley turtles along the Atlantic coast. However, efforts to date have not

demonstrated patterns for these activities or preference for a particular habitat

type. The purpose of the present study is to investigate the activity patterns and

habitat associations of Kemp's ridley turtles in the nearshore waters of the Cedar

Keys. The objectives of this dissertation are as follows:

(1) To determine the extent to which Kemp's ridley turtles exhibit fidelity to

the Cedar Keys study area.

(2) To determine if the movements of Kemp's ridley turtles are oriented with

the direction of the prevailing tidal flow and if the rate of movement is

correlated to the rates of tidal flow.

(3) To determine if the rate of movement and respiratory activities of Kemp's

ridley turtles change with respect to time of day, and to determine if these

patterns are correlated with one another and body size.

(4) To characterize the various benthic habitats available within the Cedar

Keys study area.

(5) To estimate the utilization of habitat types by Kemp's ridley turtles.

(6) To determine if Kemp's ridley turtles are exhibiting habitat preference by

utilizing particular habitat types and water depths at a greater proportion

than available in the study area.

Chapter 2 provides an overview of the telemetric methodology used in the

present study and examines the daily activities of Kemp's ridley turtles as

outlined in objectives 1 3. Chapter 3 examines the association of Kemp's ridley

turtles with the coastal-benthic habitats of the Cedar Keys area as summarized in






25

objectives 4 6. Chapter 4 provides a synopsis of Chapters 2 and 3, and

presents recommendations for further research.














CHAPTER 2
ACTIVITY PATTERNS OF KEMP'S RIDLEY TURTLES


Knowledge of spatial patterns and movements is the first step in

comprehending the ecology of a species and is a vital component in the

conservation strategies for endangered wildlife populations (Weatherhead and

Hoysak, 1989). With the exception of migratory and nomadic movements, most

animals confine their activities to specific areas (Winter, 1977). These areas are

commonly referred to as "home ranges," though there has been considerable

debate concerning the interpretation of the home range concept and the methods

used to delineate the area (Harris et al., 1990; White and Garrott, 1990).

Regardless of the definition or methodology, a home range is a spatially and

temporally restricted area that an animal traverses while performing its normal

activities.

Estimating the size, shape, and patterns of movement within the home

range are important features in wildlife studies, particularly those concerned with

foraging behavior and habitat selection. McNab (1963) demonstrated that the

home range sizes of some mammalian species were strongly correlated with

their body sizes, foraging strategies, and relative food densities. Larger animals

expend more energy owing to their higher body mass, and, therefore, require a

greater area in which to acquire this energy. Furthermore, "hunters" (carnivores,

insectivores, frugivores, and granivores) utilize widely dispersed food resources









and tend to have larger home range sizes than "croppers" (herbivorous grazers

and browsers) of similar mass that utilize more densely distributed food.

Environmental conditions may also influence the body size and home range

relationship, though there are no clear trends (McNab, 1963).

Understanding patterns of animal movement requires information on the

environmental conditions in which movement occurs, as rhythmic patterns in the

natural environment are a major influence underlying the behavioral patterns of

animals (Nieuwolt, 1996). Each species adapts to diel and seasonal changes in

the physical factors of the environment, such as illumination and temperature,

and these adaptations are reflected in the activity patterns of the species

(Gourley, 1979). In vertebrate taxa, however, the biological advantages of

rhythmic activity are often determined by secondary ecological factors such as

predation and food acquisition (Cloudsley-Thompson, 1961).

Most studies of animal activity patterns have dealt with terrestrial species.

Radio telemetry is commonly employed to describe the movements and activities

of free-ranging animals, and these descriptions are then used to test for

correlations between the observed behaviors and environmental conditions

(White and Garrott, 1990). Since the advent of acoustical telemetry, behavioral

studies in the aquatic environment have focused on fish (Stasko and Pincock,

1977). Marine fish commonly exhibit daily activity patterns in response to

predictable changes in light and tidal cycles, and these patterns have adaptive

significance with respect to bioenergetics and niche definition (Colton and

Alevizon, 1983; Gruber et al., 1988; Nixon and Gruber, 1988). Similar activities









have been observed in marine turtles, but attention has focused on the seasonal,

rather than the daily, influences of the environment.

For example, the Kemp's ridley turtle, Lepidochelys kempi, is the most

endangered species of marine turtle and is distributed throughout the Gulf of

Mexico and northwestern Atlantic Ocean. Tagging studies have been conducted

in U.S. coastal waters to characterize regional aggregations of subadult turtles

and to investigate their movements and migrations. Recaptures along the Atlantic

coast have indicated a seasonal north-south migration. Turtles tagged off the

Florida east coast during the winter have been recaptured in northeastern waters

during the summer, and turtles tagged in northeastern waters in summer have

been recaptured off Florida in the winter (Henwood and Ogren, 1987; Schmid,

1995). Mark-recapture data along the northern Gulf coast have demonstrated

east-west movements (Carr, 1980; Ogren, 1989), but there are no recoveries that

indicate a seasonal migration. Short-term recaptures at sites of initial capture

have demonstrated fidelity to specific areas (Schmid, 1995; Musick and Limpus,

1997; Morreale and Standora, 1998), while long-term and multiannual recaptures

have indicated that some turtles remigrate to capture sites and may do so for at

least 4 years (Schmid, 1998). However, recoveries of tagged turtles only reveal

endpoints and periodicities of migration or movement, and yield little information

on their behavior between capture and recapture (Carr, 1980; Meylan, 1982).

Telemetric techniques have been used to investigate the activities of

Kemp's ridley turtles, and thus fill the data gaps of tagging studies, but the

primary goal of most studies has been to describe patterns of movement and









migration. Satellite transmitters have been used to document southward

migration from New England waters during the fall (Standora et al., 1992;

Morreale and Standora, 1998), overwintering off the east-central coast of Florida

and northward remigration in the spring (Renaud, 1995; Gitschlag, 1996), and

west-east migration in northern Gulf coastal waters (Renaud, 1995). Radio and

sonic transmitters have been applied to investigate tidal orientation in

Chesapeake Bay (Byles, 1988), diving patterns and seasonal movement patterns

in Long Island Sound (Standora et al., 1990; Morreale and Standora, 1998),

departure from inshore waters of New York during the fall (Standora et al., 1990;

Morreale and Standora, 1998), and southward movements along the east coast

of Florida during the winter (Gitschlag, 1996).

A few investigators have employed radio and sonic telemetry to describe

the localized movements and short-term site fidelity of Kemp's ridley turtles in

coastal estuaries (Byles, 1988; Danton and Prescott, 1988; Morreale and

Standora, 1998), but only Renaud and Williams (1997) have conducted home

range analyses for this species. Studies of Kemp's ridley behavior have focused

on seasonal and diel patterns of surface and submergence durations (Byles,

1988; Renaud, 1995; Gitschlag, 1996). However, these efforts have produced

insufficient and conflicting results owing to differences in the methodologies

employed, small numbers of turtles tracked in each study, and individual variation

by the few turtles tracked to date.

The eastern Gulf of Mexico, particularly the Cedar Key area of western

Florida, has been identified as an important developmental region for Kemp's









ridley turtles (Bjorndal and Bolten, 1990; Thompson et al., 1990; U.S. Fish and

Wildlife Service and National Marine Fisheries Service, 1992). However,

relatively little is known about the activities of turtles in this area other than

anecdotes from fishermen and observations from mark-recapture studies (Carr

and Caldwell, 1956; Schmid and Ogren, 1990, 1992; Schmid, 1998). Discerning

daily activity patterns and factors influencing these patterns would not only

benefit conservation and management efforts for this highly endangered species,

but would also provide insight into the ecological roles of Kemp's ridley turtles in

coastal habitats (Bjorndal and Bolten, 1990; Thompson et al., 1990). The

purpose of the present study is to provide information on the site fidelity,

movements, and respiratory behavior of Kemp's ridley turtles in the coastal

waters of the Cedar Keys, Florida, and to test hypotheses concerning tidal

orientation and diel patterns of movement and respiration.



Predictions and Hypotheses

1. Carr and Caldwell (1956) tagged and released Kemp's ridley and green

turtles (Chelonia mydas) obtained from Cedar Key fish houses, and noted that a

few turtles returned to the area where they had been originally captured within a

short period of time. The authors suggested that these turtles were exhibiting

homing behavior and were establishing home ranges during their seasonal

occurrence in the nearshore waters of western Florida. Kemp's ridley turtles

captured and tagged in the Cedar Keys have been recaptured at initial capture

sites both within and between seasons, prompting Schmid and Ogren (1990,









1992) to conclude that these turtles were seasonal residents with restricted home

ranges. I predict Kemp's ridley turtles will occupy well-defined foraging ranges in

the Cedar Keys study area and will exhibit fidelity to specific sites within the study

area.

2. Byles (1988) indicated that the movements of loggerhead turtles

(Caretta caretta) were strongly influenced by the tidal cycle, whereas Kemp's

ridley turtles did not range as far with the tide. However, my communications with

fishermen in the Cedar Keys and personal field observations in this area suggest

that Kemp's ridley turtles are moving with the prevailing tidal current. I will test the

null hypothesis that the direction of movement of Kemp's ridley turtles is

uniformly distributed during each tidal state. If turtles do exhibit significant tidal

orientation, I predict their rate of movement will increase with increasing tidal

velocity.

3. Most species of turtles are generally active during the day (diurnal),

though some also perform nighttime (nocturnal) activities such as nesting

(Cloudsley-Thompson, 1961; Gourley, 1979). Patterns of diurnal foraging and

nocturnal resting have been observed in subadult green (Mendonga, 1983) and

hawksbill turtles (Eretmochelys imbricata; van Dam and Diez, 1998), but these

patterns were not evident for subadult Kemp's ridley and loggerhead turtles

(Byles, 1988). Increased diurnal movements (Standora et al., 1989) and

increased crepuscular (sunrise and sunset) dive frequencies (Morreale and

Standora, 1998) have been suggested for Kemp's ridley turtles, but the authors

did not provide quantitative data to substantiate their inferences. I will test the null









hypothesis that the rate of movement and respiratory activities of Kemp's ridley

turtles are equally distributed throughout the 24-hour cycle.

4. Laboratory experiments have demonstrated an increase in respiratory

frequency from induced swimming in captive loggerhead (Lutz et al., 1989) and

green turtles (Butler et al., 1984; West et al., 1992). Resting turtles surfaced

intermittently to breathe, with one or more breaths per episode, followed by

longer submerged periods. Swimming turtles established a more continuous

pattern of surfacing to breathe. Regardless of the activity, there is a tendency for

the number of breaths per breathing episode to increase with submergence time

(Lutcavage and Lutz, 1997), therefore increasing the duration at the surface. I

predict the frequency of respiratory surfacings will increase, and the surface and

submergence durations will decrease, with increasing rate of movement in free-

ranging Kemp's ridley turtles.

5. The size of the home range areas of mammalian (McNab, 1963;

Gittleman and Harvey, 1982) and avian species (Schoener, 1968) have been

positively correlated with their body mass. This relationship has also been

demonstrated for green turtles foraging in a lagoonal habitat (Mendonga, 1983).

No such correlation has been demonstrated for Kemp's ridley turtles, but Ogren

(1989) suggested that smaller turtles are restricted to shallower water depths and

shorter dive durations owing to their higher metabolic rate and reduced lung

capacity. I predict that the home range area and respiratory durations of Kemp's

ridley turtles will increase with increasing carapace length and mass.









Materials and Methods



Data Collection



Study area

The study was conducted in Waccasassa Bay, which is located on the

west coast of Florida and east of the Cedar Keys (Fig. 2-1). The northern and

eastern boundaries of Waccasassa Bay are delineated by undeveloped

saltmarsh coastline. The Waccasassa River drains into the northeastern region

and is the major contributor of freshwater to this estuarine embayment (Wolfe,

1990). Research efforts were concentrated in the western portion of the bay,

which is bordered by the Cedar Keys archipelago and the fishing community of

Cedar Key. The southern region is open to the marine waters of the Gulf of

Mexico. The two prominent geographic features within Waccasassa Bay are

Corrigan Reef, a series of oyster and shell bars located in the northwestern

region, and Waccasassa Reefs, three parallel seagrass shoals in the eastern half

of the bay.



Capture of marine turtles

A large-mesh entanglement net (65 m length, 51 cm stretch mesh, and 20

meshes deep) was used to capture Kemp's ridley turtles near Corrigan Reef. The

net was set in areas of aggregation identified by Schmid (1998) and retrieved

upon capture of a turtle. Straight-line carapace length (SCL; nuchal notch to tip of




















































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postcentral scutes) was measured to the nearest 0.1 inch with forester's calipers,

and mass was measured to the nearest 0.25 Ibs with a spring scale.

Measurements were converted to metric for analyses owing to the measurement

scales of the available instruments. Turtles were tagged with an Inconel tag on

each fore flipper and a passive integrated transponder (PIT) tag was inserted in

the left front flipper. Turtles were held on board the tracking vessel for less than 5

hours prior to release.



Radio and sonic telemetry

Each turtle was instrumented with a CHP-87-L sonic transmitter

(Sonotronics, Tucson, AZ) and a MOD-050 radio transmitter with a TA-7

antenna (Telonics, Mesa, AZ). Sonic transmitters (32-44 kHz range with constant

or coded pulse interval) were attached to posterior marginal scutes. Stainless

steel wire was looped through the ends of the transmitter and plastic ties were

inserted through the loops and through holes drilled in the scutes. Sonic

transmitters were monitored with a N30A5B directional hydrophone and receiver

(Dukane Corp., St. Charles, IL). Buoyant radio transmitters (164-165 MHz band)

were attached to one of the postcentral marginal scutes by a 0.2 cm diameter

monofilament tether with a breakaway link (S. Morreale and E. Standora, pers.

comm.). Tether length was approximately two-thirds the carapace length of a

turtle, so that the tether would not tangle in the fore flippers and the turtle was

unable to bite the transmitter. Radio transmitter floats were constructed from SH

model Ecofoam (128 kg/m3; Deanco Inc., Winter Park, FL). Floats were painted









grey or black to decrease detection by predators (i.e., sharks) and coated with an

epoxy resin to reduce damage. Radio transmitters were monitored with a CE12

receiver (Custom Electronics of Urbana, Inc., Urbana, IL) connected to a

directional six-element Yagi antenna (Cushcraft Corp., Manchester, NH). The

radio antenna was mounted on a rotating mast approximately 3 m above the sea

surface.



Tracking protocol

Radio monitoring and sonic tracking were conducted from an 8.5 m

wooden hull vessel with an inboard engine. Telemetered turtles were released in

the area of capture, and tracking began after a 24-hour acclimation period.

Tracking was conducted opportunistically in 1994, and most data were collected

during the day. In 1995, turtles were systematically monitored for 4 tracking

intervals of approximately 12 hours each, so that observations were collected

each hour over two 24-hour cycles. At least 24 hours elapsed before initiating the

second tracking interval, at least 48 hours elapsed before initiating the third

interval, and at least 24 hours elapsed before initiating the fourth interval. After

the intensive tracking period, turtles were located opportunistically to establish

their presence in the study area. Intensive tracking efforts were abandoned if a

turtle traveled more than 6 km from South Bar Light located south of Corrigan

Reef (Fig. 2-2).

Radio telemetry was used to monitor surface times and durations (number

of pulses) of turtles and to obtain bearings for long distance tracking. Sonic














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telemetry was used to pinpoint the location of turtles and to track their

movements. Turtle locations were recorded hourly by homing-in on the sonic

signal and maneuvering the tracking vessel within 10 20 m of the turtle.

Distances were assessed by sighting a turtle and noting the strength of the sonic

signal at 1/2 gain on the receiver. Turtle locations were estimated from the

Universal Transverse Mercator (UTM) coordinates of the tracking vessel using a

Global Positioning System (GPS, NAV 5000DX with software upgraded to NAV

5000DLX, Magellan Systems Corp., San Dimas, CA) with differential correction.

Accuracy of the locational estimate was approximately 5 m as determined from

the variability associated with a fixed position. The tracking vessel was anchored

in the vicinity of a telemetered turtle between acquisition of locations. Direction of

tidal flow at each turtle location was determined by observation in 1994 and with

a handheld compass in 1995. Tidal flow rate was measured in 1995 by lowering

a weighted flowmeter (Serial #B, General Oceanics, Miami, FL) approximately 1

m below the surface and recording the number of revolutions per second within a

30-second period.



Data Analysis



Site fidelity

Site fidelity was determined from the tendency of animals to remain within

the Cedar Keys area and to maintain a stable home range size. The minimum

area method of home range estimation (Ackerman et al., 1990; White and









Garrott, 1990) was used to define the total area utilized by a telemetered turtle. A

convex polygon was constructed by connecting the outer locations so that the

internal angles of the polygon did not exceed 180 degrees. The computer

program HOME RANGE (Ackerman et al., 1990) was used to calculate the UTM

coordinates and area (km2) of each turtle's home range polygon and the

distances (m) traveled between consecutive locations.



Tidal orientation

Relative distances in the x (AX) and y (AY) directions were determined

between consecutive locations of each turtle

AX = x,+ x,
AY = y,+-y,


where xi is the north UTM coordinate and y1 is the east UTM coordinate for

location i. The angle (ad) in degrees between locations was calculated as


arctan(AY / AX)(1800/ i) if AX > 0
1800 + arctan(AY / AX)(1800/ ir) if AX < 0
a,
900 if AX = 0 andAY > 0
2700 if AX = 0 andAY < 0


Angles were converted to bearings (bd) with the formula


b, = 90 -a,


and 3600 was added if the resulting value was negative (left of true north).









Directional data for each turtle were pooled respective to the tidal phase

(incoming or falling) in which they occurred. Mean rectangular coordinates were

computed for the pooled tidal phases of each turtle


X =- ( cos a)
n
Y = ( sin a)
n


Length of the mean vector (r) is a measure of concentration for the sample of

angles and was calculated for the pooled tidal phases of each turtle






When r=-O, the mean angle (a) is undefined (no concentration or multimodal


angles), and when rO, a is determined by


arctan(Y / X)(180 0/)
180 + arctan(Y / X)(1800 / n)
a=
90
270


if X > 0
if X<0
if X = 0 andY > 0
if X = 0and Y < 0


Mean angles were converted to mean bearings (b) as described for individual

angles. Angular deviation (s) was calculated with the formula


s= 180 -2 In r











Rate of movement and tidal speeds

Rate of movement (ROM) in km/hr was calculated as



ROM = d 1000
60


where di is the distance in meters between two consecutive locations and ti is the

time in minutes between locations. Using the conversion chart on the flowmeter,

tidal speed (T) in km/hr was calculated as


T = 0.096(F)


where F is the measured flow rate in revolutions/second.



Respiratory behavior

The radio transmitters emit 50 pulses per minute or one pulse every 1.2

seconds. Surface duration was calculated by multiplying the recorded number of

pulses by 1.2 seconds. Submergence duration was estimated by the number of

minutes elapsed from the beginning of the previous radio contact minus the

corresponding surface duration. Rates of movement and surface/submergence

durations were pooled for all turtles, by year tracked, and for each turtle by time

of day (Eastern Standard Time) using the two level time intervals [0800-1959 h

(day) and 2000-0759 h (night)] of Renaud (1995) and four level time intervals

[0500-0859 h (dawn), 0900-1659 h (day), 1700-2059 h (dusk), and 2100-0459 h









(night)] of Renaud et al. (1995). Surface durations, submergence durations, and

number of surfacings were also pooled within the time intervals of consecutive

locations for correlation analyses.



Statistical methods

A basic assumption in most statistical analyses of animal movements is

the independence between successive locations collected during telemetric

monitoring. Locational data collected via telemetry are considered independent if

an animal's current position is not a function of its previous positions (Swihart and

Slade, 1985 a,b; White and Garrott, 1990). The time to independence has been

described as the time necessary for an animal to traverse its home range

(Swihart and Slade, 1985a) or a statistically significant part of its home range

(Ackerman et al., 1990). However, minimum time interval to statistical

independence can be long enough to eliminate information of biological

significance (Andersen and Rongstad, 1989; Reynolds and Laundre 1990;

McNay et al., 1994). The length of time necessary for statistically independent

data can produce inaccurate estimates of daily distances traveled and activity

patterns since these behaviors often require a short sample period (Reynolds

and Laundre, 1990). Data collection at short, systematic intervals are needed to

maximize the behavioral information available from telemetry studies, despite the

violation of the independence assumption (Reynolds and Laundre, 1990; McNay

et al., 1994). Therefore, hourly sampling intervals were selected in order to

quantify the behavioral trends of Kemp's ridley turtles foraging in the Cedar Keys









area, despite the possibility of autocorrelated data. Efforts were made to use

statistical analyses that did not require the assumption of independent

observations, but this was not always possible. The computer program HOME

RANGE (Ackerman et al., 1990) was used to calculate three indices of serial

(auto-) correlation: t2/r2 (Swihart and Slade, 1985a), T (psi; Swihart and Slade,

1985b), and y (gamma; Swihart and Slade, 1986). These indices were applied to

1, 2, 4, and 6 hour intervals between successive locations of each turtle in order

to determine the minimum time to independence.

Batschelet (1981) suggested combining descriptive circular statistics for

each individual to create a second-order sample of mutually independent data

pairs. The mean bearings and mean vector lengths of each turtle were combined

to create a second-order sample of polar coordinates for each tidal phase. The

number of first-order observations for each individual must be equal in order for

the second-order data pairs to have the same weight, although slight departures

will not severely affect results. Since the tidal orientation data have unequal

sample sizes, it was assumed that the data pairs for each turtle had equal

weights. The V test (Batschelet, 1981) was used to test whether the mean

bearings of the turtles were clustered around the bearings of the incoming and

falling tides. Tidal bearings collected during 1995 were used to calculate mean

bearings for the incoming tides and the falling tides.

Distributions of variables (rates of movement and surface and

submergence durations) were tested with the Shapiro-Wilk test for normality.

Homogeneity of variances was tested with the F-test for two level time intervals









and Bartlett's test for homogeneity for four level time intervals. The Kruskal-

Wallis analysis was used to test for differences in means of the variables in the

absence of normality and/or nonhomogeneity of variances. Statistical

significance was accepted at P < 0.05. When a significant difference between

four level time intervals was detected and parametric assumptions had been

violated, a nonparametric multiple comparison procedure described by Daniel

(1990) was used to determine which means differed at ax = 0.05. Although the

use of the rate of movement and surface-submergence data as the sample unit

to compare across animals is psuedoreplication (Otis and White, 1999), these

analyses were performed to describe individual variability and to compare results

with previous studies. Spearman correlation coefficient was used to determine

the correlations among rates of movement, mean hourly surface and

submergence durations, and number of surfacings per hour for all turtles

combined, by year tracked, and for each turtle. Spearman correlation coefficient

was also used to determine the correlations between the body size (carapace

length and mass) and the home range area, mean rate of movement, mean

number of surfacings, mean surface duration, and mean submergence duration

of each turtle.









Results



Equipment Performance

Adverse weather conditions were a major limitation to telemetric

monitoring. Radio transmitters had a range of approximately 8 km given the

height (3 m) of the receiving antenna above sea level. Interference with the

reception of radio signals included the GPS antenna, electrical engine noise,

lightning discharge, and unidentified radio transmissions. The range of the radio

signals was also a function of the height of the transmitter antenna above the

water's surface, which was affected by the buoyancy of the transmitter and the

sea state. Four detached radio transmitters (2 with broken tether swivels and 2

with disconnected breakaway links) were recovered within 5-24 days after

application. Transmitters recovered 2-3 weeks after attachment had become

fouled by barnacles and hydrozoa.

Sonic transmitters were detected at distances up tol km under good

conditions and less than 100 m under poor conditions. Recognizable factors

affecting reception of the sonic signal include sea state, tidal flow, bottom

topography and substrate, marine organisms, and propeller wash. Two detached

sonic transmitters were recovered during the study and both displayed abrasions


and indentations on the surface.









Telemetry Overview

Five Kemp's ridley turtles were instrumented with transmitters from May to

August 1994, and ten turtles were instrumented from May to November 1995. Of

this total, only turtles with > 40 hours radio monitoring or > 40 locations were

used in the analyses of activity patterns (Table 2-1). Turtles not included either

lost their transmitters prematurely or moved out of the study area (see Site

Fidelity section of Results). Carapace lengths for turtles used in the analyses

ranged from 35 to 54 cm SCL and mass ranged from 6 to 23 kg. The total mass

of the telemetry array applied to the turtles was approximately 105 g (radio

transmitter = 58 g, tether = 11 g, and sonic transmitter = 36 g), which was less

than 2% of the mass of the smallest turtle (Table 2-1).

A minimum time to independence of 4-6 hours was obtained by calculating

the indices of autocorrelation between successive observations (Table 2-2). The

results of this analysis should be interpreted cautiously given the reduction in

sample size by deleting observations and the decreasing number of consecutive

locations with increasing time intervals. The observed time to independence may

be the result of the six hour duration of each tide in the Cedar Keys area. If turtle

movements were correlated with tidal flow, a turtle would traverse its home range

during a 6 hour tidal period. Krebs (1989) noted that ecological estimates could

be biased if the sampling interval of a systematic sample corresponds with a

periodic trend in environmental conditions. Sampling turtle locations at the peak

high and low tides may produce a bimodal distribution of locational data, whereas



















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Table 2-2. Indices of serial correlation for determining the time to independence
of Kemp's ridley turtle locational data. significant (p<0.05)
autocorrelation, ns no significant autocorrelation.

Hourly Indices of serial correlation
Turtle ID interval t2/r2 y
LK1 1 0.34 2.59 0.83 *
2 0.69 2.10 0.65 *
4 1.13 1.52 0.35 ns
6 1.19 1.09 0.27 ns
LK2 1 0.41 2.25 0.77 *
2 0.75 1.79 0.58 *
4 0.67 1.91 0.49 *
6 1.28* 1.13* 0.16 ns
LK3 1 0.23 2.48 0.85 *
2 0.48 1.91 0.67 *
4 0.94 1.20 0.34 *
6 1.45 0.66 ns 0.08 ns
LK4 1 0.40 1.71 0.78 *
2 0.82 1.15 0.56 *
4 1.36 0.69 0.18 ns
6 1.58 0.07 ns -0.04 ns
LK5 1 0.26 2.26 0.85 *
2 0.55 1.95 0.70 *
4 1.04 1.55 0.44 *
6 1.77 ns 0.80 0.05 ns
LK6 1 0.22 2.42 0.84 *
2 0.46 1.98 0.66 *
4 0.86 0.97 0.31 *
6 1.26 0.45 ns 0.13 ns
LK7 1 0.32 2.55 0.84 *
2 0.63 2.21 0.68 *
4 1.23 1.36 0.37 *
6 1.54 0.87 0.21 ns
LK8 1 0.16 2.29 0.90 *
2 0.29 1.93 0.79 *
4 0.64 1.20 0.51 *
6 1.08 0.85 0.21 ns
LK9 1 0.17 3.02 0.87 *
2 0.42 2.60 0.70 *
4 0.92 1.47 0.41 *
6 0.97 1.33 0.34 *









sampling at mid-tide may yield a cluster of locations in the center of the actual

home range.



Site Fidelity

Of the 15 Kemp's ridley turtles instrumented with transmitters, only one

turtle was not located for subsequent tracking. This turtle may have left the Cedar

Keys study area or its radio transmitter may have failed and sonic contact could

not be re-established due to the limited range of this latter method. Four Kemp's

ridley turtles left the tracking area and were not included in the analyses owing to

insufficient data. One turtle traveled over 8 km to the east-southeast of South Bar

Light, possibly to Waccasassa Reefs, and returned to the study area 7 days later.

Two other turtles traveled approximately 7.5 km to the west-southwest of South

Bar Light to an unnamed ship channel. One of these turtles was tracked leaving

the study area through the channel separating the Cedar Keys and Atsena Otie

Key (Fig. 2-2). Both turtles were located in the vicinity of Corrigan Reef 2 3 days

later. The turtle that was tracked westward was located near South Bar Light

over a two month period before being recaptured and re-instrumented, and was

at large for a total of 93 days. The fourth turtle traveled approximately 7 km to the

south after the passage of a cold front in late October 1995 and remained in this

area for another two weeks before contact was lost.

Kemp's ridley turtles used in activity pattern analyses were located in the

Cedar Keys study area up to 66 days after initial capture (Table 2-1). The

locations of six of the turtles were aggregated within 4.25 km of Corrigan Reef









and the channel markers (Marker #4 and South Bar Light) south of the reef (Fig.

2-3). The other three turtles were located between 1.2 6.25 km to the south and

east of the reef and markers (Fig. 2-3). Two turtles (LK1 and LK9) were

recaptures from previous tagging studies at Corrigan Reef and had been at large

for 3 4 years prior to telemetric monitoring (Table 2-1). These turtles and three

others (LK2, LK4, and LK8) occupied 4.9 12.9 km2 home range areas with a

gradual increase in size during their respective monitoring periods (Fig. 2-4). In

contrast, four turtles (LK3, LK5, LK6, and LK7) occupied 18.0 29.5 km2 home

range areas with periodic increases of 10 20 km2 in home range size (Fig 2-4).

Home range area was not significantly correlated with carapace length or mass

(Spearman corr. coeff.=0.17, p=0.67).



Tidal Orientation

The mean of mean turtle bearings was 48 490 for incoming tides and

232 41 0 for falling tides (Table 2-3). The mean tidal bearings for 1995 were 37

90 (r=0.9879, n=113) for incoming tides and 234 90 (r=0.9867, n=149) for

falling tides. The second-order samples of turtle bearings differed significantly

from randomness for both the incoming tides (u=2.90, 0.001
falling tides (u=3.30, p<0.005), indicating that the mean bearings of turtles were

clustered around the mean bearings of the tidal states (Fig. 2-5).

Mean vector lengths were low for incoming tides (Table 2-3) and mean

angular deviations ranged from 690 to 134. Mean vector lengths for falling tides

were relatively higher, indicating an increased concentration of bearings, and















LK1
5.82 km2












V LK2

12.89 km2













YY Y y 29.51 km2






Figure 2-3. Locations and home ranges of Kemp's ridley turtles relative to
Corrigan Reef (black polygons). Squares and triangles represent
channel markers and stars denote the release site of each turtle.
Numbers indicate the total area of the home range.

















LK4
11.40 km2












LK5
25.85 km2












LK6
17.97 km2


Figure 2-3. continued.
















LK7
19.74 km2












LK8
6.66 km2












LK9
4.92 km2


Figure 2-3. continued.









30
20- LK1
10-
0
0 10 20 30 40 50 60 70


30
20-
LK2
10-

0 10 20 30 40 50 60 70

E
30




20
0 -LK3
) 10


( 0 10 20 30 40 50 60 70
E

30
20-
LK4




10 -
0 10 20 30 40 50 60 70


30-





0 10 20 30 40 50 60 70

Number of locations





Figure 2-4. Home range area versus number of locations for Kemp's ridley
turtles.











30
20 -
2 LK6
10


0 10 20 30 40 50 60 70


30

E 20
LK7
E 10 -

0 10 20 30 40 50 60 70
0)
30
E 20-
S 20LK8
10-


0 10 20 30 40 50 60 70


30-
20-
LK9
10-
0
0 10 20 30 40 50 60 70

Number of locations


Figure 2-4. continued.












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m _0






















c c
-0






oo-0


C C

C C








CN
4--





















L J_
0)0





NC C

.0)^
U-









mean angular deviations ranged from 560 to 1140. The two datasets with the

smallest sample sizes (LK2, falling tide and LK4, incoming tide) exhibited

intermediate mean vector lengths, although that of LK4 was also the highest for

incoming tides. The distribution of bearings and hourly distances by tide state

(Fig. 2-6) indicated three patterns of orientation: undirected movements less than

500 m (LK6 incoming and LK9 incoming), movements perpendicular to the

direction tidal flow (LK1 falling and LK8 falling), and movements corresponding

to the direction of the tide (LK3 falling and LK7 falling). The first two patterns

resulted in decreased mean vector lengths and increased angular deviations.



Rate of Movement

The mean rate of movement (ROM) for all turtles combined was

0.4370.331 km/hr (range: 0.004 1.758 km/hr). There was a significant

difference (X2=34.31, p=0.0001) among the ROM of individual turtles. LK3 had

the highest mean ROM (Table 2-4), which was significantly greater than those of

LK1, LK8, and LK9. LK3 had the highest recorded ROM, and 18.3% of the

observations for LK3 were greater than 1 km/hr. Conversely, LK8 had the lowest

mean ROM (Table 2-4), which was significantly lower than the rates of all turtles

except LK1 and LK9. LK8 was the smallest turtle tracked in this study (Table 2-

1), but mean ROM of turtles was not significantly correlated with carapace length

or mass (Spearman corr. coeff.=0.57, p=0.11).

Only Kemp's ridley turtles tracked in 1995 had sufficient 24 hr data to test

for time interval patterns of ROM. There was a trend for higher mean ROM









Incoming Tides


0.00


315.00



270.0



225.00


180.00


0.00


315.00



270.0



225.00




315.00



270.0



225.00


0.00


45.00


90.00


135.0


LK1


315.00


270.00


225.0


LK2


90.00


270.'


45.00



90.00



135.00


180.00


0.00


45.00



) 90.00


135.00


180.00


0.00


.45.00


90.00


135.00


LK3


315.00


270.00


225.00


180.00


45.00


90.00


135.00


180.00


Figure 2-6. Hourly bearings and distances traveled by tide state for Kemp's ridley
turtles. Black arrows indicate the mean bearings for turtles and white
arrows indicate mean tidal bearings for 1995.


Falling Tides


00








Incoming Tides


0.00


315.00


270.00


225.00


LK4


45.00


90.00


135.00


315.00


270.00


225.00


180.00


0.00


315.00


270.00


225.00


0.00


45.00


) 90.00


135.00


180.00


0.00


45.00


90.00


LK5


270.00


135.00


180.00


0.00


315.00


270.00 (


225.00


180.00


180.00


0.00


LK6


90.00


315.0


270.00


225.00


45.0


) 90.00


135.00


180.00


Figure 2-6. continued.


45.00


) 90.00


135.00


Falling Tides










Incoming Tides


0.00


315.00



270.0



225.00





315.00



270.00 (



225.00


0.00


LK7


90.00


315.00


270.00


225.00


180.00


45.00



) 90.00



135.00


180.00


0.00


45.00


LK8


90.00


135.00


315.00


270.00


225.00


180.00


0.00


315.0



270.00 (



225.00


LK9


270.00


180.00


0.00


45.0


90.00


135.00


180.00


Figure 2-6. continued.


45.00


90.00


135.00


Falling Tides









Table 2-4.


Turtle
ID


Mean rate of movement and percent composition of movement rates
for Kemp's ridley turtles. Standard deviations are given in
parentheses. Means that share the same superscript are not


significantly
procedure.

Mean
rate of
movement


LK1 0.391 a,d
(0.308)
LK2 0.487 a,b
(0.324)
LK3 0.600 b
(0.407)
LK4 0.441 a,b,c
(0.282)
LK5 0.478 a,b
(0.366)
LK6 0.474 a,b
(0.326)
LK7 0.524 b
(0.329)
LK8 0.274 d
(0.210)
LK9 0.338 c,d
(0.282)


different using the nonparametric multiple comparison


<0.5

66.1

53.7

47.7

56.8

58.0

57.6

50.0

84.9

71.4


Rate of movement (km/hr)
0.5-1.0 1.0-1.5


30.5

41.5

34.1

40.9

32.0

37.3

38.9

15.1

28.6


> 1.5


3.4

4.9

13.7

2.3

10.0

5.1

11.1

0.0

0.0








during the day for 1995 turtles combined and for individual turtles except LK9

(Table 2-5). However, only the mean ROM of LK7 was significantly greater (X2=

7.87, p=0.005) during the 12 hr day. The mean ROM of this turtle was also

significantly different among the 4 level time intervals (X2=9.53, p=0.02), but the

nonparametric multiple comparison procedure failed to indicate which of the

levels differed significantly.

Mean ROM was significantly greater on the falling tide (Table 2-6) for all

Kemp's ridley turtles combined (X2= 7.11, p=0.008) and turtles tracked in 1995

(X2= 4.11, p=0.04), but was not significantly different for turtles tracked in 1994

(X2= 3.19, p=0.07). There was a trend for higher mean ROM on the falling tide for

6 of the 9 turtles (Table 2-6), but the difference was only significant for LK2 (X2=

5.98, p=0.014) and LK6 (X2= 7.22, p=0.007). Mean ROM of individual turtles

differed significantly by tidal state (falling tide: X2= 28.02, p=0.0005; incoming

tide: X2= 16.13, p=0.041).

The tide flow data collected in 1995 indicated a trend for higher mean tidal

velocities on the incoming tides (Table 2-6), but the difference between tidal

states was not significant. For the combined data of 1995, there was a significant

positive correlation between tidal speeds and turtle ROM on both falling

(Spearman corr. coeff.=0.196, p=0.02) and incoming tides (Spearman corr.

coeff.=0.232, p=0.01). For individual turtles, however, the correlation was only

significant for the falling tides of LK7 and the incoming tides of LK8.









Mean rate of movement (km/hr) for telemetered Kemp's ridley turtles
by time of day (W dawn, D day, K dusk, and N night). A >
symbol indicates a significant difference between time intervals using
the Kruskal-Wallis test for two levels and the nonparametric multiple
comparison procedure for four levels.


Turtle
ID
1995 turtles
combined

LK5

LK6


LK7

LK8

LK9


Two level
intervals
D N
0.464 0.374


D
0.532
D
0.520
D
0.641
D
0.278
N
0.354


N
0.339
N
0.444
> N
0.416
N
0.269
D
0.319


Time of day
Four level
intervals
D K N W
0.508 0.390 0.377 0.353


D
0.557
D
0.567


- K
0.466
- W
0.498


- N
0.305
- K
0.462


- W

- N
0.422


D N K W
0.718 0.477 0.408 0.370


D
0.320
K
0.470


- N W K
0.308 0.289 0.141


- D
0.316


- N
0.314


- W
0.261


Table 2-5.









Mean rate of movement (km/hr) for Kemp's ridley turtles and mean
tidal speed (km/hr) by tidal state. A < symbol indicates a significant
difference between tidal states using the Kruskal-Wallis test.


Mean rate of movement


Turtle
ID
All turtles
combined
1994 turtles
combined
1995 turtles
combined
LK1

LK2

LK3

LK4


Incoming
tide


Falling
tide


Mean tidal speed
Incoming Falling
tide tide


0.394 < 0.476


0.424


- 0.509


0.371 < 0.456

0.392 0.377

0.371 < 0.663

0.538 0.675

0.414 0.452


0.508


- 0.413


- 0.538


0.360 < 0.577


- 0.498

- 0.296


0.472

0.616

0.508

0.359


0.352 0.326 0.586


- 0.447

- 0.477

- 0.393

- 0.271

- 0.448


Table 2-6.


0.333


LK5

LK6

LK7

LK8

LK9


0.552

0.254









Respiratory Behavior

Field observations indicated that Kemp's ridley turtles exhibited surface

durations of 1-2 seconds and submergence durations of 1-2 minutes upon

release and continuing for several hours. This pattern was probably in response

to the stress of capture and handling, and these data were therefore not included

in behavioral analyses. Telemetered turtles exhibited longer surface and

submergence durations after the 24-hour acclimation period. Presumably, a 24-

hr period of recovery was adequate because this type of respiratory pattern

continued through the remainder of the monitoring sessions.

The mean surface duration for all turtles combined was 1815 seconds

(range: 1 88 seconds) and the mean submergence duration was 8.46.4

minutes (range: 0.2 60.0 minutes). However, there were significant differences

in the mean surface durations (X2=368.5, p=0.0001) and submergence durations

(X2=375.1, p=0.0001) among individual turtles (Table 2-7). The mean surface and

submergence durations for LK6 and LK7 were significantly less than those of the

other turtles, and 58% of the surface durations for these two turtles were less

than 10 seconds (Fig. 2-7). Furthermore, LK6 and LK7 also exhibited significantly

higher mean numbers of surfacings per hour (Table 2-7). Both of these turtles

had injuries to their rear flippers (Table 2-1), though LK1 had the same type of

wounds and did not display a similar respiratory pattern.

Telemetered Kemp's ridley turtles spent 95.7 97.0 % of their time

submerged (Table 2-7). Despite the increased frequency of surfacings and

shorter respiratory durations, LK7 exhibited the longest surface duration









Summary of the surface and submergence durations for telemetered
Kemp's ridley turtles. Standard deviations are given in parentheses.
Means that share the same superscript are not significantly different
using the nonparametric multiple comparison procedure.


Mean number of
surfacings per
hour
5.6 a,c
(1.5)
4.9 a,c
(1.9)
6.3 a
(3.1)
9.6 b
(4.1)
9.8 b
(4.2)
5.9 a,c
(2.9)
5.0 0
(2.1)


Mean surface
duration
(sec.)
22.8 a
(15.1)
17.7
(13.7)c
23.9 a,b
(15.2)
11.1
(8.8)d
14.8
(13.6)e
22.3 a
(14.8)
25.9 b
(16.2)


Mean submergence
duration
(min.)
10.68 a,b
(6.45)
12.15 a
(8.86)
9.05 c
(5.67)
5.95 d
(5.56)
5.90 d
(4.48)
9.74 b,c
(5.97)
11.32 a
(6.28)


Percent
time
submerged
96.5

97.6

95.7

97.0

95.9

96.3

96.3


Table 2-7.


Turtle
ID
LK1

LK2

LK4

LK6

LK7

LK8

LK9










200 n = 271
100 LK1
0-
0 10 20 30 40 50 60 70 80 90

200
200 :n = 216
100- LK2

0 10 20 30 40 50 60 70 80 90

200
n = 386
100- LK4
0 ......
0 10 20 30 40 50 60 70 80 90
0)
C
o 200
100 ** >t. n =585 LK6


( 0 10 20 30 40 50 60 70 80 90
-0
D 200
zt n = 550







100- LK8
4- 0







0 10 20 30 40 50 60 70 80 90
200=5






z L. n = 267
100- o1 LK9

0 10 20 30 40 50 60 70 80 90

Surface Duration (seconds)




Figure 2-7. Frequency distributions of surfacing duration (10-second intervals)
for Kemp's ridley turtles. Numbers indicate total number of
surfacings.
surfaci ngs.









(88 seconds) used in the analyses. However, surface durations of 4-8 minutes

were recorded for two of the turtles not included in these analyses owing to

insufficient data. The longer surface durations recorded for these turtles may be

indicative of basking behavior. Non-telemetered Kemp's ridley turtles were

observed floating on the surface for extended periods of time, and one such turtle

appeared to be resting (motionless with foreflippers tucked laterally) within

seagrass flotsam.

Mean surface durations were not significantly different during the two 12

hour time intervals for all turtles combined (Table 2-8). However, the combined

data for each year indicated a significantly longer mean surface duration during

the 12-hour day for turtles tracked in 1994 and during the 12-hour night for turtles

tracked in 1995. This discrepancy may have resulted from sampling error as

1994 turtles were not systematically monitored for a full 24 hour period. The

mean surface duration during the 8-hour night was significantly longer than the

4-hour dusk and dawn for all turtles combined, and was significantly longer than

the other four level intervals for turtles tracked in 1995 (Table 2-8).

Mean submergence durations were significantly longer during the 12-hour

night for the combined data of all turtles and turtles tracked during each year

(Table 2-9). For all turtles combined, the mean submergence duration during the

8 hour night was significantly longer than those during the 8-hour day and 4-hour

dusk, and the mean submergence duration during the 4-hour dawn was

significantly longer than that of the 4-hour dusk. For turtles tracked in 1995, the









Mean surface durations (nearest second) of Kemp's ridley turtles by
time of day (W dawn, D day, K dusk, and N night). A > symbol
indicates a significant difference between time intervals using the
Kruskal-Wallis test for two levels and the nonparametric multiple
comparison procedure for four levels. Parentheses were used to
consolidate significant differences.


Turtle
ID
All turtles
combined

1994 turtles
combined

1995 turtles
combined

LK1
LK2
LK4
LK6
LK7
LK8
LK9


Two level intervals


N19 D18


D23 > N19


N18 > D15

D24 > N19
D18- N17
D24 N22
N12 D10
N16 D14
N31 > D17
N27 D25


Time of day
Four level intervals

(N20 > W17 K17) D19


D19-W17- K16- N14


N17 > D14-W13- K12

K27 D24 -W19 N19
K19-W19- D17- N17
W25 D24 N24 K23
N14 K12 D10 > W7
(N18 > K12 -W12)- D15
N36-W28 > D18- K16
(N29 > K21) D29 W24


Table 2-8.









Mean submergence durations (nearest second) of Kemp's ridley
turtles by time of day (W dawn, D day, K dusk, and N night). A
> symbol indicates a significant difference between time intervals
using the Kruskal-Wallis test for two levels and the nonparametric
multiple comparison procedure for four levels. Parentheses were used
to consolidate significant differences.


Turtle
ID
All turtles
combined

1994 turtles
combined

1995 turtles
combined

LK1
LK2
LK4
LK6
LK7
LK8
LK9


Two level intervals


N523 > D494


N652 > D609


N491 > D410

D647 N625
N739 D724
N568 D539
N401 > D311
N362 D346
N743 > D493
N746> D619


Time of day
Four level intervals


N545 > D497 K468 & W520 > K468


W649 K642 N639 D596


N521 W476 > D404 K394

W707 K699 D640 N542
N773 D751 K712 W608
W611 N596 K560 D524
N437 W367 > K325 D288
N379 W358 D351 K320
N793 W709 > K503 D476
(N817 D715 > K522) W675


Table 2-9.









mean submergence durations during the 8-hour night and 4-hour dawn were

significantly longer than those during the 8-hour day and 4-hour dusk.

There were significant correlations between ROM, number of surfacings,

and surface and submergence durations for the combined data of all turtles and

turtles tracked in 1995, though the significance of these relationships varied for

turtles tracked in 1994 and individual turtles (Table 2-10). Increased ROMs

corresponded to increased number of surfacings and decreased surface and

submergence durations. The number of surfacings decreased with increasing

surface and submergence durations, and increased surface durations

corresponded to increased submergence durations.

There were trends for decreasing number of surfacings and surface

durations and increasing submergence durations with both increasing carapace

length and mass (body size), but the correlations between these variables were

not significant. The data of LK6 and LK7 were omitted because of their

significantly different respiratory pattern. Subsequently, there were significant

positive correlations (Spearman corr. coeff.=0.9, p=0.04) between mean

submergence duration and body size, and significant negative correlations

(Spearman corr. coeff.=-0.9, p=0.04) between mean number of surfacings and

body size. The largest turtle (LK2; 54.0 cm SCL) exhibited the longest

submergence duration (59 minutes). However, submergence durations of 71-84

minutes were recorded for a smaller turtle (36.8 cm SCL) not included in these

analyses owing to insufficient data. This turtle was monitored later in the year

(late October and early November) than any of the other turtles, during a period









Table 2-10.


Spearman correlation analyses of the rate of movement (km/hr),
number of surfacings per hour, and mean hourly surface and
submergence durations for Kemp's ridley turtles. Number of
surfacings and surface/submergence durations were pooled within
the time intervals of consecutive locations. P-values are in
parentheses and significant correlations are in bold.


1994 turtles
combined


No. of surfacings


Surface duration

Submergence duration


No. of surfacings


Surface duration

Submergence duration


1995 turtles
combined


No. of surfacings


Surface duration

Submergence duration


No. of surfacings


Surface duration

Submergence duration


No. of surfacings


Surface duration

Submergence duration


Turtle ID
All turtles
combined


Rate of
movement
0.3081
(0.0001)
-0.2911
(0.0001)
-0.2911
(0.0001)

0.1438
(0.1155)
-0.2809
(0.0018)
-0.1655
(0.0697)

0.4270
(0.0001)
-0.3145
(0.0001)
-0.3963
(0.0001)

-0.0345
(0.8329)
-0.2047
(0.2051)
-0.0146
(0.9286)

0.1676
(0.3145)
-0.5295
(0.0006)
-0.2352
(0.1553)


No. of
surfacings


-0.6704
(0.0001)
-0.9588
(0.0001)


-0.3523
(0.0001)
-0.9197
(0.0001)


-0.8079
(0.0001)
-0.9735
(0.0001)



-0.2581
(0.1077)
-0.8456
(0.0001)



-0.1950
(0.2406)
-0.9269
(0.0001)


LK1


Surface
duration


0.6621
(0.0001)


0.3329
(0.0002)


0.8088
(0.0001)






0.2197
(0.1731)






0.2818
(0.0866)


LK2








Table 2-10. continued.

Rate of No. of Surface
Turtle ID movement surfacings duration
LK4 No. of surfacings 0.3156
(0.0393)
Surface duration -0.2030 -0.7875
(0.1918) (0.0001)
Submergence duration -0.2456 -0.9449 0.7708
(0.1124) (0.0001) (0.0001)

LK6 No. of surfacings 0.3633
(0.0047)
Surface duration -0.3190 -0.6826
(0.0138) (0.0001)
Submergence duration -0.3248 -0.9736 0.6287
(0.0121) (0.0001) (0.0001)

LK7 No. of surfacings 0.3903
(0.0035)
Surface duration -0.3004 -0.7442
(0.0273) (0.0001)
Submergence duration -0.3361 -0.9765 0.7330
(0.0130) (0.0001) (0.0001)

LK8 No. of surfacings 0.0808
(0.5651)
Surface duration 0.2766 -0.6421
(0.0450) (0.0001)
Submergence duration 0.1652 -0.9083 0.6896
(0.2372) (0.0001) (0.0001)

LK9 No. of surfacings 0.5899
(0.0001)
Surface duration -0.3454 -0.6855
(0.0151) (0.0001)
Submergence duration -0.5495 -0.8959 0.7461
(0.0001) (0.0001) (0.0001)









when water temperature typically decreases (Schmid, 1998). In fact, the longer

submergence durations of this smaller turtle were recorded after the passage of

a cold front, indicating that the respiratory behavior of Kemp's ridley may also be

correlated with seasonal changes in environmental conditions.



Discussion



The Kemp's ridley turtles tracked in the present study typically remained in

the vicinity of Corrigan Reef complex and, with the exception of two turtles, the

few that left soon returned to areas they had previously occupied. Kemp's ridley

turtles utilized relatively confined areas for the duration of the two-week

monitoring period and continued for at least 2-3 months. This indicates that

turtles may reside within this region for the duration of their seasonal occurrence

(April to November; Schmid, 1998), but long-term tracking (i.e., 6-8 months) is

needed to determine the extent of their fidelity within a season. Kemp's ridley

turtles also return to Corrigan Reef between seasons as evidenced by the

multiannual recaptures of two turtles prior to telemetric monitoring. Between

season site fidelity could be investigated by re-instrumenting turtles over

consecutive years and comparing their locations each year. However, a much

larger sample size would be required owing to the low probability of recapturing a

previously telemetered turtle during subsequent years.

Approximately half of the telemetered turtles occupied small and stable

home range areas around Corrigan Reef. The home range areas of the other









turtles were larger owing to occasional movements to other areas around the

intertidal oyster reef. These excursions may represent turtles searching for more

favorable foraging areas, and suggest turtles may periodically expand their

ranges to prevent over-exploitation of resources. There was considerable spatial

overlap in the home ranges of individual Kemp's ridley turtles, particularly around

the southern portion of Corrigan Reef, but the data for each turtle were collected

during different time periods. Interactions among turtles (such as competition or

territoriality) are not known, and there is no evidence to suggest mutually

exclusive ranges. On one occasion, the sonic signals of 2 turtles were received

while tracking a third turtle, indicating a close proximity among the turtles given

the limited range of the sonic transmitters. However, the locations of all the

telemetered animals would have to be collected at the same time in order to

determine any possible associations between turtles (White and Garrott, 1990).

Contrary to Byles' (1988) observations in Chesapeake Bay, the Kemp's

ridley turtles in the present study oriented their movements with the direction of

the prevailing tide, and increased their rate of movement with increasing tidal

velocity. The difference in behavior between studies may represent

acclimatization by the turtles to regional differences in tidal conditions. Tidal

currents in the Cedar Keys area are relatively strong, especially in the channels

that cut through the flats and shoals. As pointed out by Byles (1988), movement

with or perpendicular to the tidal flow would be energetically beneficial to a turtle.

Comparatively, the tidal flow on the shallow seagrass beds of Chesapeake Bay

may not be as strong, resulting in movements by Kemp's ridley turtles that









appear to be non-directed. Non-directed movements have also been reported for

Kemp's ridley turtles in the bays of New York Sound (Standora et al., 1990;

Morreale and Standora, 1998), though possible interactions with tidal flow were

not presented. Despite significant tidal orientation, Kemp's ridley turtles in the

Cedar Keys also exhibited extended (> 2 hours) periods of little or no directed

movement regardless of the tidal state. During daylight hours, telemetered turtles

were observed surfacing toward the direction of tidal flow when remaining

relatively stationary. Apparently, the turtles were swimming against the tidal

current while ascending and descending in order to maintain a fixed position.

Since turtles were not observed underwater, it is not known whether these

stationary periods represent resting at a specific site on the bottom or actively

foraging within a confined area. Resting and maintaining a fixed location against

the tide would be energetically disadvantageous, while feeding would offset the

expenditure of swimming against the current. Therefore, if turtles are optimizing

their swimming energetic, it is likely that turtles are foraging during these

stationary periods.

There is very little information available on the rate of movement of

Kemp's ridley turtles. Renaud (1995) reported an overall mean swimming velocity

of 1.0 km/hr, with individual mean velocities of 0.7 to 11.0 km/hr. Gitschlag

(1996) recorded a mean rate of movement of 0.82 km/hr for an adult-sized

female on the Atlantic coast. However, both of these studies employed satellite

telemetry and the authors expressed caution on interpreting these values owing

to the lack of accuracy in estimating turtle locations with this telemetric method.









In the present study, the mean rate of movement for Kemp's ridley was 0.44

km/hr with individual mean rates of 0.27 to 0.60 km/hr. The intensive and

systematic sonic tracking of turtles, coupled with the locational accuracy of

differentially corrected GPS, allowed for precise calculations of travel rates for

Kemp's ridley turtles. In addition to differences in spatial accuracy, the time

scales between telemetric methodologies are different and may have affected the

calculation of overall rates of movement. Nonetheless, the values reported by

each study appear consistent with the activities of the turtles. With the exception

of a single turtle in the Gulf, the studies using satellite telemetry were tracking

Kemp's ridley turtles migrating along the Atlantic coast during fall and winter,

when higher rates of movement would be expected. Gitschlag (1996) tracked two

other turtles with radio and sonic telemetry that also had high rates of movement

during their southerly migration, though the mean values were not reported. The

Kemp's ridley turtles tracked in the present study were utilizing summer foraging

grounds, when lower rates of movement would be expected, although their rates

of movement are likely to increase when they depart the nearshore waters of the

Cedar Keys during the fall.

Radio and satellite transmitters have been used to investigate the

respiratory behavior of Kemp's ridley turtles, but comparisons among studies are

confounded by differences between the telemetric methodologies. The data

obtained from satellite transmitters are in terms of submergence patterns and are

summarized in 12-hour intervals, whereas the data obtained from radio

transmitters are in terms of surfacing patterns and are collected consecutively.









Nonetheless, surface durations can be compared among studies using radio

telemetry, and overall submergence behavior can be compared among all

studies. The mean surface duration for subadult turtles in the present study is

slightly less than that of interesting females, but is 4 and 7 times less than the

durations reported for subadults on the Atlantic coast (Table 2-11). Differences

in the attachment of the radio transmitter and the activities of the turtles may

explain the discrepancy. Byles (1988) used one-meter lanyards, compared to the

approximately 25-36 cm tether lengths used herein, which could have resulted in

longer surface duration of the radio transmitters. The turtles tracked by Gitschlag

(1996) were actively migrating southward, and the longer surface durations he

recorded may have been the result of their travelling in relatively deeper and

cooler waters. Despite similarities in percent time submerged, the mean

submergence duration in the present study was shorter than that reported by any

other investigator (Table 2-11). No explanation is offered other than a possible

combination of the differences between studies (type and attachment of

transmitter, depth and temperature of water, and developmental stage and

activities of turtles).

Temperature is the main environmental factor influencing the daily

activities of terrestrial animals (Cloudsley-Thompson, 1961). However, daily

temperature fluctuations in the aquatic environment are minimized owing to the

higher thermal capacity of water. Consequently, the ecological significance of diel

patterns in aquatic animals is less clear, though in most cases it is probably

related to food acquisition (Cloudsley-Thompson, 1961). The data available for







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marine turtles provide support for this supposition. Diel activity patterns have

been reported for subadult hawksbill (van Dam and Diez, 1998) and green turtles

(Bjorndal, 1980; Mendonga, 1983; Ogden et al., 1983), but have not been

observed in subadult loggerhead turtles (Byles, 1988) or subadult and post-

nesting Kemp's ridley turtles (Byles, 1988, 1989). The spongivorous hawksbill

and herbivorous green turtle fed on sedentary food items that tend to be

concentrated in certain areas. Both species forage during daylight and return to

resting sites at night. By comparison, the carnivorous loggerhead and Kemp's

ridley turtles feed on benthic invertebrates, particularly molluscs by the former

(Dodd, 1988) and crabs by the latter (Shaver, 1991), and their prey may be

widely dispersed, nocturnally active, and relatively mobile. Nightly resting sites

were not recorded for either species, indicating that they may be feeding

throughout a 24-hour period. Nocturnal feeding has also been hypothesized for

inter-nesting leatherback turtles, Dermochelys coriacea, as their dive patterns

were correlated with the diel migration of the zooplankton that they feed upon

(Eckert et al., 1989)

A few telemetric studies of Kemp's ridley turtles have identified the timing

of daily activities, but none has suggested reasons for these patterns. Although

Kemp's ridley turtles in the present study did not exhibit significant diel patterns of

movement, there was a trend for a higher rate of diurnal movement and the

significantly longer submergence durations during the night suggest reduced

nocturnal movement. Nevertheless, turtles also exhibited periods of little or no

movement during all hours of the day and night. Animals engaged in equal









activities throughout a 24-hour period are referred to as nychthemeral, and the

adaptive significance of this type of pattern is that it allows for regular bouts of

feeding, which in turn should maximize feeding efficiency (Maier and White,

1998). If Kemp's ridley turtles continue to feed at night, they must be using

olfactory or auditory cues to find their prey. These methods of prey detection may

also be used during the day as the turbid waters surrounding Corrigan Reef limit

light penetration and subsequently reduce visibility underwater.

The activity patterns of Kemp's ridley turtles in the Cedar Keys may

coincide with the activities of their prey. Stone crabs, Menippe spp., and blue

crabs, Callinectes sapidus, were identified as important food items for Kemp's

ridley turtles captured in the vicinity of Corrigan Reef (Schmid, 1998). The stone

crab is nocturnally active and capable of sound production by way of stridulating

organs on the chela (Powell and Gunter, 1968; Bender, 1971). The possibility of

auditory detection of prey could be investigated by capturing turtles and holding

them for fecal sample analysis, then exposing turtles that have ingested stone

crabs to stridulation and recording their behavior in response to the sound.

Telemetric studies of foraging blue crabs indicated that their movements were

non-directed with no diel pattern (Hines and Wolcott, 1990; Nye, 1990), although

an increase in diurnal movements was noted for premolt crabs (Wolcott and

Hines, 1990).

Marine turtles rely on aerobic metabolism during routine activities, and

oxygen consumption has been used as an indirect measure of their energy

consumption (Wyneken, 1997, and references therein). Captive green (Prange,









1976; Butler et al., 1984) and loggerhead turtles (Lutz et al., 1989) demonstrated

a three-fold increase in oxygen consumption between resting and moderate

swimming speeds, and a corresponding increase in respiratory frequency.

Although there are no quantitative data on oxygen consumption by Kemp's ridley

turtles, the correlation of movement rates with respiratory activities in the present

study is in agreement with the results of swimming performance tests. Stabenau

et al. (1992) indicated that the breathing frequency in Kemp's ridley turtles was

higher than that of green turtles swimming under similar laboratory conditions

(Butler et al., 1984). Excluding the dissimilarities in turtle sizes and experimental

protocols used in each study, this would indicate that there are differences in

oxygen consumption, and therefore metabolic rate, between species, and that

the metabolic rate of Kemp's ridley turtles is higher than that of green turtles.

Inter-specific differences in the breathing frequencies of wild turtles could be

investigated by telemetrically monitoring similar-size individuals of both species

at the same time and in the same general area, and comparing their patterns of

movement and respiratory durations.

Marine turtles are ectothermic and therefore rely on the temperature of the

surrounding water to regulate body temperature. This influences their activities

as thermoregulation is achieved by moving between contrasting thermal

environments (Lillywhite, 1987). Cooler water temperatures would decrease the

metabolic rate of an ectotherm, and, as a consequence, turtles would be

expected to have lower number of surfacings and longer inter-respiratory

durations. One of the telemetered turtles not included in the present analyses









moved southward to relatively deeper waters after the passage of a November

cold front, and subsequently exhibited fewer surfacings with longer submergence

durations. As noted in the preceding paragraph, this seasonal influence on

activities and respiratory behavior may explain some of the differences among

telemetric studies. The question remains as to whether the turtles from the Cedar

Keys continue to move southward along the coast as the nearshore water

temperature decreases or move to the deeper, warmer waters offshore. Satellite

telemetry has been employed to document the seasonal activity patterns of

Kemp's ridley turtles along the Atlantic coast (Standora et al., 1992; Gitschlag,

1996; Morreale and Standora, 1998) and similar methods should be employed to

investigate their winter activities in the northeastern Gulf of Mexico.

Energetics also plays an important role in the spatial distribution of marine

turtles during their seasonal occurrence in coastal-benthic habitats. Ogren (1989)

indicated that smaller turtles have less lung capacity and higher oxygen

consumption, which limit their dive duration, although no quantitative data were

provided to support this supposition. Nonetheless, he therefore hypothesized that

smaller turtles enhance their feeding efficiency by inhabiting shallower waters.

Smaller turtles would also be expected to occupy smaller foraging ranges to

meet their energy demands, as originally proposed by McNab (1963) and as

observed for green turtles by Mendonga (1983). In the present study, there were

indications of a relationship between respiratory durations and body size for

Kemp's ridley turtles occurring in relatively shallow depths. The results of these

analyses, however, represent the upper portion of the size range of subadult









Kemp's ridley turtles found in U.S. coastal waters. Similarly, the lack of

relationship between home range area and body size of Kemp's ridley turtles

may have been a result of this truncated size range. Telemetric monitoring of

smaller size classes, such as those found in the panhandle region of Florida

(Ogren, 1989), is needed to provide support for size-specific activity patterns and

home range area of subadult Kemp's ridley turtles.

A number of species must be surveyed in order to evaluate McNab's

(1963) predictions on energetic and home range size. I therefore collated the

available information on home range area and body mass for marine turtles

tracked with radio and sonic telemetry on summer foraging grounds (6 studies for

4 species; Fig. 2-8). There was a significant positive correlation (Spearman corr.

coeff.=0.56, p=0.0008) between the home range area and mass for all the

species combined, supporting McNab's (1963) prediction of increasing foraging

range with increasing size. Furthermore, the relationship for green turtles was

highly significant (Spearman corr. coeff.=0.93, p=0.0001) owing to the size-

specific foraging behavior of this species. Small green turtles forage on

macroalgae growing on reefs and jetties in close proximity to their nightly resting

sites (Wershoven and Wershoven, 1989; Guseman and Ehrhart, 1990; Renaud

et al., 1995), whereas larger green turtles forage on seagrass beds separated

from their nocturnal sites (Bjorndal, 1980; Mendonga, 1983; Ogden et al., 1983).

This pattern is supported by studies performed in the southeast U.S. and

northeast Caribbean, and does not apply throughout the range of this species.

McNab (1963) also identified food types and their relative abundance as






















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determining factors for the size of a species home range. Accordingly, the marine

turtle "croppers" (hawksbill and green turtles) feed on concentrated food sources,

and would be expected to have smaller home ranges than the "hunters" (Kemp's

ridley and loggerhead turtles). In fact, with the exception of a single loggerhead,

the home range areas of the hunters were at least seven times larger than those

of the croppers of similar size (Fig. 2-8).

Admittedly, the data available for home range analyses of marine turtles

are scant, and comparisons may be confounded by dissimilar methods among

the studies (Table 2-12). Different techniques of home range estimation and

tracking intensity have been shown to produce different estimates of home range

size for the same data (Swihart and Slade, 1985b; White and Garrott, 1990).

Only minimum area methods of home range estimation were used in the present

analyses, but tracking interval and duration varied among studies. One major

disadvantage of minimum area methods is that the size of the home range

usually increases as the number of locations increase (White and Garrott, 1990).

Furthermore, use of autocorrelated data results in underestimation of home

range size (Swihart and Slade, 1985b), although intensive sampling during a

predefined time frame precludes this effect (Otis and White, 1999). Nonetheless,

the available information for marine turtles concurred with McNab's (1963)

predictions, although more data are needed to test the validity of these

comparisons. Future telemetric investigations of marine turtles should consider

standardizing their methods of data collection and data analysis in order to

facilitate comparisons among studies.