Wyneken, Jeanette

Two species of sea turtle, loggerheads (Caretta caretta) and leatherbacks (Dermochelys
coriacea) are caught frequently as bycatch in longline fisheries. These fisheries use
hooks baited with fish or squid. Yet, leatherbacks feed on gelatinous prey while
loggerheads are carnivores. I investigated the responses of these two species to bait
odors in controlled laboratory experiments to better understand their feeding behavior
and why they interact with longlines. Both species initiated feeding behavior in the
presence of squid bait odors and just C. caretta showed feeding behavior with sardine
odors; neither responded to mackerel odors. The turtles are hooked differently on
longlines. Loggerheads are usually hooked in the mouth while leatherbacks are usually
hooked in the shoulder or flippers. Comparisons of prey attack behavior and accuracy in
apprehending a stimulus in the presence of waterborne food odors identified speciesspecific differences that may predispose the turtles to particular kinds of hooking.

Sex determination in leatherback sea turtles is directed primarily by the temperatures a
clutch experiences during the middle third of development. Warmer temperatures tend to produce females will cooler temperatures yield males. Nest temperatures can vary
spatially and temporally. During the 2010 and 2011 nesting seasons, this study estimated the hatchling sex ratio of leatherback sea turtles on Sandy Point National Wildlife Refuge (SPNWR), St. Croix, U.S. Virgin Islands. I measured sand temperatures from May- August and across the spatial range of leatherback nesting habitat. I spatially interpolated those temperatures to create maps that predicted temperatures for all nests incubating on SPWNR. Nest temperatures were also directly measured and compared with predicted nest temperatures to validate the prediction model. Sexes of dead-in-nest hatchlings and full term embryos were used to confirm the sex-temperature response. The model showed that microclimatic variation likely impacts the production of both sexes on SPNWR.

Gopher tortoise ecology is poorly understood in the rapidly developing, urbanized southeastern end of its range. This study reports on a population at Florida Atlantic University in Boca Raton, Florida. Burrow surveys were conducted from May to July 2003 and May to August 2004. Burrows were marked and mapped as was vegetative cover. Burrow locations were tested against vegetative cover height and soil types. Burrow locations did not differ among soil types. The densest concentrations of burrows were located in areas of low, patchy vegetative cover. This is consistent with known gopher tortoise habitat preferences elsewhere in their range. Gopher tortoises on this site appeared to be acclimated to anthropogenic disturbance.

Sea turtle nests were compared to determine the effects of nest depth on hatchling anaerobic metabolism in Juno Beach, Florida, USA. In situ nests of 3 species (Caretta caretta, Chelonia mydas and Dermochelys coriacea) were compared. Relocated loggerhead nests were studied under an experimental regime. Nest temperatures and oxygen concentrations were monitored. On the night of first emergence, blood samples were taken from hatchlings resting at the nest chamber bottom and sand surface, and digging to the sand surface. Samples were analyzed for lactate concentrations. Blood lactate levels were high in hatchlings actively digging and low for those resting. Lactate levels differed among species and nest depths. Within in situ nests, actively digging green turtle hatchlings had the highest lactate, followed by loggerhead hatchlings and leatherbacks (lowest). Loggerhead hatchlings digging from deeper relocated nests had higher lactate than those digging from shallower depths.

We understand very little about the relationships between eye anatomy and visual ecology in sea turtles. Sea turtles use visual information in important contexts, such as selecting habitats, detecting predators, or locating mates or food. This study represents an effort to clarify the form/function relationship between retinal morphology and the behavioral ecology of sea turtle hatchlings. Thus, it is an important first step in relating sea turtle eye anatomy with visual ecology and relating the two to sea turtle natural history. Some organisms possess retinas that contain morphologically specialized cellular areas. The "visual streak," is one such area; receptor cells and associated interneurons are concentrated in a horizontal band in the retina. Three species of sea turtles (Chelonia mydas, Caretta caretta, and Dermochelys coriacea) possess a visual streak located along the horizontal mid-line of the retina, although they differed in streak development. The differences in streak development can be related to their ecology.

Hatchling sea turtles emerge at night from underground nests, crawl to the ocean, and swim out to sea. In this study, I determined how offshore orientation and shallow-water predation rates varied under natural (sand bottom and patch reef) and modified (submerged breakwater and open-beach hatchery) ecological circumstances. Hatchling offshore orientation in the sea was normal under all conditions; there were no significant differences in either scatter or direction among groups. However, predators (tarpon, snapper, barracuda, jacks, and grouper) took more hatchlings as they swam over submerged reefs, and after they entered the water in front of hatcheries. Predators were concentrated at both of these sites probably because prey (small fishes and invertebrates at patch reefs and turtles entering the water where nests were concentrated in hatcheries) occur in greater abundance.

Few studies document mortality rates for hatchling sea turtles during their migration away from the nesting beach. This study quantifies and compares nearshore predation rates on loggerhead hatchlings (Caretta caretta) at several locations in southern Florida. Hatchlings were followed by observers in kayaks during the first 15 min of the migration away from the beach. The overall observed predation rate (4.6%) is similar to a previous estimate (5%) from a natural high density Florida nesting beach, and lower than at a hatchery site. Predation rates were higher on Florida's southeast coast than the southwest coast. Predation increased towards the end of the hatching season. Results suggest that currently, hatchling mortality rates are relative low in Florida's shallow nearshore waters. Given the lack of growth by loggerhead populations, the cumulative mortality must be high after hatchlings depart shallow coastal waters.

Investigation of the spatio-temporal movements of leatherback sea turtles (Dermochelys coriacea) and ocean sunfishes (family Molidae), as well as analyses of their prey, support the hypothesis that they may occupy similar ecological niches. This study examined the spatial and temporal occurrences of sunfishes (Mola mola and Masturus lanceolatus) and leatherbacks in the western Atlantic Ocean and assessed dietary overlap. Analyses of leatherback and sunfish distributions, estimated from aerial surveys, showed greater spatial and temporal overlap along the Northeast coast of North America than in the Gulf of Mexico. Both species co-occur more often during warmer months. Pelagic longline fisheries bycatch data and aerial survey data revealed slightly different trends in spatio-temporal distributions. Nematocysts found within gastrointestinal tract contents of stranded animals indicate that they may feed on similar prey, including cnidarians in the classes Scyphozoa, Hydrozoa, and Cubozoa.

The sex ratios of hatchling loggerheads (Caretta caretta) were determined to provide robust assessments of regional and seasonal contributions of males and females to the population. Hatchlings from nests along the Atlantic coastline were raised to 120 g, sexed laparoscopically and verified histologically. Sex ratios differed at the beach, subseason, and subpopulation levels. There was no difference in overall sex ratios between the two study years. Average nest temperature and incubation durations were not accurate sex ratio correlates. Temperatures that produced female biased or male biased sex ratios overlapped in ranges with those producing a single sex. I found that the Transitional Range of Temperatures for loggerhead sea turtles is approximately 26.5°C--32°C, and the best correlation between average temperature and sex ratio occurred at 50--65% of incubation. Further studies are needed to define the roles of other environmental factors or the responses of tissues in loggerhead sex determination.

To improve our understanding of loggerhead life history, particularly factors affecting the duration of each age class and survivorship, detailed growth data must be interpreted. The purpose of this study was to investigate how temporal and spatial nest origin influence initial hatchling size and growth potential. Seasonal environmental fluctuations and maternal resource allocation could result in differential hatchling size and development. Hatchlings from ten sites from North Carolina to Florida representing 2 subpopulations were sampled during 3 phases of the season. The largest (WT, SCL and SCW) hatchlings came from the northernmost site with initial size decreasing as latitude decreased. Turtles deposited during the earliest phase of the nesting season grew faster than those from later phases of the season. Differences in initial size and growth potential could influence early stage survivorship as a function of size-based predation, and may imply the need for separate consideration when constructing population models.