Sea turtles

Sea turtle hatchlings face a variety of obstacles as they crawl down the beach to the ocean after emergence. One of these obstacles is Sargassum, a floating brown macroalgae, that washes up in large quantities on beaches from Florida to South America. This study examined the physiological response and physical performance of three species of sea turtle hatchlings (D. coriacea, C. caretta, and C. mydas) after crawling over various heights of Sargassum. In all three species, the addition of Sargassum significantly increased the amount of time it took to crawl down the pathway. There was no significant difference in righting response, blood glucose levels, or plasma corticosterone concentrations between different crawling treatments. During periods of high Sargassum accumulation, hatchlings will spend more time on the beach trying to navigate through the algae, leaving them vulnerable to predation for longer periods of time.

In sea turtles, body condition can be evaluated through subjective body condition scoring (BCS), calculating body condition index (BCI), and clinical blood parameters. The goal of this study was to analyze ultrasonography of subcutaneous fat depth as a method to estimate body condition in 10 green and 8 loggerhead sea turtle carcasses using two types of portable ultrasound technologies, the Ibex Evo® and the Renco Lean-Meater®. Despite the general lack of significant correlations between ultrasound-assisted, gross, and histological measurements, the dorsal shoulder and lateral neck were determined to provide the most consistent images of subcutaneous fat. Florida live-captured green turtles were sampled and ultrasound-assisted fat depth measurements were taken at the dorsal shoulder region; however, there were no significant correlations found between fat depth and BCI or blood analytes (PCV, total protein). BCI reference quartiles were created using associations between BCI and BCS to help provide biological context to BCI data and allow for rapid categorization of sea turtle body condition.

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.

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.

Under normal conditions, hatchling sea turtles crawl toward the ocean but streetlights placed on coastal roadways can attract the turtles toward land. Two light filters were designed to exclude the shorter light wavelengths most attractive to turtles. I did laboratory tests to determine if green turtle and loggerhead hatchlings oriented normally ("seaward") in the presence of filtered lighting. Light passed through either filter (#2422 acrylic and NLW) attracted the turtles unless coastal cues (an elevated horizon) were strong or background (full moon) illumination was present. Green turtles and loggerheads responded differently to the same filters, indicating that neither filter provided adequate protection for both species. I conclude that these filters fail to protect the turtles. Conventional forms of light control (shielding and/or lowering light fixtures, decreasing wattage, or turning off problem lights) remain the best way to shield turtles from the harmful effects of artificial lighting.

The reproductive success of leatherback turtles (Dermochelys coriacea) is typically the lowest of the seven sea turtle species. Why this vital rate is decreased has remained unanswered for nearly a century. Recently, detailed postmortem examination of leatherback hatchlings identified muscular pathologies that suggested possible selenium deficiency. High bodily burdens of mercury compounds are associated with selenium depletion. Selenium is a necessary detoxifying nutrient that itself can be toxic at elevated concentrations. Mercury compounds are toxicants with no known biological function. High bodily concentrations of mercury can be detrimental to marine organismal health, reproduction and survival, both directly and indirectly through inducing selenium depletion. The goals of this dissertation are to evaluate several related hypotheses to explain low leatherback nest success. ... Because leatherbacks take in high volumes of prey, high tissue concentrations of mercury and selenium can result. This study provides the first evidence that chemical contaminants may explain low reproductive success in leatherback sea turtles.

South Florida's loggerhead (Caretta caretta), green (Chelonia mydas) and leatherback (Dermochelys coriacea) sea turtles hatchling have environmentally determined sex. The in situ nest mean hatchling sex ratios (SR) were highly female-biased : loggerhead F=0.89) and green turtle F=0.81; leatherback's SR was nearly balanced (0.55F). Nest temperatures and SRs differed between leatherbacks and loggerhead and green turtles. The latter two did not differ. The loggerhead response parameters were estimated within biological limitations by both 50-65% of incubation and mean middle 1/3 temperature. The maximum middle 1/3 temperature was the best-fit predictor for green turtles. No best-fit sex ratio-temperature response could be identified for leatherbacks. Clutches incubating under natural conditions can vary greatly in SR ; TRT differences may account for differences among species' sex ratios.

The photopollution of beaches caused by artificial light sources can interfere with sea turtle hatchlings' ability to orient properly towards the sea. Exhaustion due to extended disorientation crawling may then increase hatchling mortality. This study evaluated the energetic consequences of long-distance crawls in green and loggerhead sea turtle hatchlings. Turtles crawled for 200 m or 500 m on a treadmill, followed by a 30 minute evaluation of swim performance. Metabolic activity was quantified via measures of blood glucose, blood lactate, and oxygen consumption. No significant changes in metabolism resulted from long-distance crawling activity in loggerheads ; however, loggerheads rested for extended periods of time during the crawl trials, often unresponsive to stimuli. This behavior implies that loggerhead hatchlings would be vulnerable to predation or temperature stress due to exhaustion from extended periods of crawling. Further data is required to draw any significant conclusions about long-term disorientatin crawling in green hatchlings.

Little is known about the visual capabilities of marine turtles. The ability to discriminate between colors has not been adequately demonstrated on the basis of behavioral criteria. I used a three-part methodology to determine if color discrimination occurred. FIrst, I exposed naèive, light-adapted hatchlings to either a blue, green or yellow light. I manipulated light intensity to obtain a behavioral phototaxis threshold to each color, which provided a range of intensities we knew turtles could detect. Second, I used food to train older turtles to swim toward one light color, and then to discriminate between the rewarded light and another light color ; lights were presented at intensities equally above the phototaxis threshold. Lastly, I varied light intensity so that brightness could not be used as a discrimination cue. Six turtles completed this task and showed a clear ability to select a rewarded over a non-rewarded color, regardless of stimulus intensity. Turtles most rapidly learned to associate shorter wavelengths (blue) with food. My results clearly show loggerheads have color vision. Further investigation is required to determine how marine turtles exploit this capability.