Behaviour and Physiology: The Thermal Strategy of Leatherback Turtles

Background: Adult leatherback turtles (Dermochelys coriacea) exhibit thermal gradients between their bodies and the environment of $8uC in sub-polar waters and #4uC in the tropics. There has been no direct evidence for thermoregulation in leatherbacks although modelling and morphological studies have given an indication of how thermoregulation may be achieved. Methodology/Principal Findings: We show for the first time that leatherbacks are indeed capable of thermoregulation from studies on juvenile leatherbacks of 16 and 37 kg. In cold water (, 25uC), flipper stroke frequency increased, heat loss through the plastron, carapace and flippers was minimized, and a positive thermal gradient of up to 2.3uC was maintained between body and environment. In warm water (25 – 31uC), turtles were inactive and heat loss through their plastron, carapace and flippers increased. The thermal gradient was minimized (0.5uC). Using a scaling model, we estimate that a 300 kg adult leatherback is able to maintain a maximum thermal gradient of 18.2uC in cold sub-polar waters. Conclusions/Significance: In juvenile leatherbacks, heat gain is controlled behaviourally by increasing activity while heat flux is regulated physiologically, presumably by regulation of blood flow distribution. Hence, harnessing physiology and behaviour allows leatherbacks to keep warm while foraging in cold sub-polar waters and to prevent overheating in

Warm Water and Cool Nests Are Best. How Global Warming Might Influence Hatchling Green Turtle Swimming Performance

For sea turtles nesting on beaches surrounded by coral reefs, the most important element of hatchling recruitment is escaping predation by fish as they swim across the fringing reef, and as a consequence hatchlings that minimize their exposure to fish predation by minimizing the time spent crossing the fringing reef have a greater chance of surviving the reef crossing. One way to decrease the time required to cross the fringing reef is to maximize swimming speed. We found that both water temperature and nest temperature influence swimming performance of hatchling green turtles, but in opposite directions. Warm water increases swimming ability, with hatchling turtles swimming in warm water having a faster stroke rate, while an increase in nest temperature decreases swimming ability with hatchlings from warm nests producing less thrust per stroke

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26 degrees C were larger in size than hatchlings from 28 and 30 degrees C, whilst in the second year hatchlings from 25.5 degrees C were similar in size to hatchings from 30 degrees C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28 degrees C, hatchlings from eggs incubated at 25.5 and 26 degrees C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30 degrees C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea

Effectiveness of strategies at reducing sand temperature to mitigate potential impacts from changes in environmental temperature on sea turtle reproductive output

Sea turtle reproduction is heavily influenced by environmental temperature. Thus, projected changes in global temperatures are predicted to alter their reproductive output (e.g. hatchling sex ratio and success). Management strategies to mitigate potential threats have been identified, but little is known about their effectiveness. We tested how effective sprinkling nests with water and shading is at reducing sand temperature. We compared sand temperature at average green turtle (Chelonia mydas) nest depth in a controlled environment with 5 different treatments: (1) shade (S), (2) shade with sprinkling during the day (SD) and (3) at night (SN), and (4) sprinkling during the day (ED) and (5) at night (EN) both exposed to sunlight. Not all strategies reduced the sand temperature; treatments with sprinkling during the day and shading on rainy days had warmer temperatures (0.83 ± 1.20 °C and 0.96 ± 0.41 °C respectively) than control treatments. Sprinkling during the night at an exposed and shaded setting were most effective at reducing sand temperature (with sand temperature on average 2.23 ± 0.66 °C and 1.43 ± 0.94 °C lower than control, respectively). These strategies could potentially be effective in counteracting increases in temperature at nesting grounds used by the northern Great Barrier Reef green turtle by 2030, where predictions are for an increase of 0.2–1.8 ± 0.01–0.37 °C. The effectiveness of strategies will likely vary regionally depending on the beach environment and setting used for the strategy

The effect of incubation temperature on hatchling quality in the olive ridley turtle, Lepidochelys olivacea, from Alas Purwo National Park, East Java, Indonesia: implications for hatchery management

Nest protection through egg relocation from natural nests into protected hatcheries is a common practice used at rookeries around the world to increase hatchling recruitment into sea turtle populations. However, rarely have the impacts of this practice on hatchling recruitment and quality been assessed. This study investigated the influences of the thermal nest environment of olive ridley turtles Lepidochelys olivacea on emergence success and quality of hatchlings of hatchery nests in Alas Purwo National Park, East Java, Indonesia (2009 and 2010 nesting seasons). Nest temperatures above 34 °C for at least 3 consecutive days during incubation in the hatchery resulted in decreases in emergence success and locomotor performance of hatchlings. The use of the hatchery is recommended due to extremely high predation rate of nests left on the beach; however, altering hatchery management practice by spacing nests one meter apart and providing shade should improve hatchery outcomes now and into the future