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

Measuring Energy Expenditure in Sub-Adult and Hatchling Sea Turtles via Accelerometry

Measuring the metabolic of sea turtles is fundamental to understanding their ecology yet the presently available methods are limited. Accelerometry is a relatively new technique for estimating metabolic rate that has shown promise with a number of species but its utility with air-breathing divers is not yet established. The present study undertakes laboratory experiments to investigate whether rate of oxygen uptake (o2) at the surface in active sub-adult green turtles Chelonia mydas and hatchling loggerhead turtles Caretta caretta correlates with overall dynamic body acceleration (ODBA), a derivative of acceleration used as a proxy for metabolic rate. Six green turtles (25–44 kg) and two loggerhead turtles (20 g) were instrumented with tri-axial acceleration logging devices and placed singly into a respirometry chamber. The green turtles were able to submerge freely within a 1.5 m deep tank and the loggerhead turtles were tethered in water 16 cm deep so that they swam at the surface. A significant prediction equation for mean o2 over an hour in a green turtle from measures of ODBA and mean flipper length (R2 = 0.56) returned a mean estimate error across turtles of 8.0%. The range of temperatures used in the green turtle experiments (22–30°C) had only a small effect on o2. A o2-ODBA equation for the loggerhead hatchling data was also significant (R2 = 0.67). Together these data indicate the potential of the accelerometry technique for estimating energy expenditure in sea turtles, which may have important applications in sea turtle diving ecology, and also in conservation such as assessing turtle survival times when trapped underwater in fishing nets

Residence and movement patterns of cownose rays Rhinoptera bonasus within a south-west Florida estuary

Between July 2003 and November 2004, 21 cownose rays Rhinoptera bonasus were tagged and tracked within Pine Island Sound estuary, Florida, using passive acoustic telemetry. Residence time of individuals ranged between 1 and 102 days. No relationship was detected between ray activity and tidal stage or time of day. Minimum convex polygons (MCP) and kernel utilization distributions (KUD) were calculated over several time frames to demonstrate the extent of an animal's home range and core areas of use. Total MCPs ranged between 0·81 and 71·78 km2 (mean = 22·01 km2), with daily MCPs as large as 25·8 km2. Total 95% KUDs ranged between 0·18 and 62·44 km2 (mean = 22·63 km2), while total 50% KUDs were smaller, ranging from 0·09 to 9·68 km2 (mean = 3·33 km2). Both MCP and KUD areas exhibited a positive relationship with residence time and R. bonasus size. As mobile, pelagic swimmers capable of traversing large distances, these data show that cownose rays travel extensively throughout this estuary, yet may remain within very small areas for extended periods

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