Hawksbill turtles are picky about their water temperature

Article: Pilcher N., Perry L., Antonopoulou M., Abdel-Moati M., Abdessalaam T., Albeldawi M., Ansi M., Al-Mohannadi S., Baldwin R., Chikhi A., Das H., Hamza S., Kerr O., Kiyumi A., Mobaraki A., Suwaidi H., Suweidi A., Sawaf M., Tourenq C., Williams J., Willson A. (2014) “Short-term behavioral responses to thermal stress by hawksbill turtles in the Arabian region.” Journal of Experimental Marine Biology and Ecology 457:190-198.

Doi 10.1016/j.jembe.2014.04.002

Introduction

Several animals are ectotherms, as opposed to humans, who are endotherms. We maintain the same internal body temperature no matter what the weather is like outside. Ectotherms, however, rely on the outside environment to regulate their internal temperature. Frogs, for example, spend their days lying in the sun, not expecting to get a tan, but in order to help keep their internal heat high. In the marine environment, basking in the sun becomes slightly harder, so animals have adapted to other strategies, such as depth restrictions, dormancy, migration, and habitat selectivity based on latitude. As global water temperatures increase, the ability for marine ectotherms to regulate their body temperature and respond to these temperature shifts becomes more relevant. Raised water temperatures do have advantages, such as increasing habitat selectivity and nesting success, but it also has potentially negative impacts, such as altering sex ratios (for turtles, eggs that are warm turn into females and eggs that are cold turn into males), and even possibly shifting entire nesting seasons.

Researchers looked at the movement patterns of the hawksbill turtle in the Arabian Gulf in order to better understand their behavioral patterns in response to water temperature.

Methods

A total of 90 hawksbill turtles were tracked from ten different known nesting locations in Iran, Quatar, Oman, and in the UAE (Fig. 1). Each turtle was equipped with a satellite tracking “backpack” allowing researchers to see where each turtle was headed, its swimming speed, and where it slowed down to eat. Sea-surface temperature, height, and current patterns were also evaluated during the study.

Results and Significance

The summer months (June-August) had an averaged surface temperature of 33.6°C whereas the winter months averaged 28.2°C. As expected, warmer sea temperatures had a higher migration rate with 75% of the hawksbill migration loops beginning prior to August and 83% returning after September. Return patterns did not always follow the same track back to the starting location, however (Fig. 2). Compared with foraging turtles, the turtles on the summer loop migration had a much higher swimming speed. This, again, supports the argument for warmer water temperature influencing behavioral patterns (in this case, faster swimming speed).

Purposeful direction was also noted, as the turtles tended to swim in a north-easterly direction toward deeper, cooler waters during the summer months while in the winter months, the turtles tended to stay in the shallower, warmer waters.

Understanding how the hawksbill turtles use their habitat and where they are distributed throughout the warmer and colder months will help with conservation management strategies. These findings will hopefully show what areas need to be protected and managed in order to provide protection for the hawksbill turtles in their various life stages.

Valeska Upham

For my fisheries and aquatic science PhD I am working on how to tank raise urchins and transplant them onto reefs across the Florida Keys in order to help reverse the phase shift from algae dominated back to coral dominated.