Swimming performance and metabolic rate of flatback Natator depressus and loggerhead Caretta caretta sea turtle hatchlings during the swimming frenzy

摘要

ABSTRACT: Swimming performance influences the dispersal success of sea turtle hatchlings when they first enter the water and engage in a ‘swimming frenzy’ which moves them rapidly offshore. We simultaneously measured swim thrust (in millinewtons, mN) and metabolic rate (in milliwatts, mW) of loggerhead Caretta caretta and flatback turtle Natator depressus hatchlings during the first 18 h of the swimming frenzy and compared the results with previous data from green turtle Chelonia mydas hatchlings. Metabolic rate was correlated with swim thrust in all species. In all species, swim thrust decreased sharply during the first 2 h of swimming, continued to slowly decrease until 12 h and remained constant at this lowest level until experiments ended at 18 h. Metabolic rate had a similar pattern, with a steep drop during the first 2 h followed by a less steep decrease before becoming relatively constant. Swim thrust and metabolic rate were highest in green turtle hatchlings. Flatback hatchling metabolic rate was similar to green turtle hatchlings but they weighed almost twice as much, while loggerhead hatchlings had the lowest metabolic rate. Flatback hatchling swim thrust decreased the fastest, falling below that of green turtle hatchlings within the first hour of swimming and falling below loggerhead turtle hatchlings after 12 h of swimming. These findings suggest that flatback hatchlings have a different dispersal behaviour compared to green and loggerhead hatchlings. The shorter highly vigorous swimming period of flatback turtles might be explained by the fact that they do not swim into off-shore oceanic dispersing currents, and managing their energy resources might be a strategic adaptation to survive predators in a relatively constant environment.