Abstract

Previously, we showed that during their first six days of swimming hawksbill hatchlings are less active than the hatchlings of other marine turtle species. Here, we document that hawksbills also employ slower, drag-based swimming gaits during the brief periods when they do swim. These gaits may render the turtles less conspicuous to predators that detect prey on the basis of movement. Over the 6-day period of observations, predominantly drag-based locomotion (by “rear-flipper kicking” and “dogpaddling”) was gradually replaced by a larger proportion of “power stroking”, a more powerful and faster lift-based means of locomotion. Under natural conditions, this change probably occurs after the hatchlings have reached deep water where predator concentrations are lower. Hawksbill hatchlings are smaller than those produced by most other marine turtles, suggesting that their unique migratory strategy might be correlated with insufficient power to swim rapidly. However, a comparison among species of marine turtle hatchlings suggests that size is poorly correlated with swimming speed. We hypothesize instead that both hatchling size and swimming speed independently determine vulnerability to inshore fish predators. Thus, hawksbills may opt for “hiding by flotsam mimicry” because their size makes them vulnerable to so many fish predators. Therefore, their slower swimming speed may be a consequence, rather than a cause, of that strategy.

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