Circadian Rhythm on Diving Motion of the Loggerhead Turtle Caretta caretta during Inter-nesting and its Fluctuations Induced by the Oceanic Environmental Events

Abstract

A continuous diving recorder and a swimming distance recorder were used to monitor the diving performances and swimming behavior of the free-ranging loggerhead turtle Caretta caretta during her inter-nesting periods. A clear circadian rhythm was found on her diving frequencies and durations in off shore swimming performances while it was obscure at the period during which she swam near coastal area. The circadian rhythm was closely correlated with the sunrise and the sunset. However, this was disturbed by irregular environmental events such as typhoons and when passing through frontal zone. The rhythm was considerably higher when she arrived at coastal zone, It corresponded to the tidal period.