Journal of Ethology 15, 109-118,1997
Buoyancy control in diving behavior of the loggerhead turtle, Caretta caretta
Shingo Minamikawa, Yasuhiko Naito and Itaru Uchida
Neutral buoyancy at the stationary depth is advantageous for diving animals. The adjustment of air inspiration before diving can be a mechanism of buoancy control for diving animals with lungs. The stationary depth of neutral buoyancy becomes deeper with larger inspiration. Our aim was to examine whether the loggerhead sea turtle, Caretta caretta regulates the buoyancy to be neutral at the stationary depth of the dive. During an internesting period of the breeding season, we recorded the diving pattern of an adult female using a time-depth recorder and a time-swim distance recoder. The dives were classified into four types (Types 1 to 4) based on the time-depth profile. Types -3 and 4 (66% of the toral dive duration) have three phases in each dive; (1) first descent, (2) gradual ascent (stationary period) and, (3) final ascent. In the gradual ascent phase, the turtle stayed at a certain depth without swimming. This means that the turtle was neutral buoyant during the gradual asent phase. The depth of the gradual ascent phase was positively correlated with the dive duration, supporting the hypothesis that neutral buoyancy of the loggerhead turtle is achieved by the air in their lungs.
TU97-1
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