Buoyancy control in diving behavior of the loggerhead turtle,Caretta caretta |
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Authors: | Shingo Minamikawa Yasuhiko Naito Itaru Uchida |
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Institution: | (1) Department of Zoology, Graduate School of Science, Kyoto University, 606-01 Sakyo, Kyoto, Japan;(2) National Institute of Polar Research, Kaga, Itabashi, 173 Tokyo, Japan;(3) Port of Nagoya Public Aquarium, 455 Minato, Nagoya, Japan |
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Abstract: | Neutral buoyancy at the stationary depth is advantageous for diving animals. The adjustment of the air inspiration before
diving can be a mechanism of buoyancy 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 recorder. The dives
were classified into four types (Types 1 to 4) based on the time-depth profile. Types-3 and 4 (66% of the total 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 neutrally buoyant during
the gradual ascent 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. |
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