BUOYANCY CONTROL IN DIVING BEHAVIOR OF THE LOGGERHEAD TURTLE, CARETTA-CARETTA

Neutral buoyancy at the stationary depth is advantageous for diving an imals. The adjustment of the air inspiration before diving can be a me chanism of buoyancy control for diving animals with lungs. The station ary depth of neutral buoyancy becomes deeper with larger inspiration. Our aim was to examine whether the loggerhead sea turtle, Caretta care tta regulates the buoyancy to be neutral at the stationary depth of th e dive. During an internesting period of the breeding season, we recor ded 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) fi rst descent, (2) gradual ascent (stationary period), and (3) final asc ent. In the gradual ascent phase, the turtle stayed at a certain depth without swimming. This means that the turtle was neutrally buoyant du ring the gradual ascent phase. The depth of the gradual ascent phase w as positively correlated with the dive duration, supporting the hypoth esis that neutral buoyancy of the loggerhead turtle is achieved by the air in their lungs.