Propulsive force generated by flipper beat of sea turtles

Abstract

Propulsive force generated by flipper beat of sea turtles was evaluated to confirm the design adequacy of a flap door covering the outlet in a sea turtle releasing device (TRD) for large-scale set nets. The force generated by flipper beat was measured by a tension meter using nine green turtles (SSCL: 0.39-0.72 m) and four loggerhead turtles (0.63-0.84 m) in a water tank (10 m × 10 m × 2.1 m depth). Video recording was simultaneously conducted and time-series data of flipper beats were obtained. Sea turtles alternated a set of flipper beats with a rest. The average of peak force values and flipper beat frequencies in a set of flipper beats decreased in order of each set for both species. Both the force and beat frequency of green turtles were twice as large as those of loggerhead turtles, and the impulse values of a single beat were similar between the two species. There was a strong linear relationship between peak force value and turtle body size in the first set, but there was no significant relationship after thirty minutes later for both species. Even after 30 minutes and later, the generated force was still large (> 40 N) enough to open the flap door of the current TRD.