Preliminary result of ontogenetic change of wave orientation of green turtles in the initial growth stages

Abstract

Head-starting is the practice of growing hatchlings in captivity to protect them from the high rates of natural predation that would occur in their early stage. It is concern whether the head-started turtles disperse to the open sea after the release like wild turtles. During offshore migration, hatchlings use refracted wave as an orientation cue to go straight to the open sea. This conditioned response to the wave results in movement away from land towards the open sea, because waves and swells entering shallow coastal areas are refracted until they approach a beach directly. Therefore, it is considered that the ability of orientation to the wave is an important key for their efficient migration. In order to investigate the growth stages, in which hatchlings keep their willingness to orientate toward the direction of surface wave approach, we conducted a preliminarily wave tank experiment using green turtle (Chelonia mydas) in their initial growth stages. The results of the preliminary experiment indicated that the green turtle keep the response to the wave until 2 weeks of age. We need to continue the experiment hereafter.