Sea Turtle Ocean Finding Behaviour

Limpus, Colin

Mrosovsky (1967) favors hatchling sea turtles being directed to the ocean by a brightness differential existing between seaward and landward horizons which is constant in orientation. Carr ( 1967) suggests that some 'quality of the light out towards the sea' leads the hatchlings seawards. These views are based on work with Green Turtles Chelonia mydas. Current opinion regards light as providing the directional cues enabling all species of sea turtles to find the ocean. The present study suggests that topography of the surrounding horizon line provides a more important cue to ocean finding and that sea turtles orient to a combination of cues from the topography of the horizon line and light intensity. Results are presented from three separate lines of investigation. (a) Several thousand nestings and subsequent emergences of Loggerhead turtles Caretta caretta at Mon Repos (approx. 25°S) in south-east Queensland, Australia, were examined for conditions under which turtles tailed to locate the ocean under natural conditions. (b) Several hundred groups of hatchlings were collected on emergence and released at selected points within the nesting area under various weather conditions and at different times of the day. Their subsequent behavior was observed. (c) Groups of forty hatchlings were released from the center of a six feet (183 cm) diameter timber floored arena (Fig. 1). The wall was one foot (30.5 cm) high dark brown unpainted hardboard. Eight inches (20.5 em) inside the wall were twelve pockets into which the wan· dering hatchlings could fall. Each pocket collected from a 30° arc. The arena, sited in the nesting area, was supported from beneath. Unless otherwise stated, the horizon line seen by the hatchlings was that of the wall and gaps of varying height which could be made in the wall. Each gap spanned one pocket (30° arc). Painted boards to full wall height, each spanning a 30° arc, were placed inside the wall for some trials. The arena floor was kept horizontal and the whole unit could be rotated through 360°. Trials were run when there appeared to be uniform illumination of the inside walls of the arena. Since no suitable light meter was available for these experiments, subjective judgments had to be made on light intensity.

Sea Turtle Ocean Finding Behaviour

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