Issue_2_09

Hazel K, Lawler IR, Hamann M (2009)
First published in Journal of Experimental Marine Biology and Ecology 371: 84-92

Green turtles Chelonia mydas of immature and adult size (n=19, curved carapace length 49 to 118cm) were equipped with time-depth recorders for short periods (=7 d) to investigate diel and seasonal variation in diving behaviour. Research sessions were distributed over 2 years to cover seasonal variation in sea temperature from 14°C to 30°C.

Diurnal diver were shallower and shorter than nocturnal dives, with diel patterns also evident in dawn and dusk peaks in occupation of depths within 1m of the surface, elevated diurnal occupation of depths 1 to 2 m below the surface and elevated nocturnal occupation of depths >2m.

Dive duration increased as sea temperature decreased, showing strong negative correlation by day and by night. Study turtles made resting dives that were 3 to 4 times longer in median duration, and six times longer in maximum duration, at cool temperatures than they were at warm temperatures, but there was no evidence of winter diapaus or location shift to avoid cold water.

The large majority of turtles spent 89 to 100% of their time at depths =5 m below the surface, three individuals did not exceed 3m and the maximum depth recorded by any turtle was 7,9 m, although deeper water was available.

Furthermore, the dive data indicated that study turtles collectively spent more than 80% of their time at charted (low tide) depths of 3 m or less, indicating that they consistently used the shallow margins of the bay where human activities tend to be concentrated, therby potentially increasing their exposure to anthropogenic threats.

[The study was conducted in Moreton Bay, on the east coast of Australia using Star-Oddi DSTs.
The whole article can be viewed at http://dx.doi.org/10.1016/j.jembe.2009.01.007]

Green turtle distribution. Red circles represent major nesting locations, yellow circles represent minor nesting locations.