Conservation measures for marine turtles include incubating wild-laid eggs in styrofoam boxes (housed above-ground in hatcheries protected from predation) which gives high hatch success. However, incubation time using this method is often longer than in natural nests (especially so for leatherback turtle Dermochelys coriacea eggs) reflecting lower temperatures. Incubation temperature affects sexual differentiation, with lower temperatures producing more males. The use of styrofoam boxes for incubation of leatherback eggs and effect on hatchling sex ratio was investigated at Wia-Wia Reserve, Surinam.
In 1982, leatherback eggs were taken from 10 clutches (five clutches laid in May and incubated during the rainy season between May and June; five at the end of June incubated during the warmer, drier period between July-August) that would have been destroyed by high tides. These were incubated in styrofoam boxes (following methods described by Schulz 1975). About 45 eggs (from the same clutch) were put in each box. Upon emergence, 10 hatchlings were randomly selected from each box for sexing (requiring dissection). Also included in the analysis were samples of hatchlings sexed from five boxes from clutches laid 17 March - 2 April 1980.
For comparison, 10 hatchlings were sexed from each of six clutches incubated in natural beach nests laid in May, and from five laid at the end of June, 1982. Samples of sexed hatchlings from two naturally incubated clutches in 1980 were also included in the analysis.
Eggs from several ‘doomed’ clutches were excavated and reburied in hand-dug holes similar to natural nests. Ten hatchlings were sampled from each of two clutches laid on 30/31 July 1982.
Temperatures within the boxes and beach nests were monitored through incubation.
Incubation to hatching in the styrofoam boxes averaged: 73 days for May 1982 laid clutches; 70 days for June 1982 clutches; and 72 days for the 1980 clutches. For natural nests the average was 66 days for May nests and 61 days for June nests (likewise reburied nests, 60-61 days).
There was a marked male sex ratio bias of hatchlings from box-incubated eggs; no females were recorded during either two (of the thermally different) seasons. Natural ratios varied seasonally, averaging 30% females in May laid clutches and 100% female in June laid clutches (reburied clutches produced a similar sex ratio). These results appear correlated with the boxes being 1.4–2.4°C cooler than the sand.
The male-biased sex ratio is consistent with the well-known effects of temperature on sexual differentiation and verifies concerns about styrofoam box use for incubation of sea turtle eggs. The bias was much larger than that reported for green turtles Chelonia mydas.
Schulz J.P. (1975) Sea turtles nesting in Surinam. Zool. Verh., 143, 1-143.
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