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Marine Turtle Newsletter 26:10-11, © 1983

A Method for Reducing Movement-Induced Mortality in Turtle Eggs

J.D. Miller¹ and C.J. Limpus^2
1Department of Zoology, University of New England, Armidale, N.S.W., 2351 Australia
²Queensland National Parks and Wildlife Service, Pallarenda, Townsville, QLD, 4810 Australia

The problem of movement-induced mortality (Limpus et al., 1979) must be considered in any conservation effort in which eggs are moved. Eggs can be moved immediately after oviposition (or within 3 h) without danger, but movement after about 10 h reduces hatching success (Limpus et al., 1979). The more severe the handling or the longer the interval between oviposition and movement, the greater the egg mortality. Because low temperatures slow or suspend development in turtles, loggerhead turtle eggs were subjected to artificially low temperatures to test the hypothesis that short-term cold exposure could be used to reduce movement-induced mortality.

Eggs were grouped into treatments (low temperatures 10°, 14°C; warm temperatures 24.5°, 27.5°, 29°C), within 1 h of oviposition at Mon Repos beach (25°S, 152°E) Queensland, Australia. The methods of incubation followed those used by Miller and Limpus (1981). Groups of 10 eggs from each treatment were inverted axially 180° at 24 h intervals (24, 48, 72, 96 h) and placed at 29°C until hatching. Other groups of 10 eggs were subjected to 10°C for the same intervals then moved to 29°C but were not inverted. The 29°C incubation temperature was chosen because it approximates the temperature about which sand temperatures at nest depth at Mon Repos fluctuate through most of the nesting season. In addition, 29°C is within the range that gives high hatching success in constant temperature incubation experiments (Limpus et al., 1983). Hatching success (sensu Miller and Limpus, 1981) of undisturbed clutches laid on Mon Repos was 83.8% (Limpus et al., 1979). Experimental hatching results were compared against this value using Chi-squared tests with Yates correction for continuity.

Eggs incubated at the warmer temperatures (29°, 27.5°, 24.5°C) prior to inversion exhibited significantly lower hatching success than those incubated at 14 and 10°C prior to inversion (Table 1).

Table 1. Percent hatching success of eggs incubated at 29°C following initial cooling and inversion at specific time intervals (control group not inverted). Number of eggs in trial in brackets. X² test: * = significant P<0.05, NS = not significant.

At 24 h, the effect of inversion on survival was reduced with each decrease in temperature until no significant difference occurred between the observed and expected values. Inversion of eggs at 48 h killed all but 2 eggs among those incubated at 29°, 27.5° and 24.5°C and no eggs survived inversion after 72 h at these warm temperatures. Although hatching success of eggs incubated at 14° prior to inversion was higher than that of eggs incubated at the warmer temperatures for the same interval, the results were significantly different from the control value. Rotation of the eggs incubated at 10°C for 24, 48 and 72 h did not cause significant mortality, however the hatching success of eggs incubated at 10°C for 96 h before inversion was significantly different from the expected success of 83.8%. The hatching success of eggs incubated under the same conditions but not inverted was consistently high. Taken together, these results strongly indicate that movement-induced mortality during the first 72 h of incubation can be reduced by decreasing the temperature to 10-14°C.

By using low temperatures to inhibit movement-induced mortality, it is possible to move a clutch of turtle eggs from a remote rookery to distant laboratories with relative impunity. This should allow more sophisticated studies of the biology of the eggs than is usually possible at many beaches. The large scale movement of turtle eggs to hatcheries for conservation is a common practice even though rough handling or delay reduced hatching success. The cooling of eggs immediately following laying to 10-14°C may have some application towards increasing hatching success in those conservation efforts in which the eggs cannot be reburied into the hatchery within 2 h of being laid.

Limpus, C.J., Baker, V. and Miller, J.D. (1979). Movement induced mortality of loggerhead eggs. Herpetologica 35(4), 335-338.

Limpus, C.J., Reed, P. and Miller, J.D. (1983). Islands and turtles. 'The influence of choice of nesting beach on sex ratio. In "Proceedings: Inaugural Great Barrier Reef Conference." (J.T. Baker, R.M. Carter, P.W. Sammarco and K.P. Stark, eds). James Cook University Press Townsville, Aust., 397-402.

Miller, J.D. and Limpus, C.J. (1981). Incubation period and sexual differentiation in the green turtle, Chelonia mydas L. In Proc. of Melbourne Herp. Symp. (C. Banks and A. Martin, eds). The Royal Melbourne Zoological Gardens, Melbourne, 66-77.