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Marine Turtle Newsletter 19:1-2, © 1981

Editorial

Nicholas Mrosovsky

This issue presents articles on how head-starting turtles might be evaluated. The question asked in previous editorials (Marine Turtle Newsletter Nos. 15 & 16, 1980) was not whether head-starting was effective or undesirable but how it might be possible to learn the truth of the matter. We hope that the thoughtful replies given will interest those undertaking or contemplating head-starting.

Ideally, however, to be maximally valuable, debate should anticipate conservation experiments. Another experiment that might soon be tried ... and therefore merits scrutiny now ... is the warming-up of eggs to produce more females. Since 1978, when the likelihood that artificial incubation methods affect sex ratio was aired in the Marine Turtle Newsletter (Editorial, 1978, No. 9, 1-2), much has been learned. Methods of sexing hatchlinqs have been found, sexual differentiation of loggerhead and green turtles has been shown to be temperature dependent, the critical period within incubation has been determined; it has been demonstrated that styrofoam box incubation can bias sex ratio towards males, a team project on ridley and green turtles in Costa Rica is looking at many other variables and there has also been work on the subject in Australia, Surinam, Mexico, the USA and the Cayman Turtle Farm. Papers will be listed in the newsletter as they appear. Ongoing studies on more rapidly maturing reptiles will soon resolve the question of whether temperature affects on sexual differentiation last through to breeding. It will be much harder with sea turtles to learn if sex at hatching predicts sex in the adult but given thc available data (see Bull, J.J. 1980, Quart. Rev. Biol. 55, 3-21; Nrosovsky, N., 1980, Amer. Zool. 20, 531-547), the onus of proof is on those who argue otherwise. Has anyone seen a turtle change sex?

Assuming then that having an ovary hatching means laying eggs later on, there may be attractions in producing more females in places where turtles are exploited for their eggs, Malaysia and Surinam for example. Farms have more cows than bulls, more hens than roosters, so why not more female turtles?

One worry is our ignorance of population structure, of the biology of turtles in general. Who would have thought ten years later that incubating eggs in styrofoam boxes affect sex ratio? Nevertheless head-starting had been launched despite the many unknowns, so why not feminizing also? Before that is tried it might be useful not merely to insist on our ignorance of the consequences, but to have specific formulations of the unknowns and dangers. The aim should not be to stop legitimate experiment but to influence it to be as meaningful as possible. Would it be possible to design a limited experiment in an informative way? The Marine Turtle Newsletter would appreciate short articles and the views of readers on the question of deliberately feminizing turtles during incubation.