SREL Reprint #2072

Possible demographic and ecologic consequences of sex ratio manipulation in turtles

Jeffrey E. Lovich

National Biological Service, Midcontinent Ecological Science Center, Palm Springs Field Station, 63500 Garnet Avenue, North Palm Springs, California 92258-2000 USA

Summary: Vogt (1994) performed a valuable service to the chelonian conservation community by initiating a dialogue on the merits of using sex ratio manipulation as a conservation tool. In the spirit of continuing that dialogue I maintain that there is insufficient information at this time to evaluate fully the potential impact of sex ratio manipulation on turtle population persistence and that the information available argues against manipulation. Furthermore, Vogt's suggestion to produce predominantly female turtles would only exacerbate problems caused by predicted global warming which has the potential to eliminate the production of male offspring in some turtle species (Janzen, 1994).
The pitfalls of sex ratio manipulation in turtle populations were first highlighted by Morreale et al. (1982) who warned that artificial incubation projects for green seaturtles (Chelonia mydas) were releasing all male, all female, or even intersex hatchlings. They recommended against the use of artificial incubation in an effort to maintain natural sex ratios. Later, Frazer (1992) eloquently articulated the fallacy of headstarting as another conservation technique that emphasizes treating symptoms instead of causes. Too many conservationists had defined the disappearance of turtles only numerically in terms of there not being enough turtles. The "halfway technology" solution, as discussed by Frazer (1992), was simply to produce more turtles without focusing attention on causes for their disappearance. This theme was amplified by Meffe (1992) who noted the propensity of humans to embrace technology in the search for solutions to ecological problems, again focusing on symptoms and not causes.
The idea of using sex ratio manipulation to "jump-start" declining turtle populations has all the allure of technology noted by Meffe combined with the short-sightedness of the halfway approach noted by Frazer. Now the problem appears to be not just having too few turtles, but not having enough female turtles. In a world that is increasingly hostile to turtles of both sexes, I see little hope for this approach until we face the real problems of over-exploitation, pollution, habitat destruction, and rampant human population growth (Meffe et al., 1993).

SREL Reprint #2072

Lovich, J.E. 1996. Possible demographic and ecologic consequences of sex ratio manipulation in turtles. Chelonian Conservation and Biology 2:114-117.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).