It’s common for conservationists to shade the nests of sea turtles in an effort to increase the survival rate of hatchlings, but a new study finds that the practice could actually undermine the reptiles’ long-term population size if not carefully monitored.

Building shade structures over the nests of leatherback turtles, Dermochelys coriacea, at hatcheries on tropical and subtropical beaches has been shown to raise survival rates among hatchlings. However, the practice also alters the sex ratio of egg clutches; higher temperatures produce a greater proportion of females.

Some conservationists have favored the intervention, reflecting an assumption that saving more hatchlings and reducing the tendency toward female bias in hatchling sex ratios will boost leatherback numbers, according to an article co-authored by Professor Emeritus James R. Spotila of the Department of Biodiversity, Earth and Environmental Science.

The researchers noted, however, that female-biased primary sex ratios appear to occur naturally at most nesting beaches, and they concluded that reducing female biases could harm efforts to sustain leatherback turtles’ numbers.

TOO_COOL?

Models of sea turtle clutches in Costa Rica showed that shading the nests would have an undesirable impact on turtle populations in the long term.

Spotila published the study in Biological Conservation with co-authors Pilar Tomillo Santidrián of the Institut Mediterrani d’Estudis Avançats; Bryan P. Wallace of Ecolibrium; Frank V. Paladino of Purdue University, and Meritxell Genovart of the Centro de Estudios Avanzados de Blanes.

The team examined data from leatherback turtles nesting at Playa Grande, Costa Rica, where populations have declined.

Modeling revealed that decreasing nest temperatures under many scenarios would produce short-term increases in hatchling rates but a long-term decline in the number of nesting females and in total population size.

The researchers concluded that shading would be beneficial only if mean nest temperatures rise more than 2 degrees Celsius, as in a climate change scenario. In that event, extreme female biases could result in non-fertilized eggs and high embryo and hatchling mortality.

Their study also confirmed that altering sex ratios by producing more males in hatcheries could be detrimental for sea turtle conservation.