Short-term gain, long-term loss: How a widely-used conservation tool could further threaten sea turtles

Abstract

Sea turtles nest on tropical and subtropical beaches, where developmental success of egg clutches depends on nest temperature. Higher nest temperatures increase embryo and hatchling mortalities and produce female hatchlings. Nest shading has been used on some beaches to reduce nest temperatures, and thereby increase number of hatchlings and reduce female-biased sex ratios. We modeled short- and long-term effects of reducing mean nest temperatures on a leatherback turtle (Dermochelys coriacea) population for which the effect of temperature on sex ratios and emergence success (# hatchlings emerged/ # eggs) is well-established. We simulated mean nest temperature reductions of −0.5 °C, −1 °C, −1.5 °C and −2 °C in relation to current mean (30.4 °C) and projected population responses over 100 years. Additionally, we run climate change simulations of +0.5 °C, +1.0 °C and +2.0 °C to assess if shading could be needed after passing a certain threshold.Emergence success increased with reduced nest temperatures. However, lowering nest temperatures ultimately caused long-term declines in number of nesting females and total population size, because the number of female hatchlings was reduced. Because hatcheries are a widely-used conservation tool, caution must be used to avoid reducing the number of female hatchlings by lowering nest temperatures. Nest cooling may only be needed under critically low hatchling production and extremely biased female sex ratios that we only found at +2.0 °C. If nest shading is to be used, it should be applied strategically to optimize hatchling production with natural sex ratios to achieve both short-term conservation goals and long-term population sustainability.