Seawater irrigation on nests can increase male marine turtle production

Abstract

Global warming is increasing marine turtle nesting beach sand temperatures throughout the world. All marine turtles have temperature-dependent sex determination, with female hatchlings produced at warmer incubation temperatures. These warmer sand temperatures are causing a scarcity of male hatchlings at many nesting beaches. A range of mitigation strategies including shading and freshwater irrigation are being trialled at marine turtle nesting beaches around the world to address this issue. Because seawater is always abundant at marine turtle nesting beaches, we trialled a number of intense, one-off seawater irrigation experiments (equivalent to 100 and 200 mm rainfall) to test if male green turtle Chelonia mydas hatchling production could be increased without decreasing overall hatching success at Heron Island, southern Great Barrier Reef, Australia. We found that different combinations of seawater volume and temperature could produce a short-term drop in nest temperature by 2°C. When applied during the middle of embryonic development, these irrigation treatments could increase the proportion of male hatchlings compared to non-irrigated control nests, with less than a 10% decrease in hatching success. Hence, seawater irrigation has the potential to be a viable management strategy to increase the proportion of male marine turtle hatchlings at beaches that produce all, or nearly all, female hatchlings.