Incubation Temperatures and Metabolic Heating of Relocated and In Situ Loggerhead Sea Turtle (Caretta caretta) Nests at a Northern Rookery

Abstract

Miniature temperature loggers were used to better understand the incubation temperatures, patterns in metabolic heating, and potential implications for sex determination of relocated and in situ loggerhead sea turtle clutches near the northern extent of their nesting range. All sea turtles display temperature-dependent sex determination, with cooler nests producing males and warmer nests producing females. Analysis of the factors that affect incubation temperatures provides insight into variation in hatchling sex ratios over temporal and spatial scales and may help to guide management measures for the imperiled loggerhead sea turtle. Although no temperature difference was detected between relocated and in situ clutches during the thermal sensitive period, relocated nests hatched more quickly and incubated at warmer temperatures than in situ clutches for the entire incubation period. Metabolic heating was apparent in all clutches, beginning during the middle third of incubation, with the greatest gradient between nest temperature and surrounding sand temperatures (x ¯ = 1.5 ± 0.05°C) that occur during the final third of incubation. The magnitude of metabolic heating was not different between relocated and in situ clutches. Diel temperature fluctuations within nests were significantly less pronounced than in adjacent sand, which implies a degree of thermal buffering within the nest chamber. During the thermosensitive period, all nests incubated at a mean temperature above that of the estimated pivotal temperature (29.2°C), which implies a strongly female-biased hatchling sex ratio during the portion of the nesting season monitored. Potential impacts on incubation temperature and resultant sex ratios should be considered and explored on a beach-by-beach basis before adopting nest relocation as a conservation measure.