The effects of warming on loggerhead turtle nesting counts

Global trends in marine turtle nesting numbers vary by region, influenced
by environmental or anthropogenic factors. Our study investigates the
potential role of past temperature fluctuations on these trends,
particularly whether warmer beaches are linked to increased nesting due to
higher female production (since sea turtles have temperature-dependent sex
determination). We selected the loggerhead turtle (Caretta caretta) due to
its wide distribution, strong philopatry, and vulnerability to
environmental changes. We compiled nest counts per year on 35 globally
significant rookeries, analysing trends at regional and individual beach
levels. We compiled air (CHELSA) and land surface (MODIS) temperature
datasets spanning the last four decades (1979-2023) for each location. To
analyse temporal trends in nest counts and temperatures, we used
generalised additive models and Mann-Kendall trend tests. Additionally, we
correlated nest counts with lagged air temperature variables. We found
significant warming at 33 nesting locations, 23 of which also showed
significant increases in nest counts. Our results suggest that rising
temperatures may be boosting nest numbers in regions of the Caribbean,
Atlantic Ocean, and Mediterranean (sites in Cayman, Mexico, Brazil,
Cyprus, and Turkey). Furthermore, while some regions temporarily benefit,
continued warming could precipitate long-term population declines. This
regional variability helps predict species responses to climate change,
with the general global increase in nest counts already indicating
short-term warming effects. Nesting count trends might reflect a
combination of natural ecological phenomena, conservation efforts, and
warming effects. Long-term studies are needed to assess global trends in
the sex ratio of hatchlings and the extent to which feminisation is
driving nest numbers.