Assessing Sea Turtle Population Trends Given Strong Environmental Forcing

The causes of marine turtle population variability are poorly known, frustrating scientists and managers. Regional climate indicators explain some of the large annual fluctuations in turtle surveys, but decadal or longer-term trends are considered the result of anthropogenic pressures. Here we use basin-scale climate indices and regional surface temperatures to estimate loggerhead turtle nesting trends at a variety of spatial and temporal scales. Unlike previous studies, our models anticipate that oceanographic features regulate juvenile recruitment. We find nesting fluctuations are regionally synchronous and are strongly correlated to decadal climate oscillations; explaining 49-66% of the annual variability in the Atlantic and Pacific populations and capturing both the annual and decadal nesting trends. Our models suggest an environmental role in the observed declines since 1950 and predict continued losses in the coming decades. These results do not exonerate anthropogenic impacts, but highlight the importance of climate to juvenile recruitment in marine organisms.