How many years do sea turtles have to shift their phenology due to global warming?

Sea turtles are among the marine life endangered by human activities that directly disturb their environment, such as fisheries bycatch, habitat degradation, and pollution. Additionally, the effects of ongoing global warming can also pose an extra threat since sea turtles are a species with temperature-dependent sex determination. Hence, with the increasing temperatures, they may experience a feminization phenomenon that can pose a risk to their extinction. Since the female sea turtles exhibit a great fidelity to beach sites where they were nested, a potential behavioral change to mitigate the effects of global warming is a nesting phenological shift to cooler periods of the year. Based on previous observations, the most optimistic phenological shift for sea turtles can be extrapolated to 27 days (about one month) per 1.5°C increase in the nesting sand temperature. Using this hypothesis, in this study, we aim to assess by when the sea turtles have to perform a one-month phenological shift in 48 sites around the world and the respective warming mitigation achieved by the phenological shift. We used two future climate scenarios (SSP2-4.5 and SSP5-8.5) from the simulations of 22 CMIP6 climate models. For SSP2-4.5 future scenario (a moderate scenario), it is projected that the middle of this century is the earliest date for phenological shift in sites located in the southeastern part of the USA and in the eastern Mediterranean sites.  Sea turtles nesting in the equatorial sites have up to the end of the century or beyond to perform a phenological shift. However, the warming mitigation is greater in sites located further away from the equatorial region, whereas the sites in the equatorial region show a small mitigation effect from the phenological shift. Regarding the SSP5-8.5 future scenario (an extreme scenario), the phenological shift has to be performed in this century in all sites, with some sites in the Mediterranean with threshold dates sooner than mid-21th century. Moreover, compared with the SSP2-4.5 future scenario, there is some reduction in warming mitigation capacity, but it is not significantly different from the moderate scenario. Considering the uncertainty from the climate models' projections, our analysis shows that the models have lower uncertainty in sites projecting earlier threshold dates for phenological shifts.