Trends in Reproductive Indicators of Green and Hawksbill Sea Turtles over a 30-Year Monitoring Period in the Southern Gulf of Mexico and Their Conservation Implications

SIMPLE SUMMARY: From 1990 to 2021, the number of hawksbill and green turtle nests has prominently increased thanks to the long-term protection of primary nesting sites in the Southern Gulf of México. However, despite not finding a statistical significance in the temporal trends, the size of nesting females, the clutch size, hatching, and emergence success are slowly decreasing in response to multiple conditions. Our study suggests that the protection efforts at nesting beaches show promising results. However, other ongoing natural and anthropic drivers are acting on sea turtle populations and their habitats and could dampen their recovery by reducing their reproductive output and hatchling production. Thus, because sea turtles are highly migratory animals moving between different countries, aside from protecting key nesting sites, restoring and monitoring crucial foraging habitats should be an immediate priority requiring international cooperation. ABSTRACT: Long-term monitoring programs of species at risk are efficacious tools to assess population changes, evaluate conservation strategies, and improve management practices to ensure populations reach levels at which they can fulfill their ecological roles. For sea turtles, annual nesting beach surveys are the most accessible method to estimating the population abundance and reproductive output, especially when these are done in primary nesting sites. However, little data exist on the long-term assessment of these parameters. Here, we present the trends of the nest abundance, female size, hatching, and emergence success of hawksbill (Eretmochelys imbricata) and green (Chelonia mydas) turtles at key nesting beaches in the southern Gulf of Mexico over 31 years (from 1990 to 2021). The nest abundance showed an increasing trend in both species as a result of the sustained protection and conservation effort, but there was no significant temporal trend in the annual female size, clutch size, hatching, and emergence success. However, these indicators showed decreasing mean values over the last decade and should be closely monitored. We suggest these decreases link to the combined effects of ocean warming and anthropogenic pressures affecting the sea turtle foraging grounds. Aside from protecting key nesting sites, protecting and restoring crucial foraging habitats should be an immediate priority requiring international cooperation.