The impacts of extreme El Niño events on sea turtle nesting populations
The El Niño Southern Oscillation (ENSO) is the predominant interannual pattern of climate variability in the world and may become extreme approximately once every 20 years. Climate-forced interannual variability in fecundity rates of long-lived species are well-studied, but the effect of extreme events is less clear. Here, we analyzed the effect of the extreme 2015–16 El Niño event on three long-lived sea turtle species in a region highly influenced by ENSO. The effect of this extreme event varied considerably among species. While reproductive success dramatically declined in leatherback turtles (Dermochelys coriacea), the reduction was only marginal in green turtles (Chelonia mydas). Nevertheless, the number of nesting green turtles decreased following the extreme El Niño event, likely due to decreased ocean productivity. We used global climate models to project an increase in the decadal occurrence of extreme events from ~ 0.7 events (beginning of twentieth century) to ~ 2.9 events per decade (end of twenty-first century). This resulted in a projected decline in the reproductive success of leatherback turtles (~ 19%), a milder decline in olive ridley turtles (Lepidochelys olivacea) (~ 7%), and no decline in green turtles (~ 1%). Extreme El Niño events can have a strong detrimental effect on East Pacific leatherback turtles, a population that is already critically endangered due to other anthropogenic impacts. Our results highlight the importance of conducting species-specific and site-specific analyses of climatic impacts on sea turtles.
KeywordsENSO Extreme events Long-lived Sea turtles Reproductive success Climate change
We thank all field coordinators, assistants, and volunteers that contributed to the data collection over the years at the various projects. We thank the Ministry of Environment and Energy of Costa Rica for providing research permits and Roger Blanco and Roberto Zúñiga for facilitating the process.
PST, LGF, MW, NT and NJR discussed the implications of the extreme 2015–16 El Niño event in Costa Rica and conceived the study. PST, NJR and FVP led and provided data for the projects at Cabuyal and Playa Grande, LGF led and provided data for the projects at Nancite and Isla San José, MW and NT led and provided data for Punta Pargos and CMO led and provided data for Ostional. VSS advised and assisted with the projections of extreme events. PST wrote the manuscript with input from all authors.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
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