Neglecting cooler low-season nest protection could deprive sea turtle populations of valuable hatchlings

Reproductive seasonality is present across species and phyla. Many species retain seasonal patterns even in tropical regions where climatic variations may be less apparent. Environmental features and large-scale environmental cues play a role in species seasonality and can have major effects on reproductive success. In organisms that present environmental sex determination, the season in which individuals reproduce has consequences for their primary sex ratio. Here we looked at the possible effects on fitness and primary sex ratio for the olive ridley sea turtle (Lepidochelys olivacea) when nesting during peak and low nesting seasons. In the eastern Pacific, peak olive ridley sea turtle nesting occurs during the warmest months, which coincide with the rainy season. Yet, as nesting takes place year-round, a small proportion of the nests laid during the dry part of the season are exposed to contrasting environmental conditions. Most of the studies on Pacific coast sea turtles have estimated sex ratios produced during the rainy, high abundance period when most conservation activities are focused. Thus, dry-low season nests have on the whole, been overlooked. Here we compared sex ratios and hatchling fitness for offspring produced during the dry and rainy seasons in 2015. We found that olive ridley clutches incubated during the dry-low season were exposed to lower temperatures, yielded higher hatchling success, mainly produced male offspring and larger, heavier hatchlings with better locomotor abilities. This highlights that, for sea turtles, protecting nests outside of the peak nesting season may help future population viability by yielding higher proportions of males with greater locomotor capacities and, thus, survival. Our results highlight the critical value of monitoring and protecting species during their entire reproductive period and not concentrating all resources on the peak season to collect more data and protect a greater number of organisms. Our results suggest that monitoring low-season reproductive effort (nests in this case), albeit at much lower densities, would be critical for understanding and possibly ensuring population viability and adaptation to contemporary climate change and anthropogenic threats.