Productive foraging grounds enhance maternal condition and offspring quality in a capital breeding species.

Feeding ecology is an essential component of an organism's life, but foraging comes with risks and energetic costs. Species in which populations exhibit more than one feeding strategy, such as sea turtles, are good systems for investigating how feeding ecology impacts life-history traits, reproduction and carried over effects across generations. Here, we investigated how the feeding ecology of loggerhead sea turtles (Caretta caretta) nesting at the Cabo Verde archipelago correlates with reproductive outputs and offspring quality. We determined the feeding ecology of female turtles before and during the breeding season from stable isotope analysis of carbon and nitrogen and correlated isotopic ratio with female and offspring traits. We found that female turtles feeding at higher trophic positions produced larger clutches. We also found that females with higher δ13C values, typical of productive foraging areas, had greater fat reserves, were less likely to be infected by leech parasites and produced heavier offspring. The offspring of infected mothers with higher δ13C values performed best in crawling and self-righting trials than those of non-infected mothers with higher δ13C values. This study shows adult female loggerheads that exploit productive areas build capital reserves that impact their reproductive success and multiple proxies for offspring quality. Overall, our findings provide valuable insights into the complex interplay between feeding ecology and reproductive success, and reveal the transgenerational carry-over effects of both feeding ecology and health on offspring quality in sea turtles.

Changes in mean body size in an expanding population of a threatened species.

With some taxa, a reduction in the mean size of individuals may reflect over-harvesting and/or trophy hunting. However, we show that in sea turtles, a reduction in the mean size of breeding individuals may be part of the good news story of an expanding population. We describe a 70-fold increase in annual nest numbers on the island of Sal (Cape Verde, North Atlantic) between 2008 and 2020 (from 506 to 35 507 nests), making this now one of the largest loggerhead (Caretta caretta) nesting aggregations in the world. We use 20 128 measurements of the size of nesting turtles to show that their mean annual size has decreased by about 2.4 cm, from 83.2 to 80.8 cm. This decrease in the mean size of nesting turtles was not caused by the removal of larger turtles, for example by selective harvesting. Rather we develop a theoretical model to show than this decrease in mean size can be explained by an influx of first-time nesters, combined with a decrease in the size of those first-time nesters over time. A reduction in mean size of nesting turtles has been reported across the Atlantic, Pacific and Indian Oceans, and may be a common feature of population recoveries in sea turtles.