Feeding ecology of the olive ridley turtle (Lepidochelys olivacea) in southern Brazil

The olive ridley turtle (Lepidochelys olivacea) is the least studied sea turtle species, despite being the most abundant. Few studies on its diet have been reported worldwide, which suggest an omnivorous diet. The objective of this study was to characterize ontogenetic changes in diet composition and habitat use of the species in southern Brazil using gastrointestinal tract (GIT) contents and stable isotope (δ13C and δ15N) analyses. GITs (n = 10) and skin (n = 34) samples from specimens found stranded on the coast of Rio Grande do Sul (RS; from 31° 20′ S–51° 05′ W to 33° 45′ S–53° 22′ W) and individuals from incidental captures in the local bottom pair trawl fishery were collected from 2014 to 2019. Eighteen food items were found in the GITs, where the hermit crab Loxopagurus loxochelis had the highest contribution to the species diet, followed by the gastropod Buccinanops monilifer and the crabs Hepatus pudibundus and Libinia spinosa. Stable isotope mixing models showed the hermit crab as the most assimilated prey to juvenile and adult individuals, followed by a small contribution of salps to juvenile specimens. Prey preferences indicate a predominant use of the neritic environment for adults and a use of both neritic and oceanic environments for juvenile individuals. These results demonstrated that juvenile and adult olive ridley turtles use the coast of RS as a feeding ground; therefore, this area should be considered when proposing conservation measures for the species.