Foraging niche segregation between juvenile and adult hawksbill turtles (Eretmochelys imbricata) at Príncipe island, West Africa

Abstract Hawksbill sea turtles are the most tropical sea turtle species with one of the last remaining aggregations in West Africa found on Principe Island (1° 37′ N; 7° 23′ E). Here we present for the first time, data on the trophic and foraging ecology of both juvenile and adult hawksbill turtles found in the shallow waters of Principe, using stable isotope analyses of carbon (δ 13 C) and nitrogen (δ 15 N), and assess any isotopic niche segregation between these two life-stages. Hawksbill turtles were sampled from December 2012 to June 2014, complementary to a snorkeling survey conducted around the entire coastline ( ca . 100 km). δ 13 C and δ 15 N values were measured in epidermal samples of 40 individuals and analyzed in the context of isotopic niche width and overlap (i.e. trophic and foraging niches). Juveniles hawksbills (n = 29;  75 cm), especially in relation to δ 13 C values (i.e. habitat use) but also in δ 15 N values (i.e. trophic level). Variances between adults and juveniles were not homogenous for both isotopes and larger for adults, particularly for δ 13 C values. We found significant differences in δ 13 C values between the two groups, but not for δ 15 N, and a significant correlation between δ 13 C values and CCL for the pooled data. SIBER (stable isotopes Bayesian ellipses in R) outcomes support these results and, although niches are not completely segregated, it indicates spatial foraging segregation between juveniles and adults. The fact that Principe Island's shallow waters are constantly being patrolled by spearfishermen, together with the existence of a large insular platform and a superior dive capacity in larger hawksbills, might influence this segregation. Our results suggest that part of the adults may be originating from isotopically distinct areas. To have a better understanding on the distribution and abundance of the sea turtle populations in Principe, including their connectivity with other foraging and breeding areas, future in-water studies focused mainly on the entire insular platform of Principe, but also on the adjacent probable foraging areas of the Gulf of Guinea, are required.