Inferring gestational diet in free-ranging Greater Caribbean manatee (Trichechus manatus manatus) using newborn hair isotopic signatures

Abstract

Species feeding habits can be accessed in a variety of ways, such as fecal samples and stomach contents. However, these methods reflect only the individual’s recent diet, disregarding a broader perspective of feeding habits along a temporal scale. Such differences can be evaluated by analyzing inert biological samples, like hair and skin tissues, which absorb and preserve isotopic signatures over time. In this study we analyzed hair samples from nine stranded manatee calves, in order to trace their mothers’ diet during gestation, an innovative attempt for this species which is currently classified as Critically Endangered of extinction in Brazil. Our sample, however small, contained data distributed along four Brazilian states, covering half of the current occurrence area of the species in the Brazilian coast. δ¹³C values showed variability among calves, particularly in individuals aged 0.9 - 1.5 months. In contrast δ¹⁵N values, carbon and nitrogen concentrations presented very similar values, regardless of calf age. δ¹³C values had a strong positive correlation with size at stranding even when controlled by age, suggesting that enriched δ¹³C signatures correspond to the production of larger calves. Despite our small sample size, here we present a substantial contribution to the knowledge of the diet of free-ranging females, use of habitat during pregnancy and how it varies according to resource availability. Furthermore, our findings support the hypothesis that nutritional intake during gestation periods might have a long-term impact on calf growth and development.