Metabolic organization of pregnant freshwater stingray and their offspring.

The elucidation of energetic patterns in adult viviparous elasmobranchs and their offspring can contribute to understanding ecophysiological questions, such as maternal-fetal metabolism and group life-history traits. We characterized the energetic substrates in pregnant individuals and stages of offspring development in the freshwater stingray Potamotrygon amandae. Our results show that the energetic distribution of the yolk is composed of more lipids than proteins, whereas the inverse pattern is observed in the egg and uterus, proving the plasticity of the energy provision of the species. As a novelty, we describe that yolk/intestine transfer occurs in this species.

Effects of biological traits on capture-induced parturition in a freshwater stingray and perspectives for species management.

Elasmobranchs are particularly vulnerable to overexploitation and population depletion, especially due to their life-history traits, such as low reproductive output and slow growth. Given that capture-induced parturition (abortion or premature birth) is a common consequence of fisheries in elasmobranchs, but still little studied, we investigated how the abortion/premature birth process varies in response to reproductive traits in a freshwater stingray, Potamotrygon amandae. Our results revealed that capture-induced parturition was affected by reproductive traits, such as litter size (one to seven) and gestation stage. The event occurred faster in pregnant females with high litter size during late pregnancy. Also, as found in other elasmobranchs, litter size was positively correlated with maternal size. These findings indicate that larger pregnant females in late pregnancy are more vulnerable to capture-induced parturition. This study improves our understanding of the capture-induced parturition process in stingrays, and provides useful information for management strategies and future recommendations for elasmobranch conservation.

Resource partitioning between two young-of-year cownose rays Rhinoptera bonasus and R. brasiliensis within a communal nursery inferred by trophic biomarkers.

Although interspecific trophic interactions plays a principal role within elasmobranch communal nurseries, little is known over variation in foraging strategies adopted by young-of-year of sympatric species. To test the hypothesis of dietary resource partitioning between batoids within a communal nursery, we investigated two cownose ray species, Rhinoptera bonasus and R. brasiliensis, which occur in heterospecific groups, a strategy predicted to increase survival and foraging success. Using two biochemical tracers, fatty acids (FA) and stable isotopes (δ15 N and δ13 C), the combined effects of maternal investment and the formation of heterospecific groups implying competition for, or partitioning of available food resources were investigated. Through univariate and multivariate analyses of biochemical tracers in several tissues (fin clip, muscle, liver, red blood cells; RBC) and plasma, our results revealed significant interspecific differences in tracers between the two species. Total FAs (∑saturated FA, ∑monounsaturated FA and ∑polyunsaturated FA) and trophic biomarkers (i.e., docosahexaenoic acid, arachidonic acid, oleic acid and δ15 N) were the principle tracers responsible for the differences detected. These data revealed that R. brasiliensis was less enriched in physiologically important essential FAs than R. bonasus. Our findings suggest that these congeneric species differ in maternal investment strategy and moderately partition food resources over relatively fine spatial scales within a single nursery habitat to limit competition. These results provide further knowledge on the foraging strategies adopted by batoids in communal nursery areas, information that is required for improving spatial conservation and management planning.