Temporal variation in the diet of Yangtze finless porpoise calls for conservation of semi‐migratory fish

Abstract

Abstract Identifying the feeding patterns of large‐bodied predators is necessary to predict their potential effects on food‐web dynamics and to inform species conservation. In contrast to diet information from stomach contents, diet estimates obtained using stable isotopes in blood and muscle can reveal temporal variation in diets. Here, we used an extensive stable isotope dataset and Bayesian stable isotope mixing model to evaluate the trophic role of the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), a critically endangered species distributed in the middle and lower catchments of the Yangtze River. We analysed blood samples from 24 individuals captured during March 2017 in Poyang Lake (which adjoins the Yangtze River), and muscle samples from 8 individuals stranded in the lake over a 1‐year period (2012–2013). We additionally genotyped prey from faecal samples taken from 13 individuals captured in March 2017. We found that as a generalist apex predator, this finless porpoise consumes semi‐migratory and non‐migratory fish prey. However, relative proportions of these two prey resources were different between dietary analyses based on blood samples compared to muscle samples, reflecting recent and longer‐term consumption patterns, respectively. Non‐migratory fish contributed mainly to the diet of predators in the early and middle of March. In contrast, semi‐migratory fish comprised the majority of the prey composition over a more extended period (e.g. 2–3 months), and the difference may be linked to changes in the fish abundance influenced by seasonal factors. Our findings provide insights into the trophic role of this critically imperilled but little studied species, demonstrate how stable isotope analyses can elucidate finless porpoise feeding ecology, and emphasise the importance of semi‐migratory fish to conserving this porpoise population.