Prey composition and nutritional strategies in two sympatric pinnipeds

Abstract

Niche segregation has been recognized as a valuable mechanism for sympatric species to reduce interspecific competition and facilitate coexistence. The differential use of habitats is one of the behavioural mechanisms that may shape coexistence among marine predators. In this study, we provide a dietary and nutritional assessment of two pinnipeds, the South American sea lion (SASL) and the South American fur seal (SAFS) and explore their sympatric coexistence within the Warm Temperate Southwestern Atlantic biogeographic province (WTSA province). Pelagic prey species within the WTSA province showed significantly higher proportional composition of lipids than demersal counterparts, evidencing a nutritional variability in a vertical dimension accessible to marine predators. By modelling the dietary niches of these pinnipeds through a nutritional lens, we showed high overlapping prey composition niche breadths suggesting that both species consumed prey with similar nutritional composition; however, distinct realized nutritional niches showed that diets are likely shaped by differences in foraging behaviours. The SAFS combined pelagic and demersal prey, whereas SASL mostly preyed upon demersal species. This paper provides crucial information on how nutritional variability in the water column likely drives the feeding strategies of both pinnipeds in the WTSA province. Given that this variation can influence the stability of the contrasting population trends shown by these two pinnipeds, nutritional dynamics must be taken into consideration when defining conservation strategies.