Distribution and diet of cape petrels (Daption capense) attending fishing vessels off the Patagonian Continental Shelf during the non-breeding season in austral winter: insights from on-board censuses and stable isotope analysis

Abstract

The cape petrel (Daption capense) is an abundant procellariform in seabird assemblages attending fishing vessels in the Southwestern Atlantic Ocean. The bulk of extant information comes from surveys conducted during the breeding season at Antarctic and sub-Antarctic sites; however, most of their ecological aspects during the non-breeding season remain largely unknown. We performed on-board census and stable isotope analysis in blood and feathers from 30 adult petrels during the non-breeding season in waters off Argentina. Cape petrels attending ice trawlers showed a higher abundance during winter compared to other seasons. The lack of correlation of isotopic values between tissues suggests changes in the diet and foraging locations between the moulting period and the non-breeding season. Isotopic mixing models revealed low-trophic-level sources as the main contributors to this petrel’s diet while pelagic-demersal fish species targeted by fishing vessels showed the lower contribution. The discrepancies between methods could be a result of partial use of offal/discards or low use of these due to size/mechanic limitations. These findings reinforce the idea of zooplankton and small-pelagic fish facilitation during the hauling operatory and the relevance of combining different methods for a thorough understanding of prey-predator relationships.