The importance of Antarctic krill in the non-breeding and breeding diet of gentoo penguins at a colony of the South Shetland Islands

Abstract

Understanding predator–prey relationships is essential to monitor Antarctic marine ecosystem structure and function, assess changes in prey and predator abundances, and provide tools for efective conservation measures. Despite this, diet studies of Antarctic predators conducted with traditional methods are limited outside the breeding period mainly due to constraints associated with the life-history strategies of the predators and the sampling logistics and operability. At Stranger Point/Cabo Funes (25 de Mayo/King George Island), the diet composition of gentoo penguins (Pygoscelis papua) was characterized during four stages of the annual cycle (i.e. non-breeding and pre-breeding stages of 2022, and guard and crèche stages of the 2022/2023 breeding season) by the analysis of stomach contents obtained by using the water-ofoading technique. Antarctic krill (Euphausia superba) dominated the diet of gentoo penguins in terms of frequency of occurrence and percentage in mass, followed by fsh and amphipods. However, the diet composition changed seasonally, with a decrease in the contribution of fsh and amphipods as the year progressed. Furthermore, higher individual variability was observed outside the breeding period than during the chick-rearing period. Our results indicate that krill was an important fraction of the non-breeding and breeding diet. However, outside the breeding period, the mean krill size consumed was smaller and the proportion of juvenile krill was higher than that recorded in the chick-rearing period. Thus, sampling the diet of the gentoo penguin outside the breeding period could provide valuable information on the krill size composition during the austral autumn and winter.