Evidence of eastern rockhopper penguin feeding on a key commercial pelagic arrow squid species

Abstract

Abstract Cephalopods play an important role in the Southern Ocean marine ecosystem connecting top predators and mid-trophic organisms. However, there is a lack of knowledge of the ecology of cephalopod fauna in the Pacific sector of the Southern Ocean. Stable isotope analysis (SIA) was applied to study the habitat and trophic ecology of cephalopods in the diet of eastern rockhopper penguin (Eudyptes chrysocome filholi) around Campbell Island, a New Zealand sub-Antarctic island. We assessed differences in the cephalopod component between two penguin breeding seasons, 1986-87 and 2012-13. Season 1986-87 showed a more diverse diet (7 vs. 3 species) without differences in size between the common species, Moroteuthopsis ingens and Octopus campbelli. In 2012-13, M. ingens was replaced by the squid Nototodarus sloanii in the penguin diet, suggesting changes in cephalopod biodiversity. Furthermore, δ13C and δ15N values of M. ingens revealed no significant differences between years, indicating stability in habitat and feeding ecology. However, O. campbelli displayed changes in δ13C and δ15N values, suggesting shifts in habitat and feeding habits. Environmental data indicated warmer oceanic temperatures around Campbell Island in 2012-13, possibly supporting the presence of N. sloanii. Our findings suggest changes in cephalopod biodiversity and the penguin diet between the two breeding seasons may have occurred. The presence of N. sloanii, a commercially valuable species, in later years highlights the significance of further research to explore the ecological dynamics between cephalopods and the local marine environment in this region.