Dietary evidence of trophic segregation between Campbell albatross Thalassarche impavida and grey-headed albatross T. chrysostoma at subantarctic Campbell Island

Diet and trophic relationships of New Zealand albatrosses are poorly known, while comprehensive information on their feeding ecology are needed in an ecological and evolutionary context, but also for effective conservation management. Here, food samples of the sympatric Campbell albatross Thalassarche impavida and grey-headed albatross T. chrysostoma were collected at subantarctic Motu Ihupuku Campbell Island to (1) detail their prey items, (2) investigate segregating mechanisms allowing co-existence, and (3) look at potential overlaps between albatrosses and human activities. Chick food of the two albatrosses overlapped greatly in terms of the most consumed prey species but segregated in terms of prey groups. The most abundant item was epipelagic young-of-the-year Micromesistius australis, a species that is commercially-exploited when adult. The myctophid Electrona carlsbergi and various macrourids constituted other significant fish prey, while juveniles of Moroteuthopsis ingens and Martialia hyadesi were the main squid prey. Campbell albatross fed their chicks more on fish (79% vs. 27% by mass) and grey-headed albatross more on cephalopods (67% vs. 18%). Albatrosses also segregated by their foraging habitats, with Campbell albatross favoring neritic prey and grey-headed albatross oceanic prey from colder waters. A few plastic debris and no fishery-related items were found in food samples, indicating limited interactions with human activities at the time of sample collection. However, the nutritional importance of naturally-caught juvenile M. australis for albatrosses has to be taken into account for a sustainable management of the resource, its predators and the trawl fishery targeting adult fish.