Establishment of a stable isotope database for New Zealand fur seal breeding colonies using δ13C and δ15N in pup vibrissae

Abstract

The New Zealand fur seal/kekeno (Arctocephalus forsteri, NZFS) is native to Aotearoa/New Zealand. Its original range included the entire coast of mainland New Zealand, and offshore and subantarctic islands. The NZFS has gradually recolonised much of its former range after being almost extirpated by hunting, however, little is known about species dispersal in the non-breeding season. Stable isotope analysis (SIA) can trace foraging ecology and migration in marine mammal species. Isotopic niche width can be described statistically and provides ecologically relevant information on diet and potentially foraging location. Otariid pup vibrissae (whiskers) can be used as proxies for maternal foraging as they provide a sequential record of nutrient intake derived from maternal milk. In this study, vibrissae from NZFS pups were collected from seven established breeding areas around the coast of New Zealand. A stable isotope database of δ13C and δ15N was established for each breeding colony, and isotopic niche widths estimated. Isotopic niche widths were largest at Open Bay Islands and Cape Foulwind. Results were discussed in light of previous oceanographic and NZFS diet and foraging studies. Colonies are not likely to be sufficiently isotopically distinct for pups to be identified to their colony of origin.