Interannual variations in the diet of breeding sooty shearwaters (Puffinus griseus)

Diet samples from sooty shearwaters (Puffinus griseus) were collected during the breeding season at Poutama (Evening) Island (1994 & 1995) and Putauhinu (Hidden) Island (1996-1998), southern New Zealand. Regurgitate samples and whole guts were obtained from chicks harvested by Rakiura Maori muttonbirders. The relative proportions of six major prey categories (decapod, fish, squid, euphausiid, salp and amphipod) varied markedly between years and/or islands. Many more decapods were eaten in 1994 than 1995 (regurgitates). More euphausiids, amphipods and squid were eaten in 1997 than in 1998 (stomachs). The number of regurgitates with identifiable prey remains was significantly higher in 1998 than 1997. Many of the differences in diet between Poutama and Putauhinu probably reflected interannual diet variation rather than site-specific differences, because the two nearby islands were sampled in different years. Interannual variation in diet may correlate with fluctuations in adult survival and breeding success that strongly influence sooty shearwater population dynamics.