Changes in sooty shearwater Puffinus griseus chick production and harvest precede ENSO events

Abstract

A large-scale decline in the population of an apex marine predator, the sooty shearwater Puffinus griseus, in the North Pacific was corroborated by decreased harvest rates of a muttonbirder between 1979 and 1998 in New Zealand. Between 1989 and 1998 harvest rates decreased by 47% in the nanao (burrow prospecting) period and 42% in the rama (nightly capture of emerging chicks) period. The number of muttonbirders harvesting on Poutama Island decreased over the 20 yr as chicks became scarcer, suggesting that the harvest is potentially self-regulating. Chick abundance on an unharvested island also declined over the last decade, suggesting that harvest was not a sufficient sole cause for the decline. Changes in harvest rates and burrow occupancies between successive years significantly predicted the direction and intensity of Southern Oscillation and sea-surface temperature anomalies in the following 12 mo. Climatic perturbations may affect food availability, predominant wind characteristics, direct and indirect fishery pressure and PCB/DDE redistribution in sooty shearwaters.