Changes in oceanographic conditions off northern British Columbia (1983-1999) and the reproduction of a marine bird, the Ancient Murrelet (Synthliboramphus antiquus)

We examined variation in breeding-biology parameters for Ancient Murrelets (Synthliboramphus antiquus), marine birds breeding in central Hecate Strait , British Columbia, over the period 1983-1999. Interannual changes were com pared with physical oceanographic data (sea-surface temperatures (SSTs) and Southern Oscillation (SO) indices) for surrounding waters. No secular chan ge in oceanographic data for Hecate Strait was detectable for the period co nsidered, which embraced two major (1982-1983, 1997-1998) and three minor E l Nino - Southern Oscillation (ENSO) events. SSTs were strongly related to the SO index for the area considered. Breeding-biology data were not availa ble for the 1982-1983 ENSO. The 1997-1998 ENSO had a strong effect on breed ing success, reducing the number of chicks per pair from >1.4 to below 1; m ost of this effect was caused by desertions before incubation began. We fou nd a positive correlation between May SST and the slope of the regression o f chick mass at colony departure on a particular date for a given year. Thi s effect may have resulted from the failure of young or otherwise less comp etent birds to rear young in years of high SSTs. Both the median date of co lony departure and chick mass at departure declined over the period of the study, although neither effect was related to changes in the oceanographic variables considered in this study. These trends may relate to longer term changes in oceanographic conditions in the North Pacific Ocean. If they con tinue, the recent trend towards lower chick masses at colony departure may have adverse effects on recruitment and eventually on Ancient Murrelet popu lations.