Rhinoceros auklet reproduction, survival and diet in relation to ocean climate.

摘要

Ocean climate affects the demography of top marine predators, likely through changes in local prey availability. In the California Current ecosystem, abundance and distribution of mid trophic-level forage fish may be affected by variability in upwelling. Upwelling systems, however, may be particularly vulnerable to climate change since temperature increases may intensify upwelling, altering enrichment, concentration and retention processes and affecting biological production. Changes in the California Current are already evident. Reductions in rockfish (Sebastes spp.) abundance in the past decade have changed the food web in which rockfish were historically prominent. Anchovy (Engraulis mordax) has become a more important alternate prey. Conventional life-history theory suggests that reproduction rather than survival of long-lived species should be affected by environmental conditions. I examined the reproductive ecology and survival of rhinoceros auklets Cerorhinca monocerata relative to ocean climate and the availability of forage species between 1993-2006 for two central California colonies. The first estimates worldwide of juvenile return rates, immigration and age at first breeding for rhinoceros auklets are reported. Effects from upwelling (as indexed by local SST) and forage fish availability were seen on both reproduction and survival and were similar between colonies, but the degree of variation differed despite close colony proximity. The offshore S.E. Farallon Island population exhibited higher mean adult survival, but lower productivity, while the opposite was observed at inshore Ano Nuevo Island, suggesting trade-offs with a different equilibrium for each population. Environmental thresholds below which both reproduction and survival suffered occurred during extreme climate conditions. These responses were more apparent offshore than inshore and may be related to local upwelling cells and prey distribution. I also demonstrated that auklet diet can reflect primary prey dynamics. Diet was then used as an indicator of forage fishes to test for synchrony and influence of ocean climate around the North Pacific Rim. Significant SST-fish relationships and inter-annual synchrony of fishes was observed for several regions in the eastern Pacific, but there were no significant east-west correlations. Predator diet sampling offers a fishery-independent, large-scale perspective on forage fish dynamics that may be difficult to obtain using conventional means of study.