We investigated seabird-eddy associations in subtropical waters of the southern Indian Ocean during a summer (January) cruise from Amsterdam Island to Western Australia. To determine habitat associations and to enable predictions about foraging strategies, we related the distributions of satellite altimetry data (sea surface height anomalies) to the 3 most abundant taxa in the study area: terns (sooty Sterna fuscata and bridled S. anaethetus) and shearwaters (wedge-tailed Puffinus pacificus) were significantly more common and numerous within convergence zones. However, a step-wise logistic regression model revealed that these seabirds were more strongly associated with other habitat variables, including the distance to breeding colonies and warm sea surface temperature conditions. Great-winged petrels Pterodroma macroptera were widely scattered and did not show associations with convergences or divergences. These contrasting results highlight the need to consider smaller-scale hydrographic features, such as frontal systems, when guantifying seabird associations with mesoscale eddies. Large-scale patterns of ocean circulation and mesoscale variability also seem to play a critical role in determining the extent of seabird-eddy associations. In contrast with previous studies, which have focused on dynamic frontal regions and energetic current systems, we surveyed a region of weak mesoscale variability north of the Subtropical Convergence zone. © Inter-Research 2006.

During summer 1997, hundreds of thousands of emaciated short-tailed shearwaters (Puffinus tenuirostris) died in the south-eastern Bering Sea. Using strip transect methodology, we documented the distribution and abundance of short-tailed shearwaters during cruises conducted prior to, during, and after the die-off, as well as the distributions and abundances of floating carcasses. The distributions and abundances of short-tailed shearwaters in 1997 were similar to those found during the 1970s and early 1980s. In August-September 1997, we observed 163 floating shearwater carcasses, most of which were between St Paul Island and Nunivak Island. We estimated ∼ 190 000 carcasses were afloat in the study area, about 11% of the surveyed population. Between spring (June) and autumn (August/September), mean net body mass of shearwaters decreased by 19%, mean pectoral muscle mass decreased by 14%, and mean percentage body lipid content decreased by 46%, from 15.6% in spring to 8.4% in autumn. Compared with spring, short-tailed shearwater diets broadened in autumn 1997, to include, in addition to adult euphausiids Thysanoessa raschii, juveniles of T. inermis, T. raschii and T. spinifera, crab megalops, fish and squid. We discuss how the ecosystem anomalies in the south-eastern Bering Sea during spring and summer 1997 relate to the mortality event and suggest possible implications of long-term climate change for populations of apex predators in the south-eastern Bering Sea.

This report summarizes physical and biological conditions in the California Current System (CCS), from Oregon to Baja California, in 2001 and 2002. The principal sources of the observations described here are the CalCOFI (California Cooperative Oceanic Fisheries Investigations), IMECOCAL (Investigaciones Mexicanas de la Corriente de California), and U.S. GLOBECLTOP (Global Ecosystems Long-term Observation Program) programs. Large-scale atmospheric and oceanic conditions in the Pacific point to a fourth consecutive La Niña-like year. This has contributed to generally stronger than normal upwelling and uncharacteristically cool waters in much of the CCS, a pattern that has persisted since late 1998. Biological productivity has been generally higher as well, particularly off Oregon. Within the observed interannual fluctuations of recent years, these conditions suggest a generally elevated production off California and Oregon, but cool conditions have led to lower than normal zooplankton biomass off Baja California. Although the tropical Pacific has exhibited some indications of a developing El Niño, it is not likely to impact the CCS during the productive upwelling season of 2002. These observations are continuing evidence that a regime shift may have occurred in 1998, resulting in substantial change in ecosystem structure in the CCS. Continued monitoring and analysis of the state of the CCS in this context is needed. We outline a plan for an integrated monitoring program for the entire region, through the creation of ACCEO (Alliance for California Current Ecosystem Observation).