The distribution and abundance of aerial seabirds in relation to Antarctic krill in the Prydz Bay region, Antarctica, during late summer

Summary

The distribution patterns of aerial seabirds are analysed from counts made in the Prydz Bay region, Antarctica, during the African legs of SIBEX I and II in late summer (end of February to April), and compared with those made farther west at the same time of year during FIBEX. Species composition and abundances were similar in all three surveys, with sooty shearwaters Puffinus griseus contributing approximately half of the total aerial bird energy demand. Differences between surveys are explained in terms of longitudinal or seasonal differences in sampling areas and periods. Correlations between bird distribution patterns and environmental parameters are used to infer the scale-dependent factors affecting bird dispersion at sea. Two macro-scale bird assemblages, identified by physical parameters, were separated along latitudinal gradients (temperature and salinity) associated with the Antarctic Divergence. These assemblages are consistent with the Intermediate and Southern High Latitude Groups identified during FIBEX. At smaller spatial scales, almost all species were correlated with the abundance of Antarctic krill Euphausia superba, both across the entire SIBEX I grid, and within the areas north and south of the Antarctic Divergence. Similarly, during SIBEX II, seabird densities were six times greater when krill was abundant than when krill was scarce. Sooty shearwaters, which appeared to be moving through the area, were the only abundant bird species not correlated with krill abundance. Possible reasons why previous studies have not detected correlations between seabird and krill abundances are discussed.