Relationships between the distributions of marine avian predators and their prey, Euphausia superba, in Bransfield Strait and southern Drake Passage, Antarctica

Abstract

We investigated the joint distributions of seabirds and krill (primarily Euphausia superba ) in Bransfield Strait on southern Drake Passage, Southern Ocean. We estimated seabird and krill densities, simultaneously and continuously using visual and acoustic techniques while traversing a transect grid standardized for the Second International BIOMASS Experiment (SIBEX) program. This is one of only 3 studies to find a correlation between the densities of seabirds and their prey. We defined 2 statistically independent components of distributional correlation: "spatial concordance", the tendency for predators and prey to co-occur in the same sampling unit, and "numerical concordance", the tendency for densities of spatially concordant predators and prey to covary. Within nautical-mile transect intervals, we found cape petrels Daption capensis and antarctic fulmars Fulmarus glacialoides spatially concordant, and cape petrels, and adelie penguins Pygoscelis adeliae numerically concordant with krill.; Within nautical-mile transect intervals, we found cape petrels Daption capensis and antarctic fulmars Fulmarus glacialoides spatially concordant, and cape petrels, and adelie penguins Pygoscelis adeliae numerically concordant with krill. A few large concentrations of seabirds and krill accounted for the majority of seabird and krill biomass. In general, species specializing on krill as a food resource showed the highest degree of distributional correlation with krill, and species using less than 50% krill in their diets showed little evidence of distributional correlation with krill.