Krill biomass and aggregation structure in relation to tidal cycle in a penguin foraging region off the Western Antarctic Peninsula

This is a pre-copy-editing, author-produced PDF of an article accepted for publication in ICES Journal of Marine Science following peer review. The definitive publisher-authenticated version, Bernard, K.S., & Steinberg, D.K. (2013). Krill biomass and aggregation structure in relation to tidal cycle in a penguin foraging region off the Western Antarctic Peninsula. ICES Journal of Marine Science, 70(4), 834-849. doi:10.1093/icesjms/fst088, is available online at: http://icesjms.oxfordjournals.org/content/70/4/834.\ud The published article is copyrighted by the International Council for the Exploration of the Sea (ICES) and published by Oxford University Press.Antarctic krill are a key component of the diet of Adélie penguins inhabiting the Western\ud Antarctic Peninsula (WAP), yet our understanding of the variability of krill distribution\ud patterns within nearshore penguin feeding grounds is limited. A recent study of the foraging\ud patterns of penguins breeding in the northern WAP suggests that tidal phase plays a role in\ud foraging distance. We used acoustics to examine biomass and aggregation structure of krill in\ud the penguin foraging grounds off Palmer Station during diurnal and semi-diurnal tides.\ud Nearshore, integrated krill biomass during diurnal tides was significantly higher than during\ud semi-diurnal tides. Krill aggregations were also shallower, closer together, and larger in\ud dimension during diurnal tides. Conversely, krill aggregations had higher volumetric biomass\ud and abundance during semi-diurnal tides. Further offshore, at the head of the Palmer Deep\ud canyon, krill aggregations were similar to those observed nearshore during diurnal tides (i.e.,\ud shallow, close together, and large in dimension). Since krill aggregation structure strongly\ud influences availability as a potential prey source, we suggest that foraging behavior of Adélie\ud penguins in this region is strongly linked to the variability in nearshore krill aggregation\ud structure as well as biomass