Climate variability and multi-scale assessment of the krill preyscape near the north Antarctic Peninsula

Antarctic krill (Euphausia superba) densities vary in space and time across multiple scales, with consequences for krill predators, the krill fishery, and management decisions. We use acoustic data collected from 1997 to 2011 around the South Shetland Islands near the northern Antarctic Peninsula to quantify spatiotemporal patterns in krill biomass, distribution, and patchiness both within and across years. Moreover, we evaluate potential climate drivers of krill biomass and spatial organization through comparison with seasonally lagged climate indices. Krill abundance varied by an order of magnitude throughout the study period, with mean biomass ranging from a high of 171.9 g m−2 in 1997 to a low of 9.4 g m−2 in 2002. We find that across years, krill abundance and variability are correlated with seasonally averaged measures of El Niño-Southern Oscillation at lags of approximately 2–2.5 years, which may correspond to strong reproduction and recruitment events. Krill biomass shows generally weak to moderate spatial autocorrelation and high aggregation, with measures of spatial organization correlated with abundance in some habitats. Within years, there was an overall trend of declining krill abundance and/or detectability and contracted spatial distribution between midsummer and late summer, but this pattern was not consistent across all years. This synthesis provides the background to model krill prey landscapes in order to better understand regional foraging ecology of krill predators and fishery performance.