Spatial association between hotspots of baleen whales and demographic patterns of Antarctic krill Euphausia superba suggests size-dependent predation

Abstract

We examined the spatial association between baleen whales and their principal prey, Antarctic krill Euphausia superba near the South Shetland Islands (Antarctic Peninsula) using data collected by the US Antarctic Marine Living Resources (AMLR) program during January surveys from 2003 through 2007. Whale distributions were determined using ship-based visual surveys, while data on krill distribution, abundance, and demographic characteristics were derived from net hauls. Approximately 25 000 km of transects and 500 net hauls were sampled over 5 yr. We defined hotspots based on statistical criteria to describe persistent areas of occurrence of both whales and krill. Hotspots were identified, and whales and krill length-maturity classes exhibited distinct spatial segregation in their distribution patterns. We found that baleen whales aggregated to krill hotspots that differed in size structure. Humpback whales Megaptera novaeangliae were associated with small (<35 mm) juvenile krill in Bransfield Strait, whereas fin whales Balaenoptera physalus were associated with large (>45 mm) mature krill located offshore. Overlapping these size-dependent krill distributions, Antarctic minke whales B. bonaerensis were associated with intermediate sized krill (35-44 mm). The correlation among different whale species and krill swarms of differing size composition presents an intriguing pattern that deserves further study. © Inter-Research 2010.