Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula

Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km2) of humpback whales (Megaptera novaeangliae...

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Bibliographic Details
Published in:PLoS ONE
Main Authors: Nowacek, Douglas P., Friedlaender, Ari S., Halpin, Patrick N., Hazen, Elliott L., Johnston, David W., Read, Andrew J., Espinasse, Boris, Zhou, Meng, Zhu, Yiwu
Format: Text
Language:English
Published: Public Library of Science 2011
Subjects:
Research Article
Antarctic
Antarctic Peninsula
Austral
Southern Ocean
Wilhelmina
Wilhelmina Bay
Antarc*
Antarctic Krill
baleen whale
baleen whales
Euphausia superba
Megaptera novaeangliae
Sea ice
Online Access:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3083408
http://www.ncbi.nlm.nih.gov/pubmed/21556153
https://doi.org/10.1371/journal.pone.0019173
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Summary:Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km2) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km2 at densities of up to 2000 individuals m−3; reports of such ‘super-aggregations’ of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.

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