Killer whales (Orcinus orca), both ecotype-B and-C, are important to the Ross Sea, Antarctica, ecosystem; the type-C referred to hereafter as “Ross Sea killer whale ” (RS killer whale). Herein we review existing data on occurrence patterns and diet of RS killer whales, and present data on numbers ob...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.552.6348 http://www.iwcoffice.co.uk/_documents/sci_com/SC61docs/SC-61-SM26.pdf |
| Summary: | Killer whales (Orcinus orca), both ecotype-B and-C, are important to the Ross Sea, Antarctica, ecosystem; the type-C referred to hereafter as “Ross Sea killer whale ” (RS killer whale). Herein we review existing data on occurrence patterns and diet of RS killer whales, and present data on numbers observed in the southwestern Ross Sea. These “resident ” whales appear to feed principally on fish, including Antarctic toothfish (Dissostichus mawsoni). On the basis of sea watches on the outer coast of Ross Island beginning in 2002-03, sighting frequency and average group size began to decrease beginning 2006-07 and thereafter; prevalence also decreased in nearby McMurdo Sound. We discuss trends with respect to environmental change as well as the initiation of industrial fishing for toothfish beginning in 1996-97. Consistent with a decrease in the catch-per-unit-effort of scientific fishing for toothfish in McMurdo Sound, we suggest that the change in Ross Sea killer whale numbers is related to a contraction of the toothfish stock, and not to changes in the physical environment. We surmise that in this closely-coupled foodweb, composed of very abundant penguin, seal and whale components, loss of the toothfish option for Ross Sea killer whales would force more direct competition for the smaller-fish prey. Therefore, the killer whales have opted to move out of the region. |
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