We review the scientific information on whales that could be indicative of historical and current changes in the ecosystem in the Indo-Pacific sector of the Antarctic. The increased krill availability in the middle of the past century as a result of the heavy harvesting of the larger baleen whale species could have been translated into better nutritional conditions for the Antarctic minke whale, resulting in a decreasing trend in the age at sexual maturity and an increasing trend in recruitment rate and hence total population size between approximately 1940 and 1970. This nutritional condition has deteriorated more recently, as revealed by a decrease in energy storage and stomach content weight since the 1980’s; these changes coincide with appreciable increases in the abundances of humpback and fin whales, which were heavily harvested in the first half of the past century. The historical demographic changes observed in the Antarctic minke whale are consistent with the pattern to be expected under the krill surplus hypothesis, with minke whales now again competing with other (recovering) baleen whale species for krill. However, these minke whales could also be using alternative feeding areas (e.g. polynias within the pack-ice) in response to the increase in abundance and geographical expansion of these other large whale species. This could provide an alternative explanation for indications from sighting surveys and population models of a decrease and then re-stabilisation of minke whale abundance in open water areas since the 1970s.
Part of the book: Glaciers and the Polar Environment
In 1998, two species of minke whales were recognized based on the review of the morphological and genetic information available at that time: the Antarctic minke whale (Balaenoptera bonaerensis), which is restricted to the Southern Hemisphere, and the cosmopolitan common minke whale (Balaenoptera acutorostrata). Furthermore, three sub-species of the common minke whale were recognized: the North Atlantic (B. a. acutorostrata), North Pacific (B. a. scammoni) and Southern Hemisphere (B. a. subsp.). This chapter reviews the genetic studies on minke whales conducted after 1998. The review is organized by topic, e.g., those studies focused on phylogeny and other matters most relevant for taxonomy, and those focused on population genetic structure within oceanic basins most relevant for conservation and management. On the former topic, the new genetic information, whilst strongly supporting the minke whale taxonomic classification recognized in 1998, also reveals substantial genetic differentiation within the Southern Hemisphere common minke whales, with subsequent taxonomic implications. On the latter topic, results from different analytical procedures have provided information on population identification and structure in the Indo-Pacific sector of the Antarctic and western North Pacific, but they have failed to identify unequivocally any population within the North Atlantic common minke whales.
Part of the book: Marine Mammals