The Antarctic minke whale or southern minke whale (Balaenoptera bonaerensis) is a species of minke whale within the suborder of baleen whales. It is the second smallest rorqual after the common minke whale and the third smallest baleen whale. Although first scientifically described in the mid-19th century, it was not recognized as a distinct species until the 1990s. Once ignored by the whaling industry due to its small size and low oil yield, the Antarctic minke was able to avoid the fate of other baleen whales and maintained a large population into the 21st century, numbering in the hundreds of thousands. Surviving to become the most abundant baleen whale in the world, it is now one of the mainstays of the industry alongside its cosmopolitan counterpart the common minke. It is primarily restricted to the Southern Hemisphere (although vagrants have been reported in the North Atlantic) and feeds mainly on euphausiids.
Taxonomy
History
In February 1867, a fisherman found an estimated male rorqual floating in the Río de la Plata near Belgrano, about ten miles from Buenos Aires, Argentina. After bringing it ashore he brought it to the attention of the German Argentine zoologist Hermann Burmeister, who described it as a new species, Balaenoptera bonaerensis, the same year. The skeleton of another specimen, a individual taken off Otago Head, South Island, New Zealand, in October 1873, was sent by Professor Frederick Hutton, keeper of the Otago Museum in Dunedin, to the British Museum in London, where it was examined by the British zoologist John Edward Gray, who described it as a new species of "pike whale" (minke whale, B. acutorostrata) and named it B. huttoni. Both descriptions were largely ignored for a century.
Gordon R. Williamson was the first to describe a dark-flippered form in the Southern Hemisphere, based on three specimens, a pregnant female taken in 1955 and two males taken in 1957, all brought aboard the British factory ship Balaena. All three had uniformly pale gray flippers and bicolored baleen, with white plates in the front and gray plates in the back. Further studies in the 1960s supported his description. In the 1970s osteological and morphological studies suggested it was at least a subspecies of the common minke whale, which was designated B. a. bonaerensis, after Burmeister's specimen. In the 1980s further studies based on external appearance and osteology suggested there were in fact two forms in the Southern Hemisphere, a larger form with dark flippers and a "diminutive" or "dwarf form" with white flippers, the latter of which appeared to be more closely related to the common form of the Northern Hemisphere. This was strengthened by genetic studies using allozyme and mitochondrial DNA analyses, which proposed there were at least two species of minke whale, B. acutorostrata and B. bonaerensis, with the dwarf form being more closely related to the former species. One study, in fact, suggested that sei whales and the offshore form of Bryde's whale were more closely related to one another than either species of minke whale were to each other. The American scientist Dale W. Rice supported these conclusions in his seminal work on marine mammal taxonomy, giving what he called the "Antarctic minke whale" (B. bonaerensis, Burmeister, 1867), full specific status – this was followed by the International Whaling Commission a few years later. Other organizations followed suit.
Divergence
Antarctic and common minke whales diverged from each other in the Southern Hemisphere 4.7 million years ago, during a prolonged period of global warming in the early Pliocene which disrupted the Antarctic Circumpolar Current and created local pockets of upwelling, facilitating speciation by fragmenting populations.
Hybrids
There have been two confirmed hybrids between Antarctic and common minke whales. Both were caught in the northeastern North Atlantic by Norwegian whaling vessels. The first, an female taken off western Spitsbergen () on 20 June 2007, was the result of a pairing between a female Antarctic minke and a male common minke. The second, a pregnant female taken off northwestern Spitsbergen () on 1 July 2010, on the other hand, had a common minke mother and an Antarctic minke father. Her female fetus, in turn, was fathered by a North Atlantic common minke, demonstrating that back-crossing is possible between hybrids of the two species.