The minke whale (initially Baleanoptera acutorostrata) was named by Lacépède in 1804, and a subspecies difference between the Northern and Southern Hemispheres was proposed by Burmeister in 1867. The formal elevation of the Antarctic minke whale (B. bonaerensis) to full species status was proposed by Rice in 1998 (though this classification had been used occasionally before that time), and was based largely on recent genetic data, much of which was described in the IWC Special Issue volume 13. These studies, based on various genetic markers, indicated a difference as substantial as for other pairs of species in the same genus.
Size, shape and distinctive characteristics
Minke whales are the smallest of the so-called 'finner' whales (species in the genus Balaenoptera). Other whales in this group include the Bryde's (B. edeni), sei (B. borealis), fin (B. physalus), and blue whale (B. musculus). All are highly streamlined, fast swimmers, with a falcate dorsal fin towards the posterior end of the body (hence the term 'finners'). They are further characterised by numerous throat grooves extending from the rostrum to posterior of the pectoral flippers, which permit the very broad extention of their bucal cavity during feeding. This exposes the pink skin within the grooves, and has given them another nickname, the 'rorquals' (from the Norwegian for 'red whale'). Their baleen is proportionally shorter than that of the right whales (Balaenidae), but fine enough to permit the sieving of small fish and krill. The southern (or 'Antarctic') minke whale is distinct from the northern (or 'common') minke whale in its size at sexual maturity (up to 35 ft compared to 30 ft for the northern species), and in the coloration of its pectoral fins. These are grey in the southern species, lacking the bright white band found in the northern species. The male is somewhat shorter than the female (up to 32 ft in the southern minke whale), and the average weight of an adult is about 9 tons. All minkes have a chevron, typically in three parts, that varies in brightness and extends along the flanks from just behind the pectorals to below the dorsal fin. It tends to be less pronounced in the southern species. The southern species has about 460-720 baleen plates, the longest of which is 30cm in length, and 50-70 throat grooves.
The southern minke whale has a circumpolar distribution in the southern oceans, with some general redistribution over the course of the seasons, as is typical for baleen whales (but less pronounced in this species than for some, and poorly understood). In the austral summer they are typically found in the Antarctic zone, often close to the pack ice. In the winter they are more often further north (often between 7 and 35 degrees south).
Ecology and Behaviour
Minke whales tend to be solitary, but can also be seen in groups (especially in the Antarctic and when feeding), sometimes showing coordinated movement, though this doesn't typically last very long. When diving they lift their peduncle, but their flukes only rarely break the water surface. They are capable of swimming at speeds in excess of 20mph, and sometimes porpoise and breach. The southern species is more likely to show a visible blow than the northern species, and when seen it is narrow and 5-10 ft tall. Their vocal behaviour is typically comprised of short low frequency moans and 'thump trains'.
The southern minke is thought to live to about 60 years. Sexual maturity is at 7-8 years, and females are on average 26 ft at maturity. Mating is thought to be primarily between June and December, with a peak in calving during May and June. Gestation lasts for 10 months. Typically there is just one calf though twins (0.56%) and triplets (0.03%) do occur. The calves grow at approximately 1cm per day and are weaned at about four to five months. Natural mortality includes predation by killer whales.
The southern minke whale eats mostly euphausiids (krill), but may also take bate fish or copepods when in lower latitudes. They often lunge at the surface when feeding. Prey species are nearly exclusively Euphausia superba near the Antarctic ice edge, and a mixture of krill species further offshore. Feeding at the ice edge is more common early in the day.
In the 1980s there were approximately 500,000 to 1.1 million southern minke whales in the Antarctic. More current estimates are in the process of being derived through the IWC.
B. bonaerensis is listed as 'Lower Risk: Conservation Dependent' by the IUCN, and is also listed on Appendix I of CITES.
This species was considered commercially uneconomical for the whaling industry until stocks of larger whales became depleted. It became the main target for whaling operations in the 1970s until 1986 when the IWC's moratorium on commercial whaling came into effect. Since that time there have been continuing takes by the Japanese under IWC scientific permit, and minke whale meat has continued to enter the market through this process. These takes have been quite substantial, for example 3,751 minke whales were taken under permit in the southern oceans during the 1990's. Stock definition within the Antarctic remains poorly understood, largely because there is little known about breeding grounds and the movement of whales between breeding grounds and feeding grounds in the Antarctic.
Best PB (1982) Seasonal abundance, feeding, reproduction, age and growth in minke whales off Durban (with incidental observations from the Antarctic). Reports of the International Whaling Commission. 32:759-786.
Hoelzel AR (Ed) (1991) Genetic Ecology of Whales and Dolphins. IWC Special Issue 13.