Minke Whales: Balaenoptera acutorostrata and B. bonaerensis

Until relatively recently, only one species of minke whale was thought to exist; all minke whales were referred to as Balaenoptera acutorostrata. Morphological and genetic evidence of a second species accumulated through the last quarter of the twentieth century, and the Antarctic minke whale, B. bonaerenis, came to be fully recognized in the late 1990s. Based on genetic data, the two species are hypothesized to have diverged less than 5 million years ago in the Southern Hemisphere. In both species, the rostrum is very narrow and pointed and there is a single ridge on the head. The dorsal fin is relatively tall and falcate and is located relatively far forward on the posterior one-third of the body. The average length of the common minke whale in the North Atlantic at physical maturity has been estimated variously at about 8.5–8.8 m in females and 7.8–8.2 m in males. The skull is larger in B. bonaerensis than in both northern and southern forms of B. acutorostrata. Common minke whales are noted for their curiosity about ships, often coming from afar to cross the bow or run with the vessel for minutes or hours. They are difficult to spot at a distance because of their small inconspicuous blow and brief surfacing behavior. Single animals are often seen and groups are usually small, consisting of two or three individuals, although larger aggregations of up to 400 may form on occasion in high latitudes. Differential migration by sex and age leads to segregation by sex and breeding condition. Mating behavior has not been directly observed.