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Monday, 31 August 2009

Species Spotlight: MINKE

The Minke is split into two distinct species. The Common (Balaenoptera acutorostrata) and the Antarctic Minke (Balaenoptera bonaerensis).

Minke Whale
Common Minke Whale - Balaenoptera acutorostrata

The Minke Whale, also called the Lesser Rorqual, is the name given to two species of marine mammals belonging to the suborder of the baleen whale. The Minke Whale has been catagorised into two species, namely the Common Minke Whale or Northern Minke Whale, as well as the Antarctic Minke Whale or Southern Minke Whale. The Common Minke Whale has two or three subspecies, the North Atlantic Minke Whale, the North Pacific Minke Whale and Dwarf Minke Whale. All Minke Whales form part of the rorqual group, a family that includes the Humpback Whale, the Fin Whale and Blue Whale.

The Minke Whale is the second smallest of all the baleen whales, males measuring an average of 6,9 meters and females 7.4 meters in length upon sexual maturity at age 6 – 8 years of age. Both sexes weigh approximately 4 – 5 tonnes at maturity, but their maximum weight can be as much as 14 tonnes. The Common Minke Whale is distinguished from the other species, by a white band on each flipper. Its body is usually black or dark-grey above and white underneath. Minke whales have a snout that is distinctively narrow and pointed, hence its nicknames ‘sharp-headed finner’ and ‘little piked whale’. Its maximum swimming speed has been measured at 20-30 kilometers per hour. This whale has been known to breathe 3 – 5 times at short intervals before deep diving for 2 – 20 minutes. When resting, they breathe about 5 – 6 times per minute. Their spout is a very low, almost inconspicuous stream that rises about 2 meters above the water, beginning to exhale before they have even reached the surface. Minke Whales make very loud sounds which are used in communication with other whales, as well as for echo-location.

Minke Whales breed mostly in the summer months, with calving taking place every two years. Gestation is 10 to 11 months with babies measuring 2,4 – 2,8 meters at birth and nursing for approximately 5 months.

The total population of the Minke Whales is found to be 103,000. Due to their relative abundance, these whales are often the focus of many whale-watching cruises. They are very inquisitive and will swim very closely to any vessels. Many enthusiasts have even called these whales ‘stinky Minkes’ as it is frequently possible to smell the breath of the nearby whale. Like all baleen whales, Minke Whales are carnivores, sieving their food through the ocean water, filtering out small plankton, krill and small fish. They enjoy chasing small schools of sardines, anchovies and cod.

The Minke Whales were for a long time the target of coastal whaling from countries such as Brazil, Canada, China, Greenland, Japan, Korea, Norway and South Africa. By the early 1970’s, following the over-hunting of larger whales such as the Fin and Blue Whales, the Minke’s attracted the attention of the whalers. Hunting continued until the moratorium was brought out in 1986.

Minke whales typically live for 30-50 years; but in some cases they may live for up to 60 years.

Antarctic Minke Whale - Balaenoptera bonaerensis

There are several differences between the Antarctic Minke Whale and the Common Minke Whale. The Antarctic Minke Whale is slightly larger than the Common Minke Whale, and the Common Minke Whale has a white band in the centre of each flipper. There are also some slight differences in body shape and colouration. The Antarctic Minke Whale is more robust than other large baleen whales, with its rostrum being very narrow and pointed with a single ridge on its head. It has a dark bluish grey back together with a contrasting pale grey belly and white flanks. It has a crescent shaped grey streak running up each side of the animal. Antarctic Minke Whales have asymmetrically coloured baleen, with the right side having a larger number of white plates than the left. They range from 7.2 to 10.7 meters in length and weighing approximately 5.8 to 9.1 tonnes. Females are usually about 1 meter longer than males.

The Antarctic Minke Whale is found in all oceans of the Southern Hemisphere. In summer, it lives close to the Antarctica, but in winter moves further north. Mature Antarctic Minke Whales feed primarily on the Antarctic Krill. It appears they do not feed much while in the breeding grounds of lower latitudes, but when they do feed their diet remains krill based. Krill are pelagic and tend to only occur on the top surface of the Antarctic waters, therefore these whales do not need to dive deep to feed on the oceans floor.

Mating occurs from June to December, peaking in August and September. Gestation lasts about 10 months with calving peaking during late May and early June in the warmer waters north of the Antarctic. Calves are born measuring 2.4 to 2.8 meters in length and while suckling upon their mother, they grow at a rate of about 1 centimeter per day. They are weaned at about 4 or 5 months when the calf has reached approximately 5.7 meters in length. Weaned calves probably feed upon copepods and small fish. Ovulation of the female Antarctic Minke Whale occurs about 4 months after the birth of her calf, which leads to a 14 month calving cycle.

The Antarctic Minke Whales are not very social, tending to swim alone or in pairs. However, large feeding groups of up to 400 individuals may form in the higher latitudes. Young males appear to be more solitary than mature males but have also been known to be curious creatures, often approaching boats from a distance. Male Antarctic Minke Whales reach sexual maturity at about 7.3 meters, females at 7.9 meters and at the age of about 7 to 8 years. These whales have been known to exceed 50 years of age. They are the prey of Killer Whales, with one estimate suggesting that Antarctic Minke Whales comprise of up to 85 percent of the diet of Killer Whales in the Southern Oceans.

This species of whale has undergone extensive population reductions with about 14 600 whales killed off the coast of Brazil, 1113 from South Africa and over 98 200 in the Antarctic feeding grounds between 1957 and 1987. Continued whaling, even at low levels, could seriously reduce the Antarctic Minke Whales population size in years to come.

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