Common minke whale / Antarctic minke whale

 

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Classification:

Global Population

Description and Natural History

Physical Description
The minke (pronounced "min-key") whale is the smallest member of the family Balaenopteridae. While there has been some confusion about the taxonomy of this species, Rice (1998) suggests that the minke whale should be classified as two species. In the Northern Hemisphere; B.a. acutorostrata can be found in the Atlantic and B.a. scammoni in the Pacific. In the Southern Hemisphere, the Antarctic minke whale, B. bonaerensis, and a distinct population of unnamed "dwarf" minke whales are found.

With the exception of the dwarf minke (which inhabits the Southern Hemisphere but is more closely related, genetically, to its Northern Hemisphere relatives), minkes from the northern and southern hemispheres differ in several ways.

Antarctic minke whales are larger than their Northern Hemisphere counterparts, with females reaching a maximum length of 10.7 meters (35 feet) and males reaching 9.8 meters (32 feet). The maximum weight of adults is about ten tonnes (11 tons).

Northern Hemisphere minke whales reach a maximum length of 9.2 meters (30 feet). Calves in both hemispheres are born at approximately 2.4 - 2.8 meters (7.9 - 9.2 feet) in length and weigh 350 kilograms (770 pounds). The smaller dwarf minke whales reach eight meters (26 feet) in length and calves are born at about two meters (6.6 feet).

All minke whales have a slender, streamlined body with a dark v-shaped head when viewed from above. The snout is narrow and pointed. There is a single longitudinal ridge along the rostrum in front of the blowholes. There are two blowholes, as in all baleen whales, and a straight mouth line. Ventral grooves run from the bottom of the chin to the navel. Baleen plates are short and their color, which varies with geographic location, tends to be lighter at the front and darker toward the back.

The body is dark gray or black on the back and white below, with gray shading extending up each side under, and in front of, the dorsal fin. The dorsal fin is sickle-shaped and situated about two thirds of the way along the body toward the tail.

Minke whales from the Northern Hemisphere have a white band around each flipper, whereas Antarctic minke whales may not have any flipper bands or have bands of irregular color and position. The flippers of dwarf minkes are white at the base and dark at the tip, with a white shoulder patch where the flipper joins the body and dark patches extending in front of the flippers and onto the throat.

Natural History
Minke whales inhabit oceans worldwide but are more common in cooler waters. They can be found offshore but are often seen in coastal and inshore areas entering bays and inlets. They do not "fluke up" (lift their tail fins into the air) when they dive, although they often arch the tail stock high above the water before a long dive.

Although they do not bow ride, they may approach or follow beside boats and will perform acrobatic displays such as spyhopping or breaching.

Minke whales are found in some areas throughout the year but only seasonally in others. It is thought that some populations migrate each year from polar feeding grounds to warmer breeding grounds. In the summer, North Atlantic minkes are found at high latitudes in Ungava Bay, Baffin Bay, Davis Strait, Denmark Strait, Jan Mayen, Svalbard and the Barents Sea.

Wintering grounds are poorly documented but sightings have occurred off the coast of Virginia, south to Dominica in the western North Atlantic, and from the North Sea to the Strait of Gibraltar in the eastern North Atlantic.

North Pacific minke whales summer in waters from the southern Chukchi Sea south to the East China Sea, into the central Pacific and the coast of Baja California. Their winter distribution is also poorly known but extends from the East China Sea and central California almost to the equator.

Antarctic minke whales summer in the Antarctic zone, especially close to the edge of the pack ice, and winter in the north, from the equator to the 35th parallel. They have also been sighted in the Ross Sea in winter.

The "dwarf" minke whale tends to be distributed in the lower latitudes of the Southern Hemisphere with wintering grounds from South Africa, Australia, New Zealand, New Caledonia and the eastern coast of South America from March to December. Scattered records exist from the sub-Antarctic during December to March and the dwarf form has been observed south of 60 degrees south.

Minke whales tend to be solitary or found in small groups, although they may also be found in larger aggregations in areas where prey is concentrated. Minkes feed primarily on krill and small schooling fishes.

There is no agreed-upon population estimate for the Southern Hemisphere minke whale. The International Whaling Commission (IWC) is still considering the status and structure of the different populations of this species. The North Atlantic population (excluding the Canadian east coast) has been estimated at 149,000 individuals, and the Northwest Pacific and Okhotsk Sea population estimated at approximately 25,000.

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Status of the Species

Status
B. acutorostrata is listed as Lower Risk: Near Threatened by the International Union for the Conservation of Nature and Natural Resources (IUCN) and listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). B. bonaerensis is listed as Lower Risk: Conservation Dependent by IUCN and also listed on Appendix I of CITES.

Threats to the Species
The minke whale is the smallest of the large whales and was therefore uneconomical to harvest commercially until the 1920s, by which time all larger whales had been severely depleted. Despite the International Whaling Commission’s 1986 moratorium on commercial whaling, minke whales have become the principal target for whaling by Norway and Japan over the past 20 years.

Since 1993, Norway has been commercial whaling in the Northeast Atlantic under objection to the IWC moratorium. Between 1993 and 2000, Norway landed 3,172 minke whales. Japan has also been whaling under the banner of "scientific whaling."

Between 1990 and 1999, Japan landed a total of 3,751 minke whales from the Antarctic, including some dwarf minke whales.

Between 1994 and 2000, Japan also landed 538 minkes from the North Pacific where the genetically distinct offshore "O" stock and the inshore Sea of Japan/East Sea "J" stock are found. Because the two stocks are visually indistinguishable, individuals from the depleted "J" stock may be taken by Japan, and some are taken as fisheries bycatch by South Korea.

The Scientific Committee of the IWC concluded in 1999 that the genetically distinct "J" stock is "likely to further decline markedly" because of the high level of incidental catches. Meat from the hunt and from fisheries bycatch is sold commercially in both Japan and Korea.

Minke whales may also be threatened by entanglement in fishing gear, collisions with ships, ocean pollution (marine debris, chemical contamination, oil spills and noise) and habitat degradation by coastal development.

International Trade
Listed on CITES Appendix I which prohibits international trade.

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Authors and Sources

Sources
Baker, C.S., G.M. Lento, F. Cipriano, S.R. Palumbi and B.C. Congdon. 1999. North Pacific minke whales on the Japanese markets: species identification, stock estimation and individual exclusion. Working Paper for the Molecular Identification of Whales, Dolphins and Porpoises Workshop. Southwest Fisheries Science Center, La Jolla, California, USA, 14-16 June 1999. Mol ID Working Paper 5.2.1. 6pp

CITES. 2001. Balaenoptera acutorostrata. http://www.cites.org.

CRC Reef Research Centre. 2001. Dwarf minke whale biology.

Discovering Whales. The minke whale. 2001. http://whales.magna.com.au.

IFAW. 2001. Whale kills since 1990.

IUCN. 2001. The 2000 IUCN Red List of Threatened Species. http://www.redlist.org.

IWC. http://ourworld.compuserve.com.

Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine mammals of the world. FAO Species Identification Guide. UNEP, Rome. 320pp.

Rice, D.W. 1998. Marine mammals of the world: systematics and distribution. Special Publication Number 4. The Society for Marine Mammalogy. 231 pp.

WDCS. 2001. Minke whale. http://ourworld.compuserve.com

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