Minke Whale (Balaenoptera acutorostrata)

 

Description & Behavior

There are two species of minke whales: minke whales, aka Common or Northern minke whales, Balaenoptera acutorostrata (Lacépčde, 1804, acutorostrata means 'sharp snouted') and Antarctic or Southern minke whales, Balaenoptera bonaerensis (Burmeister, 1867).

Minke whales are the smallest of the baleen whales with 50-70 throat grooves. They are part of the largest group of baleen whales called the rorquals (Family Balaenopteridae, the family that includes: blue whales, Bryde's whales, fin whales, humpback whales, minke whales, and Sei whales). These long, slender whales are much more streamlined than other whales. They have a pointed snout that is distinctively triangular, narrow, and pointed (hence its nicknames "sharp-headed finner" and "little piked whale"), paired blowholes, and a broad, flat rostrum (upper part of the head). The throat grooves, in addition to streamlining the shape of the whale, allow the throat area (called the cavum ventrale) to expand tremendously during feeding.

Minkes are the most abundant baleen whale and have a characteristic white band on each flipper (this is absent on the southern minke whales though), contrasting with its very dark gray top colour, sometimes with pale trapezoidal stripes behind their flippers on the top. They have 2 blowholes, like all baleen whales.

Minke whales grow to be about 7.8-9 m long, weighing about 5,400-6,800 kg. Females are about 0.6 m longer than males, as with all baleen whales. The largest minke whale measured was about 10.5 m long weighing 8,600 kg.



There are three subspecies of common or northern minke whales, B. acutorostrata:

1. North Atlantic minke whale, B. acutorostrata acutorostrata (Lacépčde, 1804)
2. North Pacific or Scommon's minke whale, B. acutorostrata scammoni (Deméré, 1986)
3. dwarf-form or dwarf minke whale, B. acutorostrata subsp

Minke whales are stocky, having a layer of blubber several inches thick. They have 50-70 throat grooves, running from the chin to the mid-section. The minke whale has two long flippers (up to 1/8 of the body size), a small dorsal fin, and a series of small ridges along the its back near the flukes (tail). Minke whales either travel singly or congregated in small pods of about 2-3 whales. Minke whales can dive for up to 20-25 minutes, but usually make shorter dives, lasting about 10-12 minutes. Just before diving, minke whales arch their back to a great degree, but the flukes do not rise out of the water. At rest, minke whales spout (breathe) about 5-6 times per minute. The spout of the minke whale is a very low, almost inconspicuous stream that rises up to 2 m above the water. Minke whales begin exhaling before they reach the surface, which minimizes the blow. Minke whales makes very loud sounds, up to 152 decibels (as loud as a jet taking off). They make series (trains) of grunts, thuds, and raspy sounds, usually in the 100-200 Hertz range. These sounds may be used in communication with other minke whales and in echolocation .


World Range & Habitat

Range Description: The Common Minke Whale is a cosmopolitan species found in all oceans and in virtually all latitudes, from 65°S to 80°N. In parts of its range it is very abundant, in other parts much less so. Its migration patterns are poorly known. It occurs in the North Atlantic, the North Pacific, and the Southern Hemisphere, but is not known from the northern Indian Ocean.

North Atlantic
In summer, Minke Whales are common throughout the northern North Atlantic as far north as Baffin Bay, Greenland Sea, Svalbard (Norway), Franz Josef Land and Novaya Zemlya (Russian Federation), and as far south as 40°N (New Jersey) on the US east coast (Anon. 2005a), and as far south as the Hebrides (northwest British Isles) and the central North Sea in the east. In the mid-Atlantic summer concentrations of minke whales occur to at least as far south as 50°N (Sigurjónsson et al. 1991). It is likely that at least a part of the Minke Whale population over-winters in the summer range, but there has been very little observation effort in winter to confirm this.

Minke Whales also occur south of this range in the South-eastern North Atlantic, but with no obvious seasonality, and are not common, with the exception of the Canary Islands, where they appear to be frequent year-round (Van Waerebeek et al. 1999). There have been occasional sightings (Aguilar et al. 1983) and strandings (Van Waerebeek et al. 1999) off Spain and Portugal, Western Sahara, Mauritania and Senegal. Minke whales are rare in the Azores and not recorded from Madeira. The minke whale is considered a “visitor species” in the Mediterranean (average <1 record per year) with one vagrant recorded in the Black Sea (Reeves and Notabartolo di Sciara 2006).

There are very few winter records, but a summary by Mitchell (1991) indicates that they do occur in winter near Bermuda, the Bahamas and the Antilles, and the US coast south of 40°N. Ten strandings have been recorded in the Gulf of Mexico (Jefferson and Schiro 1997) but hardly any live sightings. A Norwegian winter expedition sent to the tropical Atlantic in 1989/90 to “find the breeding grounds of the minke whale” encountered just two minke whales, at 20°N and 10°N off West Africa in December (Folklow and Blix 1991).

North Pacific
Minke whales occur in summer right across the North Pacific north of about 30°N in summer, with a tendency for the distribution to shift northward in high summer. They are particularly abundant in the Okhotsk Sea in August (Miyashita et al. 1995), and also occur in the Bering Sea, around the Aleutian Islands and in the Gulf of Alaska (Moore et al. 2002, Zerbini et al. 2006) and the Chukchi Sea (Ivashin and Votrogov 1981). In the eastern North Pacific, there appears to be a year-round population off California and Baja California and in the Gulf of California, and minke whales occur in summer off Oregon, Washington and British Columbia (Anon. 2003). They have been seen off Hawaii but are not common there (Anon. 2005b).

In the western North Pacific, there are at least two distinct subpopulations: the so-called “J stock,” an autumn-breeding population that occurs in the Yellow Sea, East China Sea and Sea of Japan, with some penetration into the Okhotsk Sea in summer; and the O-stock which, like most baleen whales, breeds in winter, and occurs in summer in the north-western Pacific, including the northeastern coasts of Japan, and in the Okhotsk Sea (Omura and Sakiura 1956, Kato 1992).

The winter distribution is poorly known. Japanese expeditions to look for wintering grounds in the southwestern North Pacific during 1993-95 failed to locate any minke whales (Miyashita et al. 1996). The timing of the arrival of minke whales in Korean and western Japanese waters is suggestive of migration from the south in spring and return in autumn (Ohsumi 1983). The wintering area in the eastern North Pacific has been identified acoustically to be primarily between 15 and 35 degrees N latitude (Rankin and Barlow 2005).

Southern hemisphere
Much of the data on the occurrence of minke whales in the Southern Hemisphere is ambiguous with respect to identification as B. acutorostrata or B. bonaerensis, because the two species are partially sympatric. Japanese scouting vessel data indicated high abundance of minke whales in November between 10°-30°S in the central South Pacific and in much of the eastern and southern Indian Ocean down to 50°S (Miyashita et al. 1995), but their species identity is unclear. The limited information available from surveys in low and middle latitudes from the 1987/88 season onwards, when the two species were reliably distinguished, indicates that most of the minke whales are B. bonaerensis (Nishiwaki et al. 1991), probably on route to the Antarctic from (as yet unknown) low-latitude breeding grounds, but also that B. acutorostrata is present in these latitudes.

Dwarf minke whales occur at higher latitudes but are much less common than B. bonaerensis. Of more than 1,700 minke whales taken by Antarctic pelagic whaling from the 1987/88 to the 1992/93 season (when the two species have been reliably distinguished), only 16 were dwarf minke whales (Nishiwaki et al. 2005). One was taken at 65°S and the remainder at between 55-62°S, the northern limit of whaling operations.

In coastal waters, dwarf minke whales have been recorded off most of the South Atlantic coast of South America (Baldas and Castello 1986, Zerbini et al. 1996), in the Beagle Channel (Chile/Argentina) (Acevedo et al. 2005), off South Africa (Best 1985), Australia (Arnold et al. 1987, Bannister et al. 1996, Arnold 1997), New Zealand (Dawson and Slooten 1990), and New Caledonia (Garrigue and Greaves 2001). The most northerly confirmed Southern Hemisphere record is from 2°S, off the northern coast of Brazil (Magalhăes et al. 2007). Three dwarf minke whales were caught in whaling operations off Costinha, Brazil in 1980 (along with 900 Antarctic minke whales) (da Rocha and Braga 1982).
Countries: Native:
Anguilla; Antarctica; Antigua and Barbuda; Argentina; Australia; Bahamas; Bangladesh; Belgium; Bermuda; Brazil; Canada; Cape Verde; Chile; China; Cuba; Denmark; Dominica; Dominican Republic; Ecuador; Faroe Islands; France; French Guiana; Gambia; Greece; Greenland; Guadeloupe; Iceland; Indonesia; Ireland; Israel; Italy; Japan; Korea, Democratic People's Republic of; Korea, Republic of; Mauritania; Mexico; Morocco; Mozambique; Netherlands; Netherlands Antilles; New Caledonia; New Zealand; Norway; Papua New Guinea; Portugal; Puerto Rico; Russian Federation; Saint Pierre and Miquelon; Senegal; South Africa; Spain; Svalbard and Jan Mayen; Sweden; Taiwan, Province of China; Thailand; Tunisia; Turks and Caicos Islands; United Kingdom; United States; Uruguay; Virgin Islands, British; Virgin Islands, U.S.; Western Sahara


Feeding Behavior

Minke whales, Balaenoptera bonaerensis, (like all baleen whales) are seasonal feeders and carnivores. They sieve through the ocean water with their baleen . They filter out small plankton, krill, and small fish, even chasing schools of sardines, anchovies, cod, herring, and capelin. They have the same diet as blue whales. The baleen plates in their jaws have about 300 pairs of short, smooth plates. Their largest plates are less than 30 cm long and 13 cm wide. Their fine-textured baleen bristles are fringed and white.


Life History

Minke whale breeding occurs mostly in the late winter to early spring while near the surface and in warm waters. Their gestation period is about 10 months and their calves are born near the surface. Their newborns instinctively swim to the surface within 10 seconds for their first breath; helped by their mother using her flippers. Within 30 minutes of their birth, baby minkes can swim. Newborn calves are about 2.8 m long and weigh about 454 kg. Baby minkes, like all mammals, feed on their mother's milk until weaning. Mother minkes and calves may stay together for a year or longer. Minke whales reach puberty at about 2 years of age. Minke whales live for over 50 years. It is estimated that there are about 800,000 minke whales worldwide. The Common Minke Whale occurs in both coastal and offshore waters and exploits a variety of prey species in different areas according to availability. In the Northern Hemisphere some populations migrate to higher latitudes in summer, but minke whales are also found year-round in some areas. With the exception of the Sea of Japan – Yellow Sea – East China Sea population, conception and birth occur in winter. Most animals occur singly, and few in groups of more than two.  In the North Atlantic, studies in the Barents and Norwegian Seas showed that minke whale diet varied greatly between areas and years, being dominated by krill in the northern areas, but by herring or capelin in other areas according to what was most abundant that year, with gadoids being taken when herring and capelin were scarce (Lindstrřm and Haug 2002). In the North Sea the diet consisted almost exclusively of sandeel (data from one year only). Minke whales taken off Iceland in 2003-04 contained mainly sandeel, with some capelin and gadoids (Víkingsson et al. 2006). Minke whales caught off Newfoundland during 1966-72 contained mainly capelin (Mallotus villosus) (Mitchell 1974). In the Northwest Pacific, Lindstrřm et al. (1998) found that krill Euphausia pacifica dominated the diet in coastal areas and in the Okhotsk Sea, while in the offshore Pacific, Pacific saury Cololabis saira dominated.

Systems: Marine


Conservation Status & Comments

The story of this whale's name illustrates its blighted history. Minke was an 18th-century Norwegian whaler, infamous for regularly breaking the rules concerning the sizes (and therefore species) of whales that he was permitted at that time to hunt. Soon all the small whales became known as "Minke's whales". Eventually, it was formally adopted as the name for this small species. In fact, because they are such a small whale, the whaling industry generally ignored the minkes until quite recently. As the larger whales became more scarce (and gained protected status), so minke whales became more economically attractive. In the North Atlantic, from the 1920s, whaling for this species has been conducted along the coast of Norway. When whale populations dwindled in the late 1940s, the International Whaling Commission (IWC) was established to manage whale stocks. The IWC announced how many whales could be taken in any year, however, populations continued to decline. In 1985-1986 a worldwide moratorium on whaling was put in place, banning all whaling. Norway, however, "took out a reservation", meaning that they could continue by IWC rules to legally hunt North Atlantic minke whales and, in 1993 and 1994, they killed several hundred. This has caused great dismay in other countries, including the U.K., who have officially objected to this hunt. In UK waters it is illegal to intentionally kill, injure, capture or harass any species of whale or dolphin. However, there is little in international law that can be done about hunting, except control of exports which is covered by CITES (the Convention for International Trade in Endangered Species). This is important because the main consumers of whale meat are still the Japanese and, if Norway could legally export whale meat to Japan, this might further promote whaling.

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