Minke Whale (Balaenoptera acutorostrata)

	Video: Minke Whale & the "Boing" Sound NMFS Southwest Fisheries Science Center
	Did You Know? · The scientific names for minke whales translate to: "winged whale" (Balaenoptera), "sharp snout" (acutorostrata), and "Buenos Aires" (bonaerensis). · Minke whales received their common name from a Norwegian novice whaling spotter named Meincke, who misidentified the species while at sea. · In Antarctic waters, minke whales compose the majority of killer whales diets (up to 85%).

	Minke whale (Balaenoptera acutorostrata) Photo: Howard Goldstein, courtesy of Scripps Institution of Oceanography/ UCSD and RV Roger Revelle

Status
MMPA - Minke whales, like all marine mammals, are protected under the MMPA.

Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Balaenopteridae
Genus: Balaenoptera
Species: acutorostrata

Species Description
Minke whales are members of the baleen whale family and are the smallest of the "great whales" or rorquals. The taxonomy of minke whales is complex because there are at least two recognized species: the northern or common minke whale (Balaenoptera acutorostrata) and the Antarctic minke whale (Balaenoptera bonaerensis). The dwarf minke whale "form" (Balaenoptera acutorostrata subspecies/ allospecies) is considered a possible third species (which has not received an official scientific name). There are several other subspecies as well. The northern minke whale is divided into two distinct subspecies, Balaenoptera acutorostrata scammoni in the North Pacific and Balaenoptera acutorostrata acutorostrata in the North Atlantic. Also, a little known population of minke whales may exist in Sri Lankan waters, recognized as Balaenoptera acutorostrata thalmaha (Jefferson et al. 2008).

The minke whale is the smallest baleen whale in North American waters. These rorquals have a relatively small, dark, sleek body that can reach lengths of up to about 35 ft (10.7 m) and weigh up to 20,000 lbs (9,200 kg). Females may be slightly larger than males. Minke whales have a fairly tall, "falcate", "dorsal" fin located about 2/3 down the animal's back. The body is black to dark grayish/brownish in color with a pale chevron on the back behind the head and above the flippers and a white underside, giving it a counter-shading appearance. Calves are usually darker in coloration than adults.

Minke whales vary in body size, patterns, coloration, and baleen, based on geographical location. They may vary individually as well. Northern minke whales are distinguished from other rorquals by their relatively small size and a well-defined white band located on the middle of their dark pectoral flippers. On each side of their mouths are 230-360 short, white/cream colored baleen plates, and 50-70 ventral pleats are located underneath the animal.

Dwarf minke whales are considered a subspecies of the northern minke whale, but have a much different range and distribution. They are significantly smaller in size at all life stages, growing up to lengths of about 26 ft (7.8 m) and weighing up to 14,000 lbs (6400 kg). Some of this species' baleen plates have a thin black border. Dwarf minke whales can be distinguished from other minkes by a bright white patch on the upper part of the dark pectoral fin that extends up towards the shoulder and back area. They also have a dark "half-collar" that wraps around the head and reaches the throat grooves.

Antarctic minke whales have 200-300 baleen plates on each side of their mouths. Their pectoral flippers are usually solid gray in color with a white leading edge, and the noticeable band of the northern and dwarf form is generally absent. Unlike other minke whales, the coloration of this baleen is asymmetrical, with fewer anterior white baleen plates on the left side than on the right, and the rest being dark gray in color. They also have 22-38 ventral pleats located on the underside of the animal.

Minke whales are often recognized in the field by surfacing snout first, a small, weak, but visible, bushy blow that is about 6.5-10 ft (2-3 m) high, and because they do not display their flukes when diving. When surfacing, they have a quick fluid movement, which creates spray (sometimes described as a "roostertail") when traveling at high speeds. Before deep dives, they may arch and expose much of their back and body during high rolls above the surface. These whales are capable of diving for at least 15 minutes, but regularly submerge for 6-12 minutes at a time. Minke whales are often active at the surface, and are commonly seen "breaching". They are frequently observed "spy hopping" in areas of movable ice (floes and pack) in the Arctic and Antarctic. At sea, these animals may be curious and approach vessels, especially those that are stationary.

These baleen whales are usually sighted individually or in small groups of 2-3, but there are reports of loose aggregations of up to 400 animals associated with feeding areas in higher latitudes. The segregation and distribution of these whales suggests a complex social and population structure, but less is known about the populations in the Southern Hemisphere.

Minke whales feed by side-lunging into schools of prey as well as gulping large amounts of water. Sea birds, attracted to the concentrated prey just below the surface, are sometimes associated with minke whale feeding and foraging. Minke whales opportunistically feed on crustaceans (e.g., krill), plankton (e.g., copepods), and small schooling fish (e.g., anchovies, dogfish, capelin, coal fish, cod, eels, herring, mackerel, salmon, sand lance, saury, and wolfish) (Reeves et al. 2002). In the Southern Hemisphere, krill constitutes the majority of the diet for the Antarctic species, and krill and myctophid fish for the dwarf form.

Minke whales are known to vocalize and create sounds that include "clicks," "grunts," "pulse trains," "ratchets," "thumps," and recently discovered "boings." These distinct vocalizations can vary depending on species, geographic area, and are very helpful in studying and understanding these animals.

Minke whales become sexually mature at around 3-8 years of age (7-8 years for Antarctic minke whales), which is about when they reach 23 ft (7 m) in size. Mating and calving most likely takes place during the winter season. After a gestation period of 10-11 months, females give birth to a single calf that is about 8-11.5 ft (2.4-3.5 m) in length and weighs 700-1,000 lbs (318-454 kg). The calf is weaned from lactation after 4-6 months. The reproductive interval for females is estimated at 14 months, but calving may occur annually (Shirihai and Jarrett 2006). Mother-calf pairs are usually sighted in the lower latitudes of the wintering grounds, but are much rarer in the higher latitude summer feeding grounds. The estimated lifespan of these cetaceans may be up to 50 years.

Minke whale
(Balaenoptera acutorostrata)
Photo: Howard Goldstein, courtesy of Scripps Institution of Oceanography/ UCSD and RV Roger Revelle

Habitat
Minke whales prefer temperate to boreal waters, but are also found in tropical and subtropical areas. Minke whales feed most often in cooler waters at higher latitudes. These whales can be found in both coastal/inshore and oceanic/offshore areas.

Distribution
The distribution of minke whales is considered cosmopolitan because they can occur in polar, temperate, and tropical waters in most seas and areas worldwide. Minke whales, like some other species of cetaceans, migrate seasonally and are capable of traveling long distances. Some animals and stocks of this species have resident home ranges and are not highly migratory. The distribution of minke whales varies by age, reproductive status, and sex. Older mature males are commonly found in the polar regions in and near the ice edge, and often in small social groups, during the summer feeding season. Mature females will also migrate farther into the higher latitudes, but generally remain in coastal waters. Immature animals are more solitary and usually stay in lower latitudes during the summer. In U.S. waters, minke whales in Alaskan waters are migratory, but animals in the inland waters of California/Oregon/Washington are considered "residents" because they establish home ranges.

Northern minke whales have a widespread distribution in the Northern Hemisphere, and are found throughout the northern Atlantic and Pacific Oceans. Their range extends from the ice edge in the Arctic during the summer to close to the equator during winter.

Dwarf minke whales have a circumpolar distribution in the Southern Hemisphere (reported as far south as 60-65° S), especially during the summer months, but are more common in temperate and warmer waters of middle and lower latitudes. They are frequently reported in areas off of Australia (such as the Great Barrier Reef), South America and South Africa. The distribution of the Antarctic and dwarf minke species partially overlaps, mostly in the lower latitudes of the Antarctic minke's range (in the Southern Ocean). The dwarf minke form in this area is considered more "coastal" and generally present earlier in the year than the "offshore" Antarctic species.

The Antarctic minke whale also has a circumpolar pelagic distribution in the Southern Hemisphere and has been reported as far south as 78° S in the Ross Sea during the austral summer. In the southern Atlantic Ocean, it is usually found between 20°-65° S. During this season, immature individuals generally don't travel past 42° S. These whales migrate far distances seasonally, feeding in and around the ice edge during the summer and moving to mating/calving grounds during the winter (7° S- 35° S) (Shirihai and Jarrett 2006). There is some evidence that these whales may travel to and even cross the equator, after one specimen was reported in waters off Suriname.

Population Trends
For management purposes, minke whales inhabiting U.S. waters have been divided into four stocks: the Alaska Stock, the Canadian Eastern Coastal Stock, the California/Oregon/Washington Stock, and the Hawaii Stock. The estimated population of minke whales in Alaska and the Hawaiian Islands is unknown. The California/Oregon/Washington population is estimated to be 500-1,000 animals, and the in Canadian Eastern Coastal population is estimated to be 2,500-3,000 animals. There are insufficient data to determine the population trends for this species in U.S. waters.

Minke whales are the most abundant rorqual in the world, and their population status is considered stable throughout almost all of its range (especially when compared to other species of large whales). There are an estimated 185,000 minke whales in the Atlantic, and 510,000-1,400,000 in the Southern Hemisphere. Minke whale populations in the western North Pacific and the northeastern North Atlantic may have been reduced by as much as half due to commercial whaling practices; but due to the overexploitation of larger rorqual species by commercial whaling, minke whales may have prospered from the lessened competition and increased availability of food resources. Two stocks recognized by the International Whaling Commission (IWC) in the North Pacific, the J-stock (East China Sea, Sea of Japan, and Yellow Sea) and O-stock (Pacific waters and Sea of Okhotsk), are in decline and considered threatened. The eastern North Pacific animals are not considered threatened because they were not commercially harvested, except for a very small number taken for subsistence by Alaska Natives. Recently, the estimated population of minke whales has come into question, and it is possible that some stocks of minke whales may be depleted due to modern whaling and hunting.

Threats
Minke whales have been exploited by whalers since at least the 1930s, but were previously overlooked by hunters due to their relatively small size. Since these whales have been targeted by commercial whalers, several thousand have been hunted in the Northern Hemisphere and at least 100,000 have been killed in the Southern Hemisphere. In the past, these whales have been commercially hunted by China, Iceland, Korea, Russia and Taiwan. Today, they are still taken by whaling countries such as Greenland, Japan and Norway as a source of food and for scientific research. Minke whales have also been hunted by native peoples for subsistence purposes.

Due to their curious nature, dwarf minke whales are easily approachable and subject to whale watching and diving operations off of eastern Australia. This approachability may lead to more human and vessel interactions with these animals. Habitat disturbance and vessel strikes are possible threats to these species.

Minke whales have been reported as incidentally taken in various fishing gear. They have been incidentally taken in groundfish trawls in Alaska, in drift and set gillnets off California/Oregon/Washington, and in numerous fisheries, such as driftnets, gillnets, herring weirs, lobster traps, tuna purse seine nets, and various other cables and lines in Northeast and Mid-Atlantic U.S. and Canadian waters.

Underwater sounds and anthropogenic noise are an increasing concern for baleen whales, such as minke whales, which use low-frequency sounds to communicate with one another.

Conservation Efforts
The International Union for Conservation of Nature and Natural Resources (IUCN's) Red List of Threatened Species considers the northern minke whale to be "Lower Risk Near Threatened" and the Antarctic minke whale to be "Lower Risk Conservation Dependent."

The Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES) , prohibits international trade of minke whale products, despite the efforts of some whaling nations.

In 1997, NMFS developed the Atlantic Large Whale Take Reduction Plan (ALWTRP) to reduce the level of serious injury and mortality of three strategic stocks of large whales (North Atlantic right, humpback, and fin) in commercial gillnet and trap/pot fisheries. The measures identified in the ALWTRP were also intended to benefit minke whales, which are not designated as a strategic stock, but are known to be taken incidentally in gillnet and trap/pot fisheries. The ALWTRP consists of both regulatory and non-regulatory measures, including broad-based gear modifications, time-area closures, and extensive outreach efforts.

Regulatory Overview
This species is protected under the Marine Mammal Protection Act of 1972, as amended.

Key Documents
(All documents are in PDF format.)

Title	Federal Register	Date
Atlantic Large Whale Take Reduction Plan	64 FR 7529	02/16/1999
Stock Assessment Reports	n/a	various

More Information

References:

Reeves, R. R., P. A. Folkens, et al. (2002). Guide to Marine Mammals of the World. New York, Alfred A. Knopf. p.212-221.
Jefferson, T. A, M. A. Webber, and R. L. Pitman. (2008). Marine Mammals of the World, A Comprehensive Guide to their Identification. Amsterdam, Elsevier. p. 59-65.
Shirihai, H. and B. Jarrett (2006). Whales, Dolphins and Other Marine Mammals of the World. Princeton, Princeton University Press. p.62-68.