Minke whale biology

Minke whales grow to a maximum length of 30ft and weight of 10 tons. The minke whale has a  distinct narrow, and pointed rostrum with a single prominent dorsal head ridge. Minke whales  are slender with a prominent dorsal fin located on the rear third of the body. Their grooved throats allow an accordion-like distension during feeding. Thus they are capable of taking in many gallons of prey-laden water into their mouths. The 230-360 baleen plates positioned on each side of the upper jaw are then used to strain water out of the mouth, trapping prey inside. Each plate is about 20cm in length and 12cm in width at the base. 

Coloration is dark gray on the back and white on the ventral surface. The color boundary on the flank is diffuse, with swaths of gray and white extending from the underside to the flanks (lateral body pigmentation). White patches are found in the middle third of the pectoral fins. 

The second smallest of the baleen whales, minke whales consist of two species, and three forms. The southern minke whale (Balaenoptera bonaerensis) is found exclusively in the Southern Hemisphere and lacks the characteristic whale flipper patch. The common minke whale (Balaenoptera acutorostrata) consists of minke whales in the Northern Hemisphere and the dwarf minke whale, which is found in the Southern Hemisphere.

North Atlantic & Pacific minke whale distribution (Balaenoptera acutorostrata)

Southern Hemisphere minke whale distribution (Balaenoptera bonaerensis)

 
Dwarf minke whale (Balaenoptera acutorostrata)

In the Northeast Pacific, minke whales feed on variety of small schooling fish such as herring, capelin and sandlance in addition to a variety of zooplankton. In general, they feed on whatever is locally abundant at the time. In the Southern Hemisphere krill forms a major part of the minke whale diet. 

Prey species vary in distribution and behavior, thus minke whales exhibit different feeding behavior which maximize feeding success. 

As with other closely related species, minke whales are classified as "gulpers" in which the whale lunges at the prey – often at high speeds with its mouth open and throat grooves extended. The mouth is then closed expelling the engulfed water through the baleen plates and then the trapped prey is swallowed. This behavior occurs either at, or below the surface. The exact method of trapping an individual prey school varies by location and individual. In the San Juan Islands, some individuals search for, chase and trap their own prey. Other individuals prey upon fish schools trapped and congregated at the surface by diving birds. 

Minke whales make the weirdest sounds. They are sort of metallic and have been called "Star Wars" sounds. For the longest time, we did not think they vocalized, but Jason Gedamke recorded vocalizations from dwarf minke whales off the Great Barrier Reef and Shannon Rankin and Jay Barlow recorded similar sounds from  minke whales north of the Hawaiian Islands, during what would be their breeding season, and in the area that would be their breeding grounds. This spatial and temporal correlation was similar to that of the sounds Jason recorded.



Distribution and stocks of minke whales in the Northeast Pacific

The International Whaling Commission (IWC) has identified three stocks of minke whales in the North Pacific Ocean. Two stocks are found in the Western North Pacific. These stocks consist of The Sea of Japan/East China Sea Stock and the West Pacific/Sea of Okhotsk Stocks. The third stock is called the Remainder Stock and consists of whales east of 180ºW longitude. The IWC made no further stock separations within the Remainder Stock. 

 

Approximate distribution of minke whales in the eastern North Pacific (shaded area). 

Recently, the U.S. National Marine Fisheries Service subdivided the eastern part of the Remainder Stock into an Alaskan Stock, a Hawaiian Stock and a California-Oregon-Washington (CA-OR-WA) Stock.

Minke whales are common in the Bering Sea, Central and Western Aleutian Islands and are thought to be migratory, and these comprise the Alaska stock. The Hawaiian stock is either a separate stock, or the southern extension of the Alaskan Stock. The only sightings in Hawaiian waters are in winter, suggesting these are Alaska minkes on their winter grounds. 

 


The CA-OR-WA stock is 'resident', consisting of small, and possibly isolated populations. We plan to test this 'isolation hypothesis'. Further, we hypothesize the northern extension of this stock boundary should include coastal waters of British Columbia, Southeast Alaska, Gulf of Alaska and Eastern Aleutian Islands. This extension is hypothesized because of the low numbers of individuals observed, consistent area of habitation and year round sightings. These are the same parameters used to designate the CA-OR-WA stock. See the "New Research" section for more information. 

Minke whale sightings from aerial & shipboard surveys. Outer bold line is boundary of survey and dashed line is US EEZ boundary.

The size of the CA-OR-WA stock is small (1,019 c.v. = 0.73). In the same area, the estimated number of humpback whales is 1,034 (c.v.= 0.31) and blue whales is 1,744 (c.v.=0.28).  Both humpback and blue whales are considered endangered. However, unlike their larger cousins, minke whales have never been killed in either commercial or subsistence whaling operations, so the reason for the small size of CA-OR-WA stock remains unclear.