Minke whale life history
Morphology and distribution
Common minke whale (Balaena acoutorostrata) Illustration Uko Gorter
Minke whales grow to a maximum length of 30ft and weight of 10 tons. They are slender whales with a prominent dorsal fin located on the rear third of the body. The minke whale has a distinct narrow, and pointed rostrum with a single prominent dorsal head ridge. Their grooved throats allow an accordion-like distension during feeding. 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.
Minke whales are the second smallest baleen whale and 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.
Dwarf minke whale (Balaenoptera acutorostrata)
Southern minke whale (Balaenoptera bonaerensis)
dwarf minke whale gulping (or perhaps yawning!)
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. In the Western North Pacific there are the Sea of Japan/East China Sea Stock and the West Pacific/Sea of Okhotsk Stock. The third stock includes all minke whales east of 180ºW longitude. And is unimaginatively called the Remainder Stock.
The Remainder Stock
In the US the eastern part of the Remainder Stock is subdivided 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. It is likely that whales in the coastal waters of British Columbia, Southeast Alaska, the Gulf of Alaska and the Eastern Aleutians are also part of this stock as they are also observed in low numbers year round and in predictable areas.
There is no clear population estimate for minke whales inhabiting the coastal waters of California, Oregon and Washington. The 2005 NOAA ship survey effort resulted in an estimate of 957 (CV=1.36) but no minkes were seen on effort during the most recent surveys in 2008. Currently the minimum population estimate is 202 and is likely no more than 600.
Minke whales are not listed as "endangered" under the Endangered Species Act and are not considered "depleated" under the MMPA, however NOAA note that the greatest uncertainty in their status is whether entanglement and ship-strike could be reducing this already small population. Minke whales have never been killed in either commercial or subsistence whaling in this region so the reason for the small size of CA-OR-WA stock remains unclear.
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. Prey species vary in distribution and behaviour, 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.
To learn more about the foraging behaviors of minke whales around the San Juans click the link below:
Minke whales make the weirdest sounds. In the North Pacific common minke whales produce a sound called the "boing." This sound had been recorded for many years, but it wasn't until very recently that researchers figured out the source -the minke whale. It consists of a brief pulse at 1.3 kHz, followed by a call at 1.4 kHz that changes frequency slightly over its 2.5 sec duration.
The dwarf minke whale produces a complex and stereotyped vocalization called the "star-wars" vocalization. It spans a wide frequency range from 50 Hz to 9.4 kHz and is composed of distinct and repeated components. Jason Gedamke recorded the strange vocalizations from dwarf minke whales off the Great Barrier Reef while 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.