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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.
Western North Pacific Stocks :
The Sea of Japan/East China Sea
Stock
West Pacific/Sea of Okhotsk Stocks
The Remainder Stock is the third stock and consists of
whales east of 180ºW longitude.
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Approximate distribution
of minke whales in the eastern North Pacific (shaded
area). |
The Remainder Stock
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.
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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 are estimated to be
between 600 and 1000 minke whales inhabiting the coastal
waters of California, Oregon and Washington. 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. |
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Minke whale
sightings from aerial & shipboard surveys. Outer
bold line is boundary of survey and dashed line is US
EEZ boundary. |
Feeding
Ecology
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.
Acoustic Behaviour
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.
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