Minke Whale (Balaenoptera acutorostrata)

IDENTIFICATION

Size
– to a maximum length of 10 metres

Colour
– black or dark gray on the back and white on the belly and the undersides of the flippers
– often have a gray stripe or ‘chevron’ on the side by the flipper
– distinctive white ‘bands’ on the pectoral flippers

Dorsal fin
– tall relative to overall size of animal
– curved towards the back
– usually the fin becomes visible at the same time as the blow

Blow
– low, bushy and usually inconspicuous

Tail fluke
– never seen, dives without showing tail fluke.

Surface behaviour
– usually very inconspicuous; aerial behaviours are very rare

Group size / social behaviour
– usually solitary, avoids boats.

Other characteristics
– smallest baleen whale in the North Pacific (comparable in size to killer whales)
– rostrum (tip of head) is very pointed

Can be confused with
– humpback whale – but is significantly smaller and more streamlined, with relatively small flippers.
– about the same size as a killer whale, but lack of white patches, solitary nature and inobtrusive behaviour will distinguish minke whales from a distance.
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NATURAL HISTORY

Until recently the minke whale, found in all oceans of the world, was considered to be just one species.  Recently, however, the Antarctic minke (Balaenoptera bonaerensis) has been classified as a separate species from the common minke (Balaenoptera acutorostrata).  Within the common minke species, three subspecies are now recognized.  In the north Pacific they are B. a. scammoni.  The north Pacific minke is divided further into stocks by the International Whaling Committee: two in the north west Pacific (Sea of Japan/East China sea stock, Western Pacific/Sea of Okhotsk) and then a ‘remainder stock’ that encompasses all of the minkes east if 180′ W longitude. This remainder has been designated as one due to lack of data, but may actually consist of several stocks.

The minke whale is the second smallest of the baleen whale, and in the north Pacific has been largely under-studied due to its elusive nature.  Minke whales can be hard to research; they are fast, observed swimming at speeds of 30 km/h, and their surfacing can been sporadic and hard to follow.  The ‘blow’ of a minke whale is rarely seen- though smelt easily if upwind of observers, earning this species the nickname ‘stinky minke’.

Until recently, little was understood about north Pacific minke whale migratory patterns.  While animals in the extreme north are thought to be migratory, heading to southern waters in the winter, it was not known if this was the case for populations in the eastern North Pacific. Thanks to a long standing photo identification study done by the Marine Education and Research Society (MERS) in collaboration with researchers on the British Columbian and Washington coasts, it was determined that minkes in this area do indeed migrate. Some minkes were documented to travel as far as 424km north in the spring, and 398km south in the autumn, marking the longest documented migration. It is known that they are moving to warmer waters during the winter months, but there is still much to learn about where they go during this time.

Minke whales are seen to be quite loyal to summer feeding areas and individuals have appeared in the same site year after year.  Minke whales are individually identifiable by colouration and scarring on their dorsal surfaces and flanks, and hopefully further photo-identification will give more answers about their movements and numbers. Photo-identification work is currently being done by the Northeast Pacific Minke Whale Project.  A study done in the Puget Sound area of Washington State has shown that minke whales may have exclusive, adjoining home ranges. This is unknown in other baleen whales.

In the northern hemisphere, minke whales appear to be feeding primarily on small schooling fish such as herring, capelin, sandlance and pilchard.  They may also feed on krill and other zooplankton, which is the staple food for southern hemisphere minkes.  Minke whales capture their prey by lunging through concentrations of fish and krill.  Their throats are pleated, which when expanded allow large amounts of water to enter the mouth/throat cavity.  The saltwater is then expelled and the minke’s short, fringed baleen traps the food.  Minkes are often seen feeding in the presence of bird flocks and may actually target areas where diving birds have previously schooled prey together.  Certain minkes may actually specialize in exploiting these feeding flocks.  The distribution of minke whales in the summer months in the north Pacific seems to be determined by the distribution of their prey and they will be missing from areas where little food is available.

It is estimated that minke whales become sexually mature at 8 years for males, and 7-8 years for females.  Actual mating behaviour between minkes has never been observed and remains unclear.  Breeding and calving grounds in the north Pacific are also unknown.  Females are pregnant for approximately 10 months.  In the waters of British Columbia, minkes are not seen with calves in the summer and it is thought that the mothers and calves may only stay together for 4-6 months.  Weaning and separation are probably complete before the summer months.

The biggest predator of the minke whale is the transient killer whale.  Minke whales attempt to avoid these attacks by fleeing directionally at a high speed.  In attempt to out-swim transient killer whales, minkes will maintain speeds between 15-30km/h for up to one hour.  Killer whales may be able to out sprint the minke, but the long distance endurance of the minke in open water is their best antipredation tactic.  It is when minke whales are trapped in bays or harbours that they are generally unsuccessful in avoiding predation.  Minkes have not been observed physically defending themselves when trapped, choosing other tactics such as beaching themselves.  One such instance took place in the Ganges Harbour of Salt Spring Island in 2002, read about it here.

The minke whale was originally overlooked by commercial whaling until the later half of the 20th century because they were considered too small to be of value.  Because of the decimation in larger baleen whale stocks, and the minke’s apparent abundance, they have since been very heavily targeted by whaling in other parts of the world.  No commercial whaling has happened in British Columbian waters since 1968.

 

 

STATUS IN CANADA

The minke whale is designated as Not at Risk by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

COSEWIC’s assessment of the North Pacific subspecies of the common minke whale (Balaenoptera acutorostrata scammonii) is as follows:
There is no identifiable threat to the subspecies in the eastern North Pacific (there is no whaling; number of deaths from entanglement in fishing gear and ship strikes is not thought to be high enough to cause concern). There is considerable potential for rescue – mainly from United States waters to the north and south; individuals occurring in inshore waters in Canada could constitute a naturally small population.

 

Minke Whale
Minke Whale
Doug Sandilands
Minke Whale
Doug Sandilands
Minke whales are often seen in the presence of large flocks of seabirds
Doug Sandilands
Minke whales are often seen in the presence of large flocks of seabirds
Minke whales breaching are a very rare sight!
Tony Jenkinson
Minke whales breaching are a very rare sight!
Minke whale lunge feeding
John Ford
Minke whale lunge feeding
Transient killer whales attacking a minke whale
Jason Bateman
Transient killer whales attacking a minke whale