Minke Whale 

	Minke whale Petit rorqual Balaenoptera acutorostrata Other names: little piked whale, lesser rorqual

Description

• The smallest baleen whale in the St. Lawrence

• Slender body, dark back

• Flattened, pointed head

• Ventral pleats extend from the throat to just behind the pectoral fins

• Narrow, pointy pectoral fins crossed by a large white band

• Falcate dorsal fin

When it surfaces: Rarely visible, its blow can attain a height of two metres. Head and dorsal fin appear almost simultaneously.

An agile and dynamic swimmer with a voracious appetite!

Adopting specific strategies to capture its prey, the smallest of the rorqual whales frequently executes spectacular surface manoeuvres. While in the St. Lawrence, minke whales often swim very near the shore and are also known to breach repetitively! As a result, this species has become a source of pleasure for offshore and land-based whale watchers alike. Previously of little commercial interest to whalers, the minke whale is now the most abundant of the great whales on a planetary scale. Ironically, this abundance has since made it the primary target of countries that continue to commercially and ³scientifically² hunt whales.

Population, range and habitat

In the St. Lawrence: The minke whale frequents the coastal waters of the St. Lawrence Gulf and Estuary to feed from March to December. Its presence in the Estuary is particularly manifest at the head of the Laurentian Channel, between Tadoussac and Les Bergeronnes, and at the mouth of the Saguenay River where it remains plentiful from July to early September. Certain individuals regularly travel approximately a dozen nautical miles upstream into the Saguenay Fjord. Aerial surveys carried out by Fisheries and Oceans Canada in 1995 and 1996 resulted in a Gulf herd estimate of 1000 minke whales, excluding the Estuary; this study did not take diving animals into account.

Migration: Seasonal movements are not well known. Observations and acoustic recordings carried out using a U.S. Navy surveillance system suggest that minke whales move southwards to the West Indies from November to May. In the spring they swim past Bermuda and along the U.S. East Coast to return to their summer feeding grounds, without ever gathering in herds.

Worldwide: St. Lawrence minke whales are part of the Canadian East Coast stock, estimated at 4000 head. This stock is one of four in the North Atlantic. The combined total North Atlantic population is estimated at 200 000 head. Minke whales are found in all of the world¹s oceans, from the Tropics to ice-free Polar Regions. Northern Hemisphere minke whales are distinct from the dwarf minke whale sub-species that inhabits the Southern Hemisphere. The Antarctic minke whale is a distinct species that presents various physical and genetic differences.

Behaviour

Feeding: In summer, the minke whale spends half of its time hunting and feeding. It is a gulp feeder and eats planktonic crustaceans (krill) and small, schooling fish such as herring, capelin and sand lance. Many minke whales demonstrate site fidelity, returning every year to a specific territory where they become specialized in certain types of feeding ploys. The minke whale can be frequently observed surface feeding: performing characteristic manoeuvres and displaying distended, pink throat pleats. It swims in circular, elliptical or hyperbolic trajectories using currents, rock walls and sometimes even ship¹s hulls to trap prey. It also leaps out of the water and falls noisily on its belly or side (lateral or ventral arcs). Different tactics are chosen based on prey density and species. Some minke whales develop exclusive strategies. A good example of this is Loca¹s characteristic ³frog leap² at the mouth of the Saguenay.

At the surface: A minke whale will generally breathe two to three times between dives. It arches its back sharply before diving deep and does not bring its tail above the surface. Minke whales are known to breach vertically, falling back either on their backs or bellies. To the astonishment of surprised whale watchers, these whales may breach several dozen times in a row with short intervals between bouts. They are occasionally curious about boats and have been known to surf in the wakes of larger vessels.

While diving: Minke whale diving behaviour is not well documented. Its dives do not likely exceed 100 m; its prey tends to swim between the surface and this depth. Dive times have a tendency to be a short two to three minutes, but can be as long as 20 minutes.

Social behaviour: Due to segregation, based on gender, age and reproductive fitness, minke whale social organization tends to be quite complex. Males migrate to northern, offshore, North Atlantic waters during summer, females prefer coastal waters further south and juveniles can be found at even lower latitudes. Thus, most St. Lawrence Estuary minke whales are female. They tend to be solitary. Even in areas where prey is abundant and as many as 30 or even 60 individuals are present, no stable associations have been noted. However, they may pair up for a very brief period of time of say two to four breathing sequences. Since 2006, ORES researchers have noted even longer and more frequent associations in the Saguenay‹St. Lawrence Marine Park, with the occasional formation of trios.

Vocal behaviour: The minke whale emits low-frequency sounds in the 80 to 200 Hz range. Its repertoire is made up of vocalizations of decreasing frequencies. According to one study, they may also produce series of high frequency (7500 Hz) clicks. Minke whales vocalize less than fin whales in the Estuary.

Reproduction

Female minke whales reach sexual maturity between five and seven years of age, males between three and six. Mating takes place from January to May. Gestation lasts 10 months and calving takes place from November to March. Nursing lasts four to five months. Cow/calf pairs split up as soon as calves are weaned; this usually occurs before they arrive on their summer feeding grounds. The minke whale mother/calf bond is the shortest of all mysticete whales.

About scientific research

The ORES research team studies minke whale behaviour in the St. Lawrence. This research group has been curating a catalogue of 266 individuals, photo-identified by the shapes of their dorsal fins and the presence of marks and other distinctive characteristics, since 1998. Nevertheless, certain aspects of their lives remain unknown; research in the St. Lawrence is more focused on species at risk.

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