Fin Whale

Balaenoptera physalus

KEY FACTS
Gaelic name: Muc-an-scadain
Length: males about 25 metres; females larger (27 metres)
Weight: up to 80 tonnes
Range: Widely distributed
Threats: Noise and Chemical Pollution

Physical Description
The fin whale is the second largest animal, after the blue whale. Fin whales can reach maximum lengths of up to 27m.  The fin whale is streamlined in appearance, but is slightly fuller in shape than the blue whale. The head is about 1/4 of body length, or slightly larger in adults.

The dorsal fin is set 2/3 of the way along the back, and is up to 60 cm tall. Flippers are slender and relatively short with a pointed tip. Tail flukes are broad (1/5th the length of the body) with a distinct median notch and slightly concave trailing edge.

Fin whales are dark grey to brownish black dorsally, grading to pale or white ventrally. The undersides of the flippers and flukes are also white.

Life span
The life span of a fin whale may be 85 to 90 years. Killer whales occasionally attack fin whales.

Distribution
Fin whales are widely distributed but less common in tropical waters than temperate waters, and the arctic and Antarctic oceans. In the lower Bay of Fundy, fin whales were found to be distributed mainly in shallow areas with high topographic variation. Underwater sills or ledges may be an important feature of fin whale feeding habitat, as are areas of upwelling and interfaces between mixed and stratified waters.

Like other large baleen whales most fin whales migrate annually toward the poles in spring and back to temperate waters in the autumn. Some fin whales in the Northern Hemisphere apparently concentrate in inshore areas in winter, and fin whales may be resident year round in some places, such as the Gulf of California and the Mediterranean Sea.

Behaviour
Fin whales may be found alone or in pairs but often form larger pods of 3 to 20 animals, which may be part of a wider group of hundreds of individuals spread over a wide area.
Fin whales are fast moving and may swim at speeds of up to 41 km per hour when alarmed and 30 km per hour in short bursts when migrating or cruising. During migration it has been calculated that they swim about 90 miles a day.

Fin whales may dive to depths of over 200 m, which is deeper than either blue or sei whales. A series of 2 to 5 blows with 10 to 20 seconds between followed by a longer dive, typically 15 minutes long, is common. Duration of dives ranges from 25 seconds to 15 minutes and mean blow intervals were found to be about 50 seconds for fin whales feeding at the surface.

Fin whales have been observed ‘sleeping’ at the surface at night, and have been reported, when feeding, to be slow moving (2-6.5 km per hour) and often so absorbed in feeding that they are largely unaware of approaching boats.

Breeding
Breeding peaks are the winter and the gestation period is 11.25 months, by a calving interval about 3 years. Lactation extends over 6 or 7 months.

Fin whales become sexually mature at a length of about 19 m in females and about 18 m with males.
The age at sexual maturity has declined in Southern Ocean fin whales (and in some other areas such as Iceland) since the severe depletion in the population by commercial whaling. The age has decreased from 10 years in the 1930’s to 6 or 7 years.

Feeding
Fin whales feed on planktonic crustacea, some fish and cephalopods. The diet varies between areas and seasons.

The amount of food consumed by fin whales per day has been calculated as 1- 1.5 tonnes in the North Pacific, 2.8 tonnes for in the Antarctic, and 0.533 tonnes off the north-east coast of USA.

Current Situation
Pre-exploitation numbers of fin whales were somewhere in the region of 490,000 in the Southern Hemisphere and 58,000 in the Northern Hemisphere. Fin whales have been severely reduced by whaling, which continued in some places until as recently as the 1980’s.

Fin whales have been shown to carry high levels of bioaccumulating pollutants such as heavy metals, PCB’s and other organochlorine compounds; these have been demonstrated to accumulate with age and to transfer between generations via lactation. The effects which can result from pollutants such as these include reproductive and health impairment in other species of marine mammals, and have also been linked with mass die-offs.

Fin whales may also be negatively impacted by noise and disturbance from vessels and other underwater noise, which may mask their social sounds.

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