Fin whale

Identification

The fin whale (Balaenoptera physalus) is very streamlined in appearance but slightly fuller in shape than the blue whale, rounded in the front, but compressed laterally in the tail region with a distinct ridge along the back behind the dorsal fin (hence the name "razorback"). The head is about 1/4 of its body length, or slightly larger in adults, and is markedly triangular in dorsal view and flat with a median crest. The jaw is large and strongly convex laterally, so that when the mouth is closed the lower jaw protrudes slightly beyond the tip of the snout. The dorsal fin is set two thirds of the way along the back, and is up to 60 cm tall, falcate, and often slopes backwards. Its tip may be pointed or rounded. The flippers are slender and relatively short with a pointed tip. The tail flukes are broad (1/5 the length of the body) with a distinct median notch and slightly concave trailing edge.

Colouration is dark grey to brownish black dorsally, grading to pale or white ventrally. The undersides of the flippers and flukes are also white. The head is asymmetrical in colour; mostly dark, but the right lower jaw is white. The body is free of mottling or extensive scarring. Some whales have a pale grey chevron on each side behind the head and there may be a dark stripe running up and back from the eye and a light stripe arching down to where the flipper joins the body.

There are 50 to 100 ventral pleats, from the chin to the umbilicus or slightly beyond the mid line. Each side of the jaw has between 260-480 baleen plates which are also dark on the left and pale on the right and upto 72 cm long and 30 cm wide. The plates have yellow to white fringing fibres, are soft compared to blue whale baleen, and vary from yellowish-white to greyish-white in colour.

Fin whales are fast moving and may swim at speeds of up to 41 km per hour when alarmed, 30 km per hour in short bursts when migrating or cruising, and 2 - 6.5 km per hour when feeding. During migration, it has been calculated that they swim about 90 miles a day.

These whales may dive to depths of over 200 m, which is deeper than either blue or sei whales, and explains why the surfacing, blowing and diving characteristics are different between the species. When fin whales are submerging, the blowholes submerge before the dorsal fin becomes visible. They arch their backs as they dive, but do not usually show their flukes. It is difficult to judge when and where a fin whale will surface.

When moving slowly, a fin whale exposes the dorsal fin soon after the blowhole. However, when surfacing from a deep dive, it emerges at a steeper angle, so that the top of the head surfaces first, blows, submerges the blowhole, and then rolls forward arching the back and dorsal fin high above the surface. 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 last approximately 50 seconds for fin whales feeding at the surface.

The fin whale may side-fluke (a fluke visible at the surface, moving laterally but orientated vertically) and may breach on occasion -- typically landing on the belly -- but may twist in mid-air and land on one side or on the back. These whales have been observed ‘sleeping’ at the surface at night, and have been reported, when feeding, to be slow moving and often so absorbed in feeding that they are largely unaware of approaching boats.

Distribution & Habitat

Fin whales are widely distributed but less common in tropical waters than in temperate waters, and the Arctic and Antarctic oceans. In the lower Bay of Fundy, fin whales are 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. The species does not appear to penetrate as far south into the Antarctic as blue whales and minke whales, and tend to enter and leave the Antarctic feeding grounds after blue whales but before Sei whales.

Natural History & Ecology

After the blue whale, fin whales are the second largest animal on Earth. They can reach lengths of up to 27 m and weights of up to 85 tonnes. In the Southern Hemisphere, females become sexually mature at a length of 19.9 m and males at 19.2 m. Physical maturity is reached at lengths of 22.4 m for females and 20.6 m in males. Breeding peaks in the winter and the gestation period is 11.25 months. Lactation extends over 6 or 7 months. The calving interval is about 3 years, but this has also reduced as a result of exploitation by commercial whaling. Photo-identification studies in the Gulf of Maine indicate that the average time between consecutive births is 2.71 years.

Fin whales feed on planktonic crustacea, fish and cephalopods, although diet varies between areas and seasons. In the Southern Hemisphere, the krill Euphausia superba is the major prey item, although other species of krill and amphipods (such as Parathemisto gaudichaudi) are eaten in lower latitudes and when seasonally abundant. Herring, capelin and other shoaling fish are eaten in both the North Atlantic and North Pacific along with squid, euphausiids and copepods.

Fin whales usually feed using the swallowing technique. They often feed on their sides at the surface, scooping up prey and water in their expanded buccal cavity. The amount of food consumed by fin whales per day has been calculated as 1- 1.5 tonnes in the North Pacific, but as much as 2.8 tonnes in the Antarctic. It has been suggested that the asymmetrical colouring of the head may be used in feeding; observers noting that the white side of the head is usually downwards when feeding on their side.

Social 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, especially on feeding grounds. Although they are more commonly seen in small groups than other rorqual whales (which are often solitary), little is known of fin whale herd behaviour or group composition during the reproductive season in the winter.

Differences in group size may result from the presence of different types of prey in different areas, although geographical segregation by sex or age-class might also influence group size. Observations of fin whales off Newfoundland and Labrador has revealed that the bonds between pairs and groups of fin whale are variable over periods of hours, indicating that long-term pair bonds, presumed by earlier scientists, are probably not common.

Fin whales probably associate with many different individuals, forming fluid associations in feeding areas. Apparent sexual behaviour has been observed on occasions, including excited chases at the surface. Lunging activity, when several whales are present, has been interpreted as antagonistic behaviour in some cases, although it may also represent feeding behaviour.

During migration, fin whales (as with other species of baleen whale) are segregated by sex, as well as age: males migrating first and pregnant females migrating in advance of other sexual classes, with immature whales at the rear.