Whales, Dolphins, and Porpoises of the Western North Atlantic Part 10

[Ill.u.s.tration: Figure 14.--Dead blue whales, harpooned and afloat off the stern of a factory s.h.i.+p in the Antarctic (top), and on the deck of a whaling station in western Canada (bottom). In both, note the numerous ventral grooves (from 55 to 85 or more) extending to the region of the navel and sometimes beyond, and the light coloration of the undersides of the flippers. Even though grooves are often present above the flippers, and occasionally even on the side of the head, counts of ventral grooves are usually made between the flippers. (_Photos by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura (top); and G.

C. Pike, courtesy of I. MacAskie (bottom)._)]

FIN WHALE (B)

_Balaenoptera physalus_ (Linnaeus 1758)

Other Common Names

Finback whale, finner, razorback, common rorqual.

Description

Fin whales have been reported to reach 79 feet (24 m). Females are slightly larger than males of the same age.

The back is distinctly ridged towards the tail, prompting the common name "razorback" whale.

The rostrum is narrower and more V-shaped than that of the blue whale and has the same sort of single distinctive head ridge. The top of the head is flat, though slightly less than that of the blue whale.

The dorsal fin is up to 24 inches (61 cm) tall; angled less than 40 on the forward margin, located slightly more than one-third forward from the tail, and appears on the surface shortly after the blow.

All individuals are dark gray to brownish black on the back and sides with none of the mottling present on blue whales and are rarely as heavily scarred as sei whales. Along the back, just behind the head, there is a grayish-white chevron, with the apex along the midline of the back and the arms of the chevron oriented posteriorly, which is sometimes distinctive and may be visible as the animals surface to breathe. The undersides, including the undersides of the flukes and flippers, are white. On the head, the dark coloration is markedly asymmetrical, reaching farther down on the left than on the right side.

The right lower lip, including the mouth cavity, and the right front baleen (approximately one-fifth to one-third) are yellowish white.

Occasionally the right upper lip is also white. The remainder of the plates on the right side and all those on the left side are striped with alternate bands of yellowish white and bluish gray. The fringes of the plates are brownish gray to grayish white.

Natural History Notes

Fin whales are one of the most common baleen whale species in the world and const.i.tute a major portion of the whaling catch. They are reportedly one of the fastest of the big whales (sei whales may be slightly faster) possibly reaching burst speeds in excess of 20 knots, and were not an important commercial species until the comparatively recent development of fast catcher boats and the depletion of blue whale stocks.

A fin whale's blow can be from 15 to 20 feet (4.6 to 6.1 m) tall and has been described as an inverted cone or an elongated ellipse.

Fin whales dive to at least 755 feet (230.1 m). This depth is probably deeper than that of either blue or sei whales, a factor usually reflected in differences among the surfacing, blowing, and diving characteristics of these three species. When they are moving leisurely at the surface, fin whales expose the dorsal fin shortly after the appearance of the blowholes, slightly later than that of the sei whales.

When they are surfacing from a deeper dive, however, they surface at a steeper angle, blow, submerge the blowholes, and then arch the back and dorsal fin high into the air before beginning another long dive. In this species it can be generally stated that the maximum amount of the back in the area of the dorsal fin which is exposed above the surface as the animal sounds is approximately 2 times the height of the dorsal fin. Fin whales do not show their tail flukes when beginning a dive.

Unlike blue or sei whales, fin whales do breach on occasion. When they do leap clear of the water, fin whales usually reenter with a resounding splash, like that made by humpback and right whales and not smoothly, head first, as minke whales often do.

Fin whales are sometimes found singly or in pairs but more often occur in pods of six or seven individuals and many pods consisting of as many as 50 animals may be concentrated in a small area.

Fin whales calve and breed in winter, mostly in temperate waters.

Atlantic fin whales eat a wide variety of foods, including krill, capelin, squid, herring, and lanternfish.

May Be Confused With

Fin whales may be confused with blue whales, sei whales, and, in the southernmost portion of their range, with Bryde's whales. They may be distinguished from the blue whales by differences in overall coloration, coloration and shape of the head, and the size, position, and time of appearance of the dorsal fin at the surface (see p. 19). After close examination they may be distinguished from Bryde's whales by the presence of three ridges along the head (of the Bryde's whale) and by the smaller, more sharply pointed falcate dorsal fin of the Bryde's whale (see Fig. 31). They may be distinguished from sei whales in the following similar ways:

FIN WHALE SEI WHALE

DORSAL FIN

Slightly falcate, forms angle Sharply pointed and falcate: of less than 40 with back forms angle of greater than slightly more than one-third 40 with back well more than forward from tail. one-third forward from tail.

SURFACING BEHAVIOR

Usually rise obliquely so top Primarily skimmer feeders; of head breaks surface first; usually rise to surface at after blowing, animal arches shallow angle so that dorsal its back and rolls forward fin and head are visible exposing the dorsal fin on the almost simultaneously; when long dive; on sounding, the starting the long dive does maximum amount of back in not usually arch the back as the area of the dorsal fin much as the fin whale; on which is exposed is approximately sounding, the maximum 2 times the height of amount of back in the area of dorsal fin. the dorsal fin which is exposed is approximately 1 times the height of the dorsal fin.

BLOW

Tall (to 20 feet [6.1 m]); Similar shape but smaller--rarely inverted cone (point down) taller than 10-15 feet or elongated ellipse. (3.1-4.6 m).

DIVING

Dive for 5-15 (usually 6-7) Dive for 3-10 min; usually min; blow 3-7 times or more blow at even intervals over at intervals of up to several long periods of time; often minutes, then dive again. visible just below the surface, even on longer dives.

COLOR OF UNDERSIDES

White higher up on right Mostly gray; irregular whitish than on left side. area on belly.

COLOR OF LOWER LIP

White on right, gray on left. Gray.

BALEEN PLATES

Right one-fifth to one-third Ash black with a blue tinge in front white; all others and fine grayish bristles.

alternate bands of yellowish white and bluish gray; bristles grayish white.

Distribution

Fin whales are probably the most numerous and widely distributed large whale species in the western North Atlantic.

Fin whales summer from below the lat.i.tude of Cape Cod, Ma.s.s., north to the Arctic Circle. (They are frequently seen between New York and Bermuda this time of year.) Within this zone they may sometimes be seen very close to sh.o.r.e and appear to be concentrated between sh.o.r.e and the 1,000-fathom curve from at least lat. 4120' to 5700' N. In recent years they have been reported in relatively large numbers in the Gulf of Maine from March through June, off Newfoundland as early as June but increasing to August, and entering Davis Straits and beyond in substantial numbers in midsummer to late summer. There is some evidence that the animals venturing farthest north are the largest individuals of the species. Movements of the population(s) southward have usually begun by October, though some fin whales sometimes remain in the northern seas sufficiently long to become trapped in the ice and killed.

During winter the range of fin whales spreads out from the advancing ice southward, reaching at least to the coast of Florida, into the Gulf of Mexico, and to the Greater Antilles, though fin whales are not at all common in tropical waters. During the winter many fin whales move into offsh.o.r.e waters. Northward migrations probably begin in midspring.

Fin whales may be found in Cape Cod waters all year long.

There may be two or possibly three separate stocks of fin whales in the western North Atlantic, one more northern cold-adapted stock and another more southern stock. The ranges of the two stocks appear to overlap, such that the winter range of the northern stock probably becomes the spring and summer range of the more southern stock. The third stock may consist of an isolated population in the northern Gulf of Mexico.

Stranded Specimens

Stranded fin whales may be most readily identified by 1) the yellowish-white coloration of the right front baleen and the right white lower lip; 2) the numerous baleen plates (262-473 in number); 3) the numerous ventral grooves (56-100 in number) extending to the navel and beyond (Table 2); and 4) the broad, flat sharply pointed head with only a single head ridge.