Part 4

In this species it can be generally stated that the maximum height of back in the area of the dorsal fin which is exposed above the surface as the animal sounds is approximately four times the height of the dorsal fin itself. The exposure of the tail flukes is unlike that of the humpback whale (Fig. 39), the right whale (Fig. 50), or the sperm whale (Fig. 57) in that when beginning a long dive all these other species raise the flukes high out of the water and usually descend at a steep angle. Blue whales lift the flukes only slightly, if at all.

Blue whales are relatively shallow feeders, feeding as they do almost exclusively on "krill" (small shrimplike crustaceans), most of which are distributed in the surface 330 feet (100 m). Blue whales usually occur singly or in pairs.

May Be Confused With

At sea, blue whales may be confused with fin whales (p. 26) and though the two are sometimes difficult to distinguish from a distance, the following key differences permit identification at close range:

BLUE WHALE FIN WHALE

COLORATION

Mottled bluish gray above Gray above, white below; frequently and below. grayish-white chevron behind head, right lower lip white.

BALEEN

All black. Bluish gray with yellowish-white strips; front fifth to third of baleen on right side all white.

HEAD

Broad and nearly U-shaped; Narrower, more V-shaped; all dark. right lower lip white.

DORSAL FIN

To 13 inches (33 cm); triangular To 24 inches (61 cm); falcate; to moderately falcate; in located slightly more than a last third of back; visible well third forward from tail after blow. flukes; usually visible shortly after blow.

SURFACING AND PREPARING TO DIVE

Often shows head and blowholes; Usually rolls higher out of broad expanse of back water, particularly on long and much later, dorsal fin. dive; dorsal fin visible shortly after blow.

DIVING

Dives for 10-20 min; surfaces Dives 5-15 min (most often and blows 8-15 times, making 6-7); surfaces steeply for 3-7 a series of 12- to 15-s dives blows then dives rather between blows, then disappears steeply again; does not show again; sometimes raises flukes on dive: on sounding, flukes slightly on last dive; the maximum height of back on sounding, the maximum in the area of dorsal fin which height of back in the area of is exposed is approximately 2 dorsal fin which is exposed is times the height of the dorsal approximately 4 times the fin. height of the dorsal fin.

GROUPING

Usually found singly or in Occasionally found singly or pairs. in pairs, more often found in pods of six or seven individuals; many pods, consisting of as many as 50 animals, may be found in small area.

See also comparison of fin whale and sei whale (p. 26).

Distribution

Though blue whales have been reported from the pack ice to Cristobal Harbor, Panama Canal Zone, their normal range in the western North Atlantic is more limited. In spring and summer months (about April through at least August) they can be expected in the northern portion of their range, at least as far north as the Arctic Circle, feeding on the krill abundant in those waters. A small portion of the population may venture north, beyond the Circle. In fall and winter the population moves south, presumably into temperate and perhaps to tropical waters. Reliable records include animals from observations off Long Island and Ocean City, Md.

Though southern limits of the species are poorly known, there are no records from Florida or the West Indies and no verified records from the Gulf of Mexico.

Summaries of blue whale distribution based on records when the species was more numerous indicate that they were found during spring and summer months in some abundance on the Nova Scotian Banks, the St. Lawrence Gulf and estuary, the Strait of Belle Isle, Grand Bank, and in the waters off the coasts of Iceland, southern Greenland, and the Davis Straits and Baffin Bay. (Some individuals have entered the Hudson Strait but not apparently Hudson Bay itself.)

Historically, a few animals apparently appeared off the coast of southeastern Canada as early as February. It was speculated that from there a portion of the population underwent a migration from the Strait of Belle Isle north through the Davis Straits to the waters off western Greenland. Some individuals entered the Gulf of St. Lawrence after the ice was clear and remained behind until as late as November. In the fall months, certainly by November, the northern portion of the population had begun retreating to the south in front of the advancing ice. The remainder apparently also underwent this migration as well, since blue whales have historically been nearly absent from Canadian waters during midwinter.

Many of the migrating individuals were assumed to continue south to temperate and, less frequently, to tropical water where they calved. It should be emphasized that though all of the southward and the subsequent northward migrations were presumed to be along pelagic routes, details were poorly documented.

Blue whales have been reported in both shallow inshore and deep oceanic zones.

Despite considerable attention in the popular literature to the plight of the blue whale populations and frequent statements that they are near extinction, blue whale stocks in the western North Atlantic appear more abundant than has been usually reported. While present stocks are far short of previous population sizes, which may have exceeded 200,000 individuals worldwide, they should be sufficiently large for the species to continue their increase, barring renewed exploitation.

Stranded Specimens

Stranded blue whales can be readily identified by 1) the large body size (to 85 feet [25.9 m]); 2) the broad flat head; 3) the all-black baleen plates (270-395 in number), which are usually barely more than twice as long as they are wide; and 4) the 55-88 ventral grooves extending to the navel or beyond (Table 2).

Depending on the state of decay and the position of the stranded specimen, any of the body characteristics described for living animals may also be used to positively identify the specimen.

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 deg. 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 constitute 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 deg. with back forms angle of greater than slightly more than one-third 40 deg. 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 latitude of Cape Cod, Mass., 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 shore and appear to be concentrated between shore and the 1,000-fathom curve from at least lat. 41 deg.20' to 57 deg.00' 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 offshore 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.

SEI WHALE (B)

_Balaenoptera borealis_ Lesson 1828

Other Common Names

Pollack whale, sardine whale, Rudolphi's rorqual.

Description

Sei (pronounced "say") whales have been reported to reach 62 feet (19 m).

The snout is less acutely pointed than that of the fin whale but when viewed from the side appears slightly arched. In general, the head is intermediate in shape between that of the blue whale and that of the fin whale. The dorsal fin, which is from 10 to 24 inches (25.4 to 61 cm) tall and strongly falcate in adult animals, is located about two-thirds of the way back on the back, farther forward than that of the blue or fin whales. Sei whales are dark steel gray on the back and sides, and on the posterior portion of the ventral surface. The body often has a galvanized appearance due to scars possibly resulting from lamprey bites inflicted during migrations into warmer waters. These scars may be dark gray to almost white in color. On the belly there is a region of grayish white that is confined to the area of the ventral grooves. Neither the flippers nor the tail flukes are white underneath. The right lower lip and the mouth cavity, unlike those of the fin whale, are uniformly gray. The baleen plates are uniformly grayish black with fine grayish-white fringes. (A small number of sei whales have been noted to have a few half-white plates near the front of the mouth, a feature which might result in their confusion with fin whales.)

Natural History Notes