Whales, Dolphins, and Porpoises of the Western North Atlantic Part 11

[Ill.u.s.tration: Figure 15.--The heads of fin whales surfacing to breathe off j.a.pan and in the northern North Atlantic (inset). When they can be approached from the right side, fin whales can be positively distinguished from the other large balaenopterine species by the white coloration of the right lower lip and the flat, narrow head. Note also the single central head ridge. (_Photos by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura, and K. C. Balcomb_ (_inset_).)]

[Ill.u.s.tration: Figure 16.--A small group of fin whales off British Columbia. Fin whales may be found in groups of up to six or seven individuals and these groups may congregate in feeding grounds. (_Photo by G. C. Pike, courtesy of I. MacAskie._)]

[Ill.u.s.tration: Figure 17.--The back of a harpooned fin whale in the eastern North Pacific (left) and in the North Atlantic (right). In both note the light grayish-white chevrons just behind the head. These chevrons are not usually very distinctive in North Atlantic fin whales.

In the animal in the left photo note also the prominent ridge along the back behind the dorsal fin--a characteristic which prompted the common name "razorback." (_Photos courtesy of_ Los Angeles Examiner (_left_) _and K. C. Balcomb_ (_right_).)]

[Ill.u.s.tration: Figure 18.--Surfacing fin whales show the head and blow, then the wheellike silhouette of the back, and then the dorsal fin. Note that in this species the dorsal fin is smaller and located farther back than that of the sei whale and appears on the surface later after the animal's blow. (_Photo from the northern North Atlantic by K. C.

Balcomb._)]

[Ill.u.s.tration: Figure 19.--As they begin a long dive, fin whales frequently arch the tail stock high into the air, exposing the dorsal fin. Even on a long dive, however, this species is not known to throw its tail flukes high into the air or even to raise them slightly, as blue whales sometimes do when beginning a long dive. (_Photo from off Virginia by J. G. Mead._)]

[Ill.u.s.tration: Figure 20.--Probably a fin whale (perhaps a Bryde's whale) breaching in the eastern tropical Pacific. This type of behavior has been described for humpback, minke, and fin whales but is far more common for the first two species. Breaching fin whales often reenter the water with a resounding splash, much like humpback whales, but sometimes smoothly, head first, as minkes sometimes do. (_Photo by K. D. s.e.xton, courtesy of National Marine Fisheries Service._)]

[Ill.u.s.tration: Figure 21.--A head-on view of a fin whale stranded at Ormond Beach, Fla. Note the flat narrow appearance of the head and the single, central head ridge. (_Photo by F. Essapian, courtesy of Marineland of Florida._)]

[Ill.u.s.tration: Figure 22.--In this partly flensed fin whale, at Blanford, Nova Scotia, note the white lower lip and the white baleen in the right front. The inset photo shows the right upper jaw of a fin whale with the baleen intact. (_Photos by H. E. Winn, and from the North Pacific by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura (inset)._)]

[Ill.u.s.tration: Figure 23.--A fin whale on the ramp of the whaling station also at Blanford, Nova Scotia. Note the ventral grooves, 56 to 100 and extending at least to the navel. (_Photo by L. Rigley._)]

SEI WHALE (B)

_Balaenoptera borealis_ Lesson 1828

Other Common Names

Pollack whale, sardine whale, Rudolphi's rorqual.

Description

Sei (p.r.o.nounced "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

The blow of sei whales is an inverted cone rarely taller than 15 feet (4.6 m).

Sei whales are generally skimmer feeders and do not usually dive very deeply. For that reason they usually surface at a shallower angle than fin whales. The head rarely emerges at a steep angle (except when the whales are chased). Instead, the blowholes and a major portion of the back, including the dorsal fin, become visible almost simultaneously and remain visible for relatively long periods of time. In this species it can be generally stated that the amount of the back in the area of the dorsal fin which is exposed above the surface as the animal sounds is approximately the same height as the dorsal fin. When they begin another dive, sei whales do not arch the tail stock or flukes high. Instead, they normally submerge by slipping quietly below the surface, often remaining in view only a few feet down and leaving a series of tracks or swirls on the surface as they move their tail flukes. When they are feeding in this manner, sei whales may exhibit a highly regular blowing and diving pattern over long periods of time.

Sei whales usually travel in groups of from two to five individuals, though they may concentrate in large numbers on the feeding grounds.

In the northern portion of their range, sei whales feed on copepods.

Throughout the remainder of the range, however, their food is more varied and also includes krill and a variety of small schooling fishes.

The species derived its common name, in fact, from its frequent occurrence with or near sei fish.

May Be Confused With

The sei whale's smaller size and decidedly taller, more falcate dorsal fin located well more than one-third forward from the tail should prevent confusion with the blue whale. At a distance, however, sei whales are difficult to distinguish from either fin whales or Bryde's whales. The primary clues for distinguishing them from fins are the differences in swimming, blowing, and diving characteristics tabularized in detail on p. 26 and the asymmetrical coloration of the fin whale.

Sei whales may be distinguished from Bryde's whales only upon close examination. The dorsal fin of Bryde's whales is small, to 18 inches (45.7 cm), sharply pointed, and often worn on the rear margin. If close examination is possible, the sei whale will be seen to have only a single head ridge. Bryde's whales have two additional ridges--one on each side of the main ridge. Bryde's whales are primarily fish feeders and their diving behavior more closely resembles that of a fin whale than that of a sei whale. (See p. 37).

Distribution

The distribution and migrations of the sei whale during most of the year are rather poorly known. The species is known to avoid the colder regions near the pack ice and to range from Iceland south to the northeast Venezuelan coast and the northeast and southwest Gulf of Mexico. There are also records from Cuba and the Virgin Islands. Along the northeast United States and eastern Canadian coasts, where most research on sei whales has been conducted, the species migrates from New England through the Blanford, Nova Scotia area in June and July, is found in small numbers off eastern Newfoundland in August and September (abundant in Placentia Bay, Newfoundland in August), and continues northward to the Davis Straits in September and October. An offsh.o.r.e stock may be found year-round in the Labrador Sea. The summer range (May to September or October) extends from New England to southern Arctic waters. Though some individuals remain behind through November, the southward movement of the bulk of the population presumably begins in October. In general, sei whales do not venture as far north as fin whales but may have a greater tendency to enter tropical waters.

Stranded Specimens

Stranded sei whales are most likely to be confused with fin whales or Bryde's whales. The three head ridges of the Bryde's whale (sei whales have only one) a.s.sist in distinguishing sei whales from Bryde's whales.

They may be distinguished from fin whales and all other rorquals by the following characteristics: 1) The color of the baleen plates--uniformly ash black with a blue tinge and fine white bristles (Table 2). 2) The density of bristles on the plates--sei whales have from 35 to 60 baleen fringes per centimeter; all other rorquals have far fewer (less than 35). 3) The relative lengths of the ventral grooves--the grooves of sei whales end well before the navel; those of blue, fin, and Bryde's whales extend at least to the navel. 4) The relatively small numbers of ventral grooves (38-56)--both blue and fin whales have more; Bryde's whales have approximately the same number.

If the animal is not in an advanced state of decomposition, the region of white coloration of the belly may also be visible.

[Ill.u.s.tration: Figure 24.--The head of a sei whale is intermediate in shape between that of the blue whale and that of the fin whale. When viewed from the side it is slightly arched. Note the single central head ridge, from just in front of the blowholes to near the tip of the snout.

Bryde's whales, with which sei whales are most likely to be confused in the tropical and subtropical portions of their range, have two auxiliary ridges, one on each side of the top of the head, in addition to this main central ridge. (_Photo from the North Pacific by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura._)]

[Ill.u.s.tration: Figure 25.--Sei whales are dark gray on the right lower lip. They can be distinguished from fin whales, which have a white right lower lip, by approaching them from the right side. (_Photo from the North Pacific by j.a.panese Whales Research Inst.i.tute, courtesy of H.

Omura._)]

[Ill.u.s.tration: Figure 26.--Three views of swimming sei whales. In all three, note the tall, distinctly falcate dorsal fin (which has been described as sickle or scimitar in shape) positioned farther forward on the back than the fins of either the fin whale or the blue whale. In the photo in the middle, note that the dorsal fin has appeared on the surface while the blowholes are still open. Sei whales, generally skimmer feeders and rather shallow divers, often show the dorsal fin and much of the back for relatively long periods as they surface to breathe.

(_Photos from off central California, courtesy of National Marine Fisheries Service_ (_middle_); _northeast of Hawaii by S. Ohsumi_ (_left inset_); and _from off j.a.pan by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura_ (right inset).)]

[Ill.u.s.tration: Figure 27.--A freshly dead sei whale from the Pacific (top) and a stranded specimen in an advanced stage of decomposition at Cape Island, S.C. (bottom and inset). Note that even though the distinctive coloration of the fresh specimen has faded on the rotting specimen, the numbers and lengths of the ventral grooves (38 to 56 in number and stopping well short of the navel) still permit the specimen to be distinguished from fin, blue, and Bryde's whales, in all of which the grooves extend at least to the navel. (_Photos by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura (top); and J. G. Mead (bottom and inset)._)]

[Ill.u.s.tration: Figure 28.--Dorsal view of a sei whale on the deck of a whaling ship in the North Pacific. Note the numerous scars on the body and the otherwise dark gray coloration of the back. (_Photo by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura._)]

[Ill.u.s.tration: Figure 29.--The right upper jaw of the sei whale stranded at Cape Island, S.C. The baleen plates, here partly buried in the sand, numbering from 318 to 340 per side and uniform dark gray with fine lighter gray bristles, continue to serve as identifying characteristics even on a badly decomposed specimen. (_Photo by J. G. Mead._)]

BRYDE'S WHALE (B)

_Balaenoptera edeni_ Anderson 1879

Other Common Names

None known.