Part 5

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 offshore 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) assist 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.

BRYDE'S WHALE (B)

_Balaenoptera edeni_ Anderson 1879

Other Common Names

None known.

Description

Bryde's whales reach a maximum length of approximately 46 feet (14 m). They closely resemble sei whales in external appearance. At a distance, the head of this species is similar in profile and general appearance to that of the sei whale. The most distinctive field characteristic of the species, however, is the presence of three ridges along the head anterior to the blowhole. In addition to the medial ridge characteristic of all the other balaenopterid species, Bryde's whales have two secondary ridges on the top of the head--one along each side even with the blowhole running forward towards the tip of the snout. If they can be examined at close range, Bryde's whales can be positively identified by this character alone.

The dorsal fin of Bryde's whales is up to 18 inches (45.7 cm) tall, extremely falcate, pointed on the tip, located well more than one-third forward from the tail, and is often irregularly notched or frayed on the rear margin from unknown causes. Bryde's whales are dark gray overall, though some individuals, like some minke whales, have a small region of gray on each side just forward of the dorsal fin.

Natural History Notes

Bryde's whales, like minke whales, reportedly often approach close to vessels as if curious about them. During this time they may be examined carefully and their identifying characteristics seen.

Though euphausiids may be an important food for this species in limited areas, Bryde's whales often feed on schooling fish (including pilchards, anchovies, herring, and mackerel). This food preference is reflected in the diving behavior of the species. Bryde's whales are not "skimmer" feeders; they are deeper divers. When they surface to breathe, they often rise more steeply to the surface, exposing much of the head, roll the body sharply, and hump up the tail stock before beginning another dive. In this species, as in the fin whale, it can be generally stated that the amount of the back which is exposed above the surface as the animal sounds is approximately twice the height of the dorsal fin. They apparently do not raise the tail flukes when beginning a dive.

May Be Confused With

At sea Bryde's whales may be confused with sei whales, fin whales, and perhaps minke whales.

They may be most readily distinguished from sei whales by the characteristics discussed on p. 32 and by differences in diving behavior. The shallow-feeding sei whales surface and blow at regular intervals over long periods of time. Bryde's whales are deeper divers, less likely to surface, and blow at evenly spaced intervals. If they are seen only briefly or at a distance, however, the two species may be impossible to differentiate.

During the winter months, when fin whales may venture into tropical waters, they may also be confused with Bryde's whales. But fin whales seldom exhibit curiosity about boats. In addition, the dorsal fin of the fin whale is larger, is located farther back on the back than that of Bryde's whale, and does not become visible as soon after the blow. It is also less likely to be worn on the rear margin than that of a Bryde's whale.

The head of the fin whale is more acutely pointed. Furthermore, the right lower lip and the right front baleen of the fin whale are white. The baleen and the right lower lip of Bryde's whales are dark gray. If the animals can be approached closely from the right side, positive identification is possible using these differences in color.

Like Bryde's whales, minke whales often approach close to vessels. But minke whales have an acutely pointed snout, a single head ridge, and a white band on each flipper. Further, minke whales rarely reach 30 feet (9.1 m) in maximum length.

Distribution

The distribution of Bryde's whales is rather poorly known, no doubt in part, because the species is difficult to positively identify at sea, and records of its occurrence may have often been confused with those of sei whales, fin whales, or minke whales. From stranded animals and confirmed sightings at sea, the species appears to be found primarily near shore in areas of high productivity in tropical or subtropical waters, though it ventures into warmer temperate waters as well. It has been reported from Virginia south into the northeast Gulf of Mexico and the southeast Caribbean, and southern West Indies (Curacao and Granada). To date no migration has been described for the species.

Stranded Specimens

Stranded Bryde's whales can be positively identified by the three ridges along the top of the head from the area of the blowhole to the tip of the snout. All other species of balaenopterid whales, except humpback whales have but a single ridge. If the head of a stranded specimen is buried in sand, is decomposed beyond recognition, or is otherwise inaccessible for identification, Bryde's whales can still be distinguished from sei whales by differences in the relative lengths of the ventral grooves (Table 2) and from both the fin whale and the sei whale by differences in the characteristics of the baleen plates (Table 2).

HUMPBACK WHALE (B)

_Megaptera novaeangliae_ (Borowski 1781)

Other Common Names

Humpbacked whale, bunch, hump whale, or hunchbacked whale.

Description

Humpback whales reach a length of 53 feet (16.2 m).

The body is robust, narrowing rapidly on the tail stock. The head is quite broad and rounded, somewhat like that of the blue whale. The head ridge characteristic of other balaenopterid species is indistinct and is replaced in prominence by a string of fleshy "knobs" or protuberances, many more of which are randomly distributed on the top of the head and on the lower jaw. There is a distinctive rounded projection near the tip of the lower jaw. Humpback whales carry many barnacles and whale lice. The baleen plates are all black with black or olive-black bristles.

The flippers are very long (nearly a third as long as the body), are scalloped on at least the leading edge, and are nearly all white.

The dorsal fin, located slightly more than two-thirds of the way back on the back in approximately the same position as that of the fin whale, is small and varies in size and shape from a small, triangular nubbin to a more substantial, sharply falcate fin. The dorsal fin frequently includes a step or hump, which is quite distinct when the animal arches its back to begin a dive and from which the species derives its common name.

Humpback whales are basically black in color with a white region of varying size on the belly, which upon close examination may often be seen to be crosshatched with thin dark lines; the flippers and the undersides of the flukes also are white.

Natural History Notes

The blow of humpback whales is from 8 to 10 feet (2.4 to 3.1 m) tall and has been described as balloon-shaped. It is wide relative to its height. Feeding humpback whales habitually blow 4-8 times at intervals of 15-30 s after a long dive. In the tropics they habitually blow 2-4 times in succession when beginning a long dive. In diving, humpback whales throw the tail flukes high into the air, exposing the sometimes white undersurface and the rippled rear margin.

Humpback whales often leap clear of the water, raise a flipper, and slap it against the water, or "lobtail," raising the tail high into the air and bringing it crashing back to the water in a loud report. Often, particularly when they are encountered on their tropical breeding grounds, humpback whales will be found lying on their sides with a long flipper in the air.

Humpback whales feed on krill and schooling fish.

May Be Confused With

From a distance humpback whales may be confused with any of the other large balaenopterid (rorqual) whales--blue, fin, sei, or Bryde's. Although it is highly variable, the dorsal fin most closely resembles that of the blue whale. However, it is located farther forward on the back. Humpback whales distinguish themselves from the remainder of the rorquals by their habit of raising the flukes high into the air when starting a long dive. (In very shallow water they may not raise the flukes at all.) The only other rorqual to do so--the blue whale--raises the flukes slightly or not at all.

Under some conditions humpback whales may be confused with sperm whales at a distance. When arching the back to begin a dive, both may show a distinct hump. Both species frequently raise their flukes nearly vertically when beginning a long dive but differ in several ways. The flukes of humpback whales show varying amounts of white beneath, are pointed on the tips, and are distinctly concaved and irregularly rippled on the rear margin. Those of sperm whales are all dark and more flattened and even along the rear margin. Further the species can be distinguished in the following ways:

HUMPBACK WHALE SPERM WHALE

BLOW

Projects upwards from center Projects obliquely forward of head. Usually blows from left side of snout. 4-8 times (2-4 times in Usually blows many times tropics) before diving. (20-50 or more) before diving.

HEAD

Raised area around blowholes, Blunted, long, smooth. knobs on upper surface.

FLUKES

Often white underneath, Smooth, all black on rear concaved and scalloped on margin. rear margin, deeply notched.

FLIPPERS

Extremely long (to one-third Short; all black. of body), white and scalloped on leading edge.

DORSAL FIN (OR HUMP)

Triangular to falcate fin, Rounded hump, two-thirds including a step or hump in back on back followed by front of the dorsal fin; knuckles or crenulations. smooth.

When they can be examined at close range, humpback whales can be easily distinguished from all other large whale species with a dorsal fin by the tuberosities or knobs on the head, by the long white flippers scalloped on the leading edge, by the small distinctive dorsal fin, and by their distinctive tail flukes.

Distribution

In the western North Atlantic, humpback whales are widely distributed from north of Iceland, Disko Bay and west of Greenland, south to Venezuela and around the tropical islands of the West Indies. They have been reported from the central and eastern Gulf of Mexico. Summer ranges extend at least from New England north to the pack ice, and feeding concentrations may be found in any portion of this region. During winter, humpback whales migrate southward to the shallow borderlands of Bermuda, to the Bahamas, and to the West Indies to calve and mate.

Stranded Specimens

The most distinctive features of stranded humpback whales are 1) the ventral grooves, 14-22 in number, very wide and extending to the navel; 2) the tuberosities of the snout and lower jaw, often the sites of numerous barnacle colonies; 3) the long flippers (to nearly a third of the total body length); and 4) the distinctive rounded projection near the tip of the lower jaw.

If these characteristics are not sufficiently clear, the species may be identifiable by the characteristics of the baleen plates (Table 2).