Whales, Dolphins, and Porpoises of the Western North Atlantic Part 12

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 s.p.a.ced 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 sh.o.r.e 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).

[Ill.u.s.tration: Figure 30.--On the head of this Bryde's whale off La Jolla, Calif. two of the three head ridges characteristic of the species, the main ridge and the left auxiliary ridge, are clearly visible. These ridges permit this animal to be positively identified as a Bryde's whale. (_Photo by F. Morejohn._)]

[Ill.u.s.tration: Figure 31.--Bryde's whales in the Gulf of California and north of Hawaii (inset). In both, note the tall, sickle-shaped appearance of the dorsal fin, much like that of the sei whale. In the animal in the larger photo note the ragged rear margin of the dorsal fin, a frequently observed characteristic in Bryde's whales. In the animal on the left note also the region of gray on the sides in front of the dorsal fin. (_Photos by W. C. c.u.mmings and S. Ohsumi_ (_inset_).)]

[Ill.u.s.tration: Figure 32.--Stranded Bryde's whales at Walnut Point, Va.

(top) and Panacea, Fla., Gulf of Mexico (bottom). In both animals note the head shape similar to that of the sei whale, and the three distinct head ridges. In the animal on the bottom, note that the two outermost ridges have their origin in grooves beside the blowholes. In the animal on the top, note also the baleen plates, up to at least 300 per side and dark gray with coa.r.s.e gray bristles. There is infrequently a rather wide interval at the front of the mouth between the left and right rows of baleen. (_Photos by U.S. National Museum, courtesy of J. G. Mead (top) and M. B. Rank, courtesy of Wide World Photos (bottom)._)]

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 "k.n.o.bs" 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 cras.h.i.+ng 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.