Whales, Dolphins, and Porpoises of the Western North Atlantic Part 9

Blue whales are the largest living mammals. Though reports of maximum length and weight vary from one account to another, Antarctic blue whales are known to have reached lengths to 100 feet (30.5 m) and weights of over 150 tons (136,363 kg)[10] before stocks were severely depleted by whaling operations. North Atlantic blue whales may be expected to reach lengths of 80-85 feet (24.4-25.9 m). In all known populations of blue whales, females are slightly larger than males of the same age.

[Footnote 10: The largest measured specimen was "just over" 100 feet (30.5 m); the largest specimen weighed, the 150-ton individual noted above, was 89 feet (27.1 m) long.]

Viewed from above, the blue whale's rostrum is broad, flat, and nearly U-shaped (actually shaped like a Gothic arch, slightly flattened on the tip), with a single ridge extending from the raised area just in front of the blowholes towards but not quite reaching the tip of the snout.

The dorsal fin is extremely small [to only 13 inches (33 cm)] and variable in shape from nearly triangular to moderately falcate. In all cases, it is located so far back on the animal's tail stock that it is seldom visible until the animal is about to begin a dive.

Blue whales are light bluish gray overall, mottled with gray or grayish white. Some animals may have yellowish or mustard coloration, primarily on the belly, the result of the acc.u.mulation of diatoms during long stays in the cooler waters to the north. The undersides of the flippers are light grayish blue to white.

The baleen plates are all black.

Natural History Notes

The blow or "spout" is tall, to perhaps 30 feet (9.1 m), slender, vertical, and not bushy, as is the blow of humpback whales, for instance.

Although the blowing and diving patterns of blue whales may vary, depending on the speed of movement and the activity of the whale when it is encountered, they may be generally described as follows: If the animal is moving slowly, the blowhole and part of the head may still be visible when the dorsal fin breaks the surface, and the animal may settle quietly into the water without exposing the last portion of the tail stock or the tail flukes. If the animal is moving more quickly, however, or is about to begin a long dive, the blowhole disappears below the surface, a broad expanse of the back is exposed and disappears, and the dorsal fin emerges briefly just before the animal lifts its tail stock and flukes slightly above the surface before slipping out of sight.

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 Ca.n.a.l 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 a.s.sumed 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 doc.u.mented.

Blue whales have been reported in both shallow insh.o.r.e 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.

[Ill.u.s.tration: Figure 9.--Closeup views of swimming blue whales off British Columbia (top) and Baja California (bottom). In both photos note the broad rounded appearance of the head and the single, prominent central head ridge. In the animal on the top note also the black baleen plates, barely visible at the front of the slightly open mouth. In the animal on the bottom note the pattern of light grayish-white mottling along the back and the raised areas around the blowholes. These features clearly mark these animals as blue whales. (_Photos by R. M. Gilmore (top) and K. C. Balcomb (bottom)._)]

[Ill.u.s.tration: Figure 10.--The dorsal fins of blue whales may vary from distinctly triangular (top) to broadly rounded (middle and inset) to smoothly falcate in appearance (bottom). Regardless of its shape, however, the fin is always located well back on the tail and does not become visible until long after the animal's blow. (_Photos by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura, mid-Pacific (top); S.

Leatherwood, southern California (middle and inset); and F. W. True, northern North Atlantic, courtesy of U.S. National Museum (bottom)._)]

[Ill.u.s.tration: Figure 11.--A blue whale swimming leisurely at the surface off San Clemente Island, Calif. Note that the blowholes, marked by the raised areas on the top of the head, are still exposed after the dorsal fin has become visible. Note also the very small size and the shape of the dorsal fin and its position well back towards the tail.

(_Photo by S. Leatherwood._)]

[Ill.u.s.tration: Figure 12.--A sequence showing fast-swimming blue whales off southern California. The animal rises rather steeply to the surface (a), emits a tall, vertical blow (b, c), shows its broad bluish back, mottled with grayish white, and its small dorsal fin (d, e), and then dives out of sight (f). When swimming in this manner, blue whales sometimes raise their tail flukes slightly above the surface before beginning their long dives (g). (_Photos by J. F. Fish (a-f) and K. C.

Balcomb (g)._)]

[Ill.u.s.tration: Figure 13.--Two views of blue whales on the ramps of whaling stations in j.a.pan (top) and at Hermitage Bay, Newfoundland (bottom). Note the broad rounded appearance of the head, the single central head ridge, and the dark bluish-gray coloration, interrupted only by mottlings of grayish white. In the animal on the bottom note the all-black baleen plates, which are very broad relative to their length.

(_Photos by j.a.panese Whales Research Inst.i.tute, courtesy of H. Omura (top); and F. W. True, courtesy of U.S. National Museum (bottom)._)]