Whales, Dolphins, and Porpoises of the Western North Atlantic Part 18

The fact that goosebeaked whales strand more frequently than other beaked whales may reflect either a greater abundance or a greater tendency to approach close to sh.o.r.e.

They are probably primarily an offsh.o.r.e species.

Stranded Specimens

To be positively identified, stranded goosebeaked whales in an advanced state of decomposition may require museum preparation and examination of the skull and teeth. Fresh specimens may be tentatively identified by the characters ill.u.s.trated in the figures.

[Ill.u.s.tration: Figure 71.--Goosebeaked whales have been rarely seen at sea. In these photos from the eastern tropical Pacific, note the white head of the animal on the left. Goosebeaked whales are wary of boats and may dive for 30 min or more. When they surface, their blow, usually very indistinct, may project forward and slightly to the left. (_Photos by K.

D. s.e.xton, courtesy of National Marine Fisheries Service._)]

[Ill.u.s.tration: Figure 72.--A beaked whale, probably a goosebeaked whale, jumps beside a research ship off northwestern Baja California. Note the position and shape of the dorsal fin and the depression just behind the head. (_Photo by S. Leatherwood._)]

[Ill.u.s.tration: Figure 73.--A goosebeaked whale stranded in Delaware.

Goosebeaked whales are primarily tropical in distribution, though they apparently venture into temperate areas in summer. Note the prominent dorsal fin, the lighter coloration of the head, and the depression just behind the head. (_Photo from U.S. National Museum, courtesy of J. G.

Mead._)]

[Ill.u.s.tration: Figure 74.--A closeup of the dorsal surface of the flukes of a juvenile goosebeaked whale stranded in the northeastern Gulf of Mexico. Like other members of the beaked whale family, goosebeaked whales lack a distinctive notch in the rear margin of the flukes.

(_Photo courtesy of Florida's Gulfarium._)]

[Ill.u.s.tration: Figure 75.--Stranded goosebeaked whales, an adult male from northern California (top) and an immature female from the northeastern Gulf of Mexico (bottom). Note the brownish color of the back, marked in the adult animal by blotches of lighter gray and numerous scratch marks, presumably tooth rakes. Note also the mouth cleft, shorter in this species than in any other beaked whale species, and the slightly concave appearance to the upper margin of the head. The beak is usually less developed in large animals. The inset photo shows a ventral view of the tip of the lower jaw of an adult male from the east coast of Florida. The two teeth of the species are emerged above the gum only in adult males. (_Photos by W. J. Houck (top), Florida's Gulfarium (middle), and W. A. Huck, courtesy of Marineland of Florida (inset)._)]

OTHER BEAKED WHALES (T)

_Mesoplodon_ spp.

Other Common Names

Grampus (St. Vincent) (see also p. 96).

Description

In addition to the northern bottlenosed whale (p. 67) and the goosebeaked whale (p. 70), four other species of beaked whales have been reported from the western North Atlantic. All four species are known primarily from stranded specimens and have been rarely encountered at sea. Therefore statements of range are usually limited to inferences from locations of strandings, and information on appearance and habits of the species in the wild is almost totally lacking.

The infrequent encounters with beaked whales at sea may result from such factors as 1) a low inconspicuous blow, 2) avoidance of ships, and/or 3) distribution in small groups in offsh.o.r.e areas well outside the normal boating lanes.

The following descriptions will aid primarily in identifying stranded specimens. Though subtle differences in ranges, color patterns, and dorsal fin shapes and positions may be helpful in narrowing the choices of living animals, the species will continue to be extremely difficult to distinguish from one another in the brief encounters typical at sea until additional data are collected.

The beaked whales have the following characteristics in common: 1) two small creases forming a V-shape on the throat, 2) the absence of a conspicuous notch on the rear margin of the tail flukes (some specimens have a slight indentation), and 3) the absence of functional teeth in all except adult males. Adult males have a single pair of teeth in the lower jaw, the position and description of which help to identify the species. The teeth of females are not functional and only rarely emerge from the gums. Therefore, if a stranded animal is an adult male, its species can be determined by the position and description of the teeth.

For example, in _Mesoplodon mirus_, the teeth are located near the tip of the lower jaw; in _M. europaeus_, they are located about a third of the way from the tip of the snout to the corner of the mouth; in _M.

bidens_, they are nearly half way from the tip of the snout to corner of the mouth; and in M. densirostris, they are located in large prominences near the back of the mouth.

If the animal is a female or an immature male, however, museum preparation and examination might be required before the species can be positively determined. The following four sections summarize characters of western North Atlantic beaked whales.

[Ill.u.s.tration: Figure 76.--An unidentified beaked whale from the mid-Pacific. Note the marks along the back, presumably tooth rakes, consisting of scratches that are paired and close together. A beaked whale in the western North Atlantic marked in this manner would be a northern bottlenosed whale (p. 67), a goosebeaked whale (p. 70), or a True's beaked whale (p. 77). These are the only three species in which the teeth are located close together near the tip of the lower jaw.

(_Photo by K. C. Balcomb._)]

[Ill.u.s.tration: Figure 77.--Various views of a herd of five or six unidentified beaked whales, possibly dense-beaked whales, 12 miles off Pokai Bay, Oahu, Hawaii. The animals were very shy and had low indistinct blows, making them difficult to spot and track. As they surfaced, individuals frequently bucked their heads and slapped the chin against the surface, rather than rolling. They did not raise their tail flukes when beginning their long dives. (_Photos by E. Shallenberger, Sea Life Park, Hawaii._)

(Because so little is known of beaked whales every encounter should be recorded in as much detail as possible.)]

[Ill.u.s.tration: Figure 78.--Adult male beaked whales, showing the body profile and the relative positions of the teeth. Remember that the teeth of females and immature males are concealed beneath the gums. (_Drawing by L. Winn._)]

TRUE'S BEAKED WHALE (T)

_Mesoplodon minis_ True 1913

Other Common Names

None known.

Description

True's beaked whales reach a length of at least 16 feet (4.9 m) long.

They are chunky in midbody and narrow rapidly towards the tail, closely resembling goosebeaked whales (p. 70). In overall body shape, the head is small with a slight indentation in the area of the blowhole, a slight bulge to the forehead, and a p.r.o.nounced beak. The flippers are small (from one-fourteenth to one-tenth the body length). The dorsal fin is small, slightly falcate, located in the latter third of the back, and followed by a p.r.o.nounced ridge on the tail stock. The flukes, which sometimes contain a very slight notch, are broad (to almost one-fifth the body length).

True's beaked whales are dull black to dark gray on the back, lighter slate gray on the sides, and white on the belly. The body is frequently covered with light colored spots or splotches and bears numerous pairs of scratch marks, presumably tooth rakes (Fig. 76).

The flippers are all black and are attached in the dark coloration of the animal's side. The flukes are dark above and below.

May Be Confused With

True's beaked whales are most likely to be confused with goosebeaked whales (p. 70) but may also be confused with any of the other beaked whales species (p. 74 and Fig. 78).

Distribution

True's beaked whales appear to be primarily temperate in distribution.

They have been reported from Cape Breton Island, Nova Scotia south as far as Flagler Beach in Florida. Northernmost records are for summer months.

The range of True's beaked whales overlaps with that of the Antillean beaked whale but is more northerly.

Stranded Specimens

The teeth of adult male True's beaked whales may be visible near the tip of the lower jaw, a characteristic shared with the goosebeaked whale (p.

70) and the northern bottlenosed whale (p. 67). Both these other species reach substantially greater maximum lengths than True's beaked whales, however, and should be readily distinguishable by this and the number of other highly distinctive characteristics of each species.