Whales, Dolphins, and Porpoises of the Western North Atlantic Part 33

Because of their limited range and specialized habitats, Guiana dolphins are unlikely to be confused with any other cetacean species except perhaps Atlantic bottlenosed dolphins (p. 128). These two species can be distinguished by the following characteristics:

GUIANA DOLPHINS ATLANTIC BOTTLENOSED DOLPHINS

SIZE

To only 5.6 feet (1.7 m). 8 to as much as 12 feet (2.4 to 3.7 m).

DORSAL FIN

More nearly triangular; curved Broad-based, tall, and only slightly backwards falcate.

near tip.

DISTRIBUTION

Found in rivers and estuaries, Sometimes found nearsh.o.r.e extend into only very and in bays, river mouths, shallow nearsh.o.r.e waters on and estuaries, but extend limited area of South American farther offsh.o.r.e.

coast.

Distribution

Guiana dolphins are found in Lake Maracaibo, in the rivers of Guyana, and in the nearsh.o.r.e coastal waters of the northeastern portion of the Guianas.

Stranded Specimens

In their very limited range, stranded Guiana dolphins can be readily identified by their extremely small size (to 5.6 feet [1.7 m]) and nearly triangular dorsal fin. Furthermore, in addition to the characteristics listed above distinguis.h.i.+ng living Guiana dolphins from Atlantic bottlenosed dolphins, the species can be distinguished by differences in the numbers of teeth:

ATLANTIC BOTTLENOSED GUIANA DOLPHINS DOLPHINS

TEETH

20-26 in each upper jaw; 26-35 in each jaw; often 18-26 in each lower jaw. ragged in arrangement.

[Ill.u.s.tration: Figure 147.--A Guiana dolphin from Kartabo, British Guiana. In the coastal portion of its range along the northeastern South American coast, this species is most likely to be confused with the Atlantic bottlenosed dolphin. Guiana dolphins are much smaller, rarely exceeding 5.6 feet (1.7 m), have a more triangular dorsal fin, and tend to be found more frequently in estuaries and rivers. (_Photo by A. B.

Van Beneden from Zoologica VII(4), by permission of the New York Zoological Society._)]

[Ill.u.s.tration]

[Ill.u.s.tration: Figure 148.--Guiana dolphins harpooned in Kartabo, British Guiana. Guiana dolphins have from 26 to 35 teeth in each jaw.

Atlantic bottlenosed dolphins, which are larger but somewhat similar in appearance, have from 20 to 26 teeth in each upper jaw and from 18 to 26 in each lower jaw. (_Photo by A. B. Van Beneden from Zoologica VII (4), by permission of the New York Zoological Society._)]

ROUGH-TOOTHED DOLPHIN (T)

_Steno bredanensis_ (G. Cuvier in Lesson 1828)

Other Common Names

Rough-toothed porpoise, goggle-eyed porpoise.

Description

Rough-toothed dolphins reach a length of at least 8 feet (2.4 m). The coloration of the rough-toothed dolphins is quite variable. Individuals are often dark gray to dark purplish gray on the back with pinkish-white blotches on the sides and belly. The flippers and flukes are dark and the belly is white. Individuals are frequently scarred with numerous white streaks.

The most distinctive characteristic of the rough-toothed dolphin is its beak, which is quite long and slender, may be white or pinkish white along both sides, including one or both lips and the tip of the snout, and is not separated from the forehead by the transverse groove present in other long-snouted dolphins. Because the forehead and the sides of the head slope smoothly into the rostrum, when this animal is seen from above or from the side, its entire head appears very long and nearly conical.

Natural History Notes

Rough-toothed dolphins occur in small groups of 50 animals or fewer and are usually found off the edge of the continental slope. They may ride the bow waves.

May Be Confused With

In their offsh.o.r.e habitat, rough-toothed dolphins are most likely to be confused with Atlantic spotted dolphins (p. 104) and with Atlantic bottlenosed dolphins (p. 128). They may be distinguished from Atlantic spotted dolphins by the following:

ROUGH-TOOTHED DOLPHIN ATLANTIC SPOTTED DOLPHIN

SNOUTS

Long and slender; not clearly Moderate in length and demarcated from forehead. clearly demarcated from forehead.

They may be distinguished from Atlantic bottlenosed dolphins by the characteristics tabularized on p. 128.

Even at a distance the blotched coloration of the side and the white coloration of the rostrum of rough-toothed dolphins may be visible. If closer examination is possible, the distinctive shape and coloration of the beak make positive identification easy.

Distribution

Though records of rough-toothed dolphins from the western North Atlantic are scant, the species is a.s.sumed to be widely distributed in deep tropical to warm temperate waters. It has been reported from Virginia, Georgia, Florida, the Gulf of Mexico, the West Indies, and off the northeastern coast of South America.

Stranded Specimens

In addition to the characteristics listed above for distinguis.h.i.+ng living animals, stranded rough-toothed dolphins can be readily identified by the fact that the 20-27 fairly large teeth per jaw per side have a series of fine vertical wrinkles on the crown, a characteristic from which the species derives its common name. (These wrinkles are often difficult to detect.)

[Ill.u.s.tration: Figure 149.--Captive rough-toothed dolphins in j.a.pan.

Note the distinctive, smoothly tapering head and the white coloration of the sides and front of the snout. Rough-toothed dolphins are probably widely distributed in the offsh.o.r.e waters of the tropics. The streamers on the backs of the animals are marker tags (see Appendix A.) (_Photo courtesy of j.a.panese Whales Research Inst.i.tute._)]

[Ill.u.s.tration: Figure 150.--Closeups of the highly distinctive head of a rough-toothed dolphin showing the white lips and the lack of a clear demarcation between the snout and the forehead. This species has from 20 to 27 fairly large teeth in each side of both the upper and lower jaws.

(_Photos at Sea Life Park, Hawaii, by K. C. Balcomb (top) and S.

Leatherwood (bottom)._)]