Whales, Dolphins, and Porpoises of the Western North Atlantic Part 32

They sometimes move in to ride the bow wave of a vessel, turning on their sides, sometimes spinning completely around on their longitudinal axis when doing so. Individuals may also turn their heads downward or to the side. They are often found close to sh.o.r.e, in bays and lagoons, and sometimes venture up the larger rivers. Some individuals, especially the larger animals, are found as far offsh.o.r.e as the edge of the continental shelf. Atlantic bottlenosed dolphins sometimes ride the surf.

Individuals may jump clear of the water as high as 15-20 feet (4.6-6.1 m), a behavior on which aquarium shows have capitalized.

Members of this species are the dolphins most commonly maintained in captivity at zoos, aquariums, marine parks, and research inst.i.tutions.

For that reason, they are perhaps more familiar to the general public than any other species of porpoise, dolphin, or whale.

May Be Confused With

From at least Cape Hatteras southward, the range of the Atlantic bottlenosed dolphins distributed in insh.o.r.e areas may overlap with that of Atlantic spotted dolphins, particularly during the spring and summer, when the Atlantic spotted dolphins move insh.o.r.e. There the two species may be confused. The Atlantic bottlenosed dolphins and the Atlantic spotted dolphins can be distinguished, however, by the following characteristics:

ATLANTIC ATLANTIC BOTTLENOSED DOLPHIN SPOTTED DOLPHIN

MAXIMUM SIZE

8 feet to as much as 12 feet 7.5-8 feet (2.3-2.4 m).

(2.4 to 3.7 m).

COLORATION

Not spotted (old females may Dark purplish gray on back; have spots on belly); dark lighter gray on sides and gray on back; light gray on belly; body becomes increasingly sides; white or pink on belly. spotted with age.

HEAD AND BEAK

Head robust; beak relatively Head more slender; beak short. longer.

Some Atlantic bottlenosed dolphins are distributed well offsh.o.r.e as far as the edge of the continental shelf. Those individuals may be confused with either rough-toothed dolphins (p. 135) or with grampus (p. 96).

They may be distinguished from rough-toothed dolphins by the following:

ATLANTIC BOTTLENOSED DOLPHIN ROUGH-TOOTHED DOLPHIN

BODY COLOR

Dark gray on back; light Dark gray, almost purplish gray on side; white or pink on with yellow spots; lighter on belly. belly.

SNOUT

Relatively short and stubby, Long and slender; not and clearly demarcated from clearly demarcated from forehead; usually all gray; forehead; lower jaw and lips some older individuals have speckled white.

white-tipped snouts and/or white lips.

Distinguishing differences between the Atlantic bottlenosed dolphins in offsh.o.r.e areas and grampus are tabularized on p. 96.

In northeastern South America the range of the Atlantic bottlenosed dolphin apparently overlaps with that of the Guiana dolphin, which, except for size, it closely resembles (see p. 132).

Distribution

The Atlantic bottlenosed dolphins are widely distributed in the temperate and tropical waters of the western North Atlantic. They are known from at least Nova Scotia but are best known from New England southward to Florida, westward in the Gulf of Mexico, and thence throughout the West Indies and Caribbean to Venezuela.

In the northern portion of that range, Atlantic bottlenosed dolphins are distributed offsh.o.r.e. In the southern portions of their range from at least North Carolina southward, the majority are found nearsh.o.r.e and often enter bays and lagoons, and sometimes venture up the larger rivers. Daily migrations in these areas may follow tidal flow.

In these same southerly areas some Atlantic bottlenosed dolphins are distributed as far offsh.o.r.e as the edge of the continental shelf.

Stranded Specimens

Within their range, stranded Atlantic bottlenosed dolphins should be readily identifiable by 1) the robust body, 2) relatively short beak, and 3) the 20-26 teeth in each upper jaw and 18-24 in each lower jaw.

[Ill.u.s.tration: Figure 142.--Atlantic bottlenosed dolphins leaping on the bow of a research vessel between Cape Cod, Ma.s.s. and Nova Scotia. Note the robust body, the falcate dorsal fin, and the gradation of color in three zones--dark gray on the back, to lighter gray on the sides, to white or pink on the belly. (_Photo by A. Taruski._)]

[Ill.u.s.tration: Figure 143.--A side view of the Atlantic bottlenosed dolphins off St. Augustine, Fla. Note the dark grayish coloration of the back, the lighter coloration of the side, and the tall, sharply angled dorsal fin, pointed on the tip. Though dorsal fin shapes are highly variable, dorsal fins of the Atlantic bottlenosed dolphin are usually more falcate and less pointed on the tip than on these animals. (_Photo courtesy of Marineland of Florida._)]

[Ill.u.s.tration: Figure 144.--Atlantic bottlenosed dolphins frequently ride the bow wave, often turning on their sides as they do so. Note the distinctive color zones, the characteristic shape of the head and beak, and the smooth lines of the flippers. (_Photo by L. Rigley._)]

[Ill.u.s.tration: Figure 145.--An Atlantic bottlenosed dolphin taken at Isla La Blanquilla, off Venezuela. Because they inhabit shallow waters, Atlantic bottlenosed dolphins are infrequent victims of strandings.

(_Photo courtesy of F. Cervigon._)]

[Ill.u.s.tration: Figure 146.--Atlantic bottlenosed dolphins have from 20 to 26 teeth in each side of the upper jaw and from 18 to 24 in each side of the lower jaw. These teeth, sharply pointed in younger animals, may wear substantially as the animal ages. (_Photo courtesy of Wometco Miami Seaquarium._)]

GUIANA DOLPHIN (T)

_Sotalia guianensis_ (P.-J. van Beneden 1864)

Other Common Names

None known.

Description

Guiana dolphins are the second smallest cetacean species in the western North Atlantic, reaching a maximum length of only about 5.6 feet (1.7 m).

Their body shape is very similar to that of the Atlantic bottlenosed dolphin, though the beak is less clearly demarcated from the forehead.

The rather prominent dorsal fin is nearly triangular, curving only slightly backwards near the tip.

Guiana dolphins are steel blue to dark brown on the back and white on the belly. There is sometimes a brownish band extending from the dark color of the back in front of the dorsal fin back towards but not reaching the a.n.u.s.

Natural History Notes

Guiana dolphins are usually found in groups of fewer than 10 individuals.

May Be Confused With