Part 12

ATLANTIC BOTTLENOSED DOLPHIN (T)

_Tursiops truncatus_ (Montague 1821)

Other Common Names

Bottlenosed porpoise, gray porpoise, common porpoise.[12]

[Footnote 12: See also p. 150 for use of this common name for another species, the harbor porpoise.]

Description

Atlantic bottlenosed dolphins reach a maximum overall length of about 12 feet (3.7 m) and weigh in excess of 1,430 pounds (650 kg). They have relatively stubby snouts and dorsal fins, which are broad at the base, tall, and falcate. Coloration varies slightly, but individuals are usually dark gray on the back, lighter gray on the side, grading to white or pink on the belly. Old females may have spots on the belly. The dark coloration of the back often appears as a highly distinct cape, particularly on the head.

Natural History Notes

Atlantic bottlenosed dolphins often occur in groups of up to several hundred individuals which usually consist of aggregations of small groups of no more than a dozen animals each. They frequently associate with the Atlantic pilot whales and are frequently found accompanying the right and humpback whales travelling along the Atlantic coast of Florida.

Atlantic bottlenosed dolphins have catholic tastes, feeding on shrimp, eels, catfish, menhadden mullet, and miscellaneous trash fish, to mention only a few. They are frequently found near shrimp boats, feeding on fish stirred up by the trawls or on discarded trash fish.

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 shore, in bays and lagoons, and sometimes venture up the larger rivers. Some individuals, especially the larger animals, are found as far offshore 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 institutions. 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 inshore areas may overlap with that of Atlantic spotted dolphins, particularly during the spring and summer, when the Atlantic spotted dolphins move inshore. 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 offshore 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 offshore 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 offshore. In the southern portions of their range from at least North Carolina southward, the majority are found nearshore 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 offshore 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.

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 anus.

Natural History Notes

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

May Be Confused With

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 nearshore extend into only very and in bays, river mouths, shallow nearshore waters on and estuaries, but extend limited area of South American farther offshore. coast.

Distribution

Guiana dolphins are found in Lake Maracaibo, in the rivers of Guyana, and in the nearshore 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 distinguishing 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.

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 offshore 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 assumed 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 distinguishing 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.)

PYGMY KILLER WHALE (T)

_Feresa attenuata_ Gray 1874

Other Common Names

Slender blackfish, slender pilot whale.

Description

Pygmy killer whales reach a length of about 8-9 feet (2.4-2.7 m). They are usually relatively slender-bodied with a rounded head, an underslung jaw, and no beak.

The falcate dorsal fin, located about the center of the back, is usually between 8 and 12 inches (20.3 and 30.1 cm) tall (though it may reach 15 inches [38 cm] in some individuals), is sometimes very distinctive, and resembles that of the Atlantic bottlenosed dolphin. The flippers are slightly rounded on the tips.

The color has been described as dark gray or black on the back, often lighter on the sides, extending higher in front of the dorsal fin and with a small zone of white on the underside, often a lighter gray area on the sides, and distinctive white regions around the lips. The chin may be completely white. This white zone on the chin, described as a "goatee," is often clearly visible in swimming animals.

May Be Confused With

The pygmy killer whale resembles the false killer whale but is much smaller and can be distinguished at close range by the zones of white coloration. False killer whales are almost all black and reach a length of up to at least 18 feet (5.5 m). Pygmy killer whales are dark gray on the back, often lighter on the sides, and show a region of white on the belly which may extend so high up onto the sides that it is visible on a swimming animal. Further, they reach only 8-9 feet (2.4-2.7 m).

Pygmy killer whales may also be confused with the similarly sized and colored many-toothed blackfish. So little is known of the two species' appearance and behavior at sea that it is doubtful that they can be successfully distinguished, though many-toothed blackfish apparently lack the white region often seen on the sides of pygmy killer whales. Further, pygmy killer whales have rounded flippers and smoothly tapered heads, while those of the many-toothed blackfish are pointed on the tip and more sharply pointed (often described as a parrot beak).

Distribution

Pygmy killer whales are probably distributed in the tropical and subtropical waters of the western North Atlantic. They have been reported from Texas, the Atlantic coast of Florida, and St. Vincent Island, Lesser Antilles. Records of the species from the other oceans of the world suggest that its distribution is limited to tropical and subtropical waters.

Stranded Specimens

Stranded pygmy killer whales can be clearly distinguished from both the false killer whale and the many-toothed blackfish. In addition to the differences discussed above, the following are key differences between the pygmy and false killer whales:

PYGMY KILLER WHALE FALSE KILLER WHALE

TEETH

10-13 in each side of upper 8-11 per jaw per side, and lower jaws; lower teeth prominent. smaller.

VENTRAL COLORATION

White from anus to under tail Dark from anus to tail stock; stock, white may extend up lighter pale gray area forward sides. between flippers.

FLIPPERS

Smoothly rounded. Characteristic hump on forward margin.

Pygmy killer whales can be distinguished from many-toothed blackfish on the basis of the second species' larger number of teeth. (Many-toothed blackfish have from 22 to 25 teeth in the upper jaw and from 21 to 24 in the lower jaw.)

MANY-TOOTHED BLACKFISH (T)

_Peponocephala electra_ (Gray 1846)

Other Common Names

Hawaiian blackfish, melon-headed whale.

Description

Many-toothed blackfish reach lengths of at least 9 feet (2.7 m) and are similar in body shape to the larger false killer whale and the similar-sized pygmy killer whale. The body is elongated and slim with a rather slim tail stock. In general, the head is shaped like that of the false killer whale but has a sharper appearance to the snout, sometimes described as a parrot-beak. The forehead is rounded, slightly overhanging the lower jaw, and has no beak. The dorsal fin is up to 10 inches (25.4 cm). It is probably very distinctive as the animals surface to breathe. Many-toothed blackfish are black on the back and slightly lighter on the belly. The areas around the anus and genitals and the lips are unpigmented. Many-toothed blackfish are presumably rare.

May Be Confused With

Many-toothed blackfish may be confused with either the false killer whale or the pygmy killer whale. They are considerably smaller than the false killer whale, have a slightly more pointed snout, and lack the prominent humplike forward margin on the flippers which is characteristic of the false killer whale.

They are approximately the same size as pygmy killer whales, but the white area around the genitals which extends up onto the side in pygmy killer whales may be lacking in many-toothed blackfish. This species has pointed flippers, while those of pygmy killer whales are rounded on the tips. Many-toothed blackfish also have a slightly more pointed snout. Otherwise, the two species are virtually indistinguishable in encounters at sea.

Distribution

Although many-toothed blackfish have not yet been reported in the western North Atlantic, they are included in this guide because of a record from the eastern tropical North Atlantic and the known tropical distribution in other areas.

Stranded Specimens

Stranded many-toothed blackfish can be distinguished from false killer and pygmy killer whales by the number of teeth alone. Many-toothed blackfish have more than 15 per side per jaw (usually 21-25); both other species have less than 15.

PYGMY SPERM WHALE (T)

_Kogia breviceps_ (Blainville 1838)