Part 10

Narwhals are found in the high arctic seas of the western North Atlantic, primarily in Lancaster Sound and its fringes. It has been noted that they are found in isolated pockets within that range and are not, like the beluga, widely distributed.

Narwhals make annual migrations in response to the movement of the ice. During the fall as the ice begins to form, the whales migrate to the south, sometimes reaching the Labrador coast. In the spring they return to the pack ice.

May Be Confused With

Narwhals are so different in coloration from the only medium-sized cetacean which shares its range and habitat--the beluga--that the two are highly unlikely to be confused. Belugas are usually all white or light slate gray in color, while narwhals are very much darker, ranging from bluish gray to brownish, and are often covered with light leopardlike spots. Furthermore, the body of the beluga is more robust.

Further, swimming narwhals frequently buck their heads up to breathe, a behavior which makes the tusk of adult males visible and permits positive identification.

Stranded Specimens

Stranded narwhals should be easily identifiable by the distinctive coloration and the unique characteristics of the teeth. In adults, one or two of the teeth may develop into the long, left-hand spiraling tusk, shown in Figures 112 and 114. Immature animals have no teeth which are emerged.

Small Whales, Dolphins, and Porpoises With a Dorsal Fin

ATLANTIC SPOTTED DOLPHIN (T)

_Stenella plagiodon_ (Cope 1866)

Other Common Names

Spotter, Gulf Stream spotted dolphin, spotted porpoise, long-snouted dolphin.[11]

[Footnote 11: See also p. 110. The common name "long-snouted dolphin" was once widely used for this species. It is now more frequently used for _Stenella longirostris_, also known as the spinner dolphin.]

Description

Atlantic spotted dolphins reach a maximum adult length of 7.5, perhaps 8 feet (2.3 to 2.4 m). They are generally more robust in body shape than the other species of Stenella, closely resembling Atlantic bottlenosed dolphins in that regard, though the Atlantic spotted dolphins tend to be more slender.

The dorsal fin is distinctly back-curved and pointed on the tip, also closely resembling that of the Atlantic bottlenosed dolphin.

As the common name suggests, the Atlantic spotted dolphins are marked dorsally with numerous grayish-white spots on a darker background and ventrally with dark spots on a lighter background, though the extent of the spotting and the additional details of coloration change with age.

Immature animals lack spots completely. They are dark gray or purplish gray on the back, becoming lighter gray on the sides and white on the belly. The cape along the back is distinctly separated from the lighter gray coloration of the sides. The flippers and the trailing edge of the flukes are darker than the rest of the body.

As they age, the Atlantic spotted dolphins develop grayish-white spots, first low on the sides, spreading upward. During this stage, the cape becomes less distinct, and dark spotting begins to develop on the belly, the spots increasing in number with increasing age. In adult animals, the belly is often extensively covered with dark blotches but never becomes completely black. The lips may be white, and the beak is characteristically tipped with white, a feature which may aid in identification at sea.

The Atlantic spotted dolphins have a spinal blaze and a light line which extends from the flipper to the eye.

Natural History Notes

Little is known of the natural history of the Atlantic spotted dolphins. The species occurs in herds of up to several hundred individuals, though groups of 50 or fewer (6-10) are more common. They are often seen jumping clear of the water and habitually ride the bow wave of moving vessels. As they do, the distinct cape or band of purplish gray on the back of younger animals and the spotting pattern of older animals may be visible.

Atlantic spotted dolphins feed primarily on squid but may also take carangid fishes, small eels, herring, or anchovies.

May Be confused With

Atlantic spotted dolphins, particularly young animals, may be easily confused with Atlantic bottlenosed dolphins because of the similarities in color pattern and general body shape. However, the Atlantic spotted dolphins have considerable purplish gray in their background colors and the Atlantic bottlenosed dolphins are more dark gray to brownish gray. This along with considerable differences in the overall sizes of the two species should permit positive identification. In general, the key differences between spotted and bottlenosed dolphins are as follows:

ATLANTIC SPOTTED ATLANTIC BOTTLENOSED DOLPHIN DOLPHIN

MAXIMUM SIZE

To 7.5-8 feet (2.3-2.4 m). To 8-10 feet (2.4-3.1 m) inshore, to as much as 12 feet (3.7 m) offshore.

BODY COLOR

Dark purplish gray on back; Dark gray on back; lighter lighter gray on sides and gray on sides; white or pink belly; body becomes on belly (old animals may increasingly spotted with age. have a few spots on belly, but most are not spotted).

HEAD AND BEAK

Head more slender; beak Head robust; beak short; longer; lips and top of snout beak usually uniformly gray often white. (older animals' beak may be white at tip).

NORMAL DISTRIBUTION

Usually found more than 5 Usually more coastal, often miles offshore; most common ascending rivers and entering inside 100-fathom curve. lagoonal and estuarine areas.

Young Atlantic spotted dolphins are so similar in appearance to the Atlantic bottlenosed dolphins that the frequent reports of mixed schools of the two species are probably occasioned by groups of spotted dolphins which include some young, still unspotted animals.

Atlantic spotted dolphins might also be confused with bridled dolphins. The two can be most readily distinguished by the following characteristics:

ATLANTIC SPOTTED DOLPHIN BRIDLED DOLPHIN

BODY SHAPE

Usually robust, often like More slender, more like that of the Atlantic that of the Atlantic striped bottlenosed dolphin. dolphin.

BODY COLOR

Spotted; purplish gray on Spotted; side of head light back; lighter gray on sides gray; body has stripe from and belly becoming flipper to corner of mouth, increasingly spotted with age. though the stripe tends to As animals becomes more fade as spotting increases. spotted, cape become less Cape on top of head more distinct. Body has spinal distinct that on Atlantic blaze and light line from spotted dolphin. Body has no flipper to eye. spinal blaze.

At sea the Atlantic spotted dolphins may also be confused with rough-toothed dolphins (p. 135).

Distribution

Atlantic spotted dolphins are a common species in the continental waters of the tropical and warm temperate western North Atlantic. Although they are far more abundant south of Cape Hatteras, they have been reported from the latitude of Cape May, N.J. (some fishermen claim to have seen them even further north) south through the Gulf of Mexico and the Caribbean to Venezuela. Atlantic spotted dolphins may be replaced around the West Indies by the bridled dolphin.

Within this range, the Atlantic spotted dolphins appear to be generally restricted to the waters outside the 100-fathom curve, most commonly more than 5 miles offshore. However, populations in the Gulf of Mexico move inshore in the late spring, and may approach close to shore during spring and summer.

Stranded Specimens

Stranded Atlantic spotted dolphins may be difficult to distinguish from bridled dolphins. If the color pattern is still clearly visible, the differences in coloration described above, particularly those of the head, and the presence or absence of a spinal blaze may be used. But since external appearance other than coloration are often very similar, specimens should be photographed from as many aspects as possible and the entire specimen or the roughed-out complete skeleton transported to a museum for preparation and examination. Tooth counts recorded for the two species to date are also very similar.

BRIDLED DOLPHIN (T)

_Stenella frontalis_ (G. Cuvier 1829)

Other Common Names

Bridled spotted dolphin, Cuvier's dolphin, gamin (St. Vincent), bridled porpoise.

Description

Bridled dolphins, the second species of spotted dolphins in the western North Atlantic, reach an adult length of at least 7 feet (2.1 m). Like the other, the Atlantic spotted dolphin (p. 104), bridled dolphins are characterized by light grayish-white spots on the dark dorsal portions of the body and dark spots on the light ventral surface. Other details of the coloration differ somewhat. Bridled dolphins are dark gray on the back, fading to lighter gray on the sides and belly. They lack the spinal blaze characteristic of Atlantic spotted dolphins. Except on the head, the border between the back and side colors is indistinct. On the head, the cape (the dark color of the top of the head) is distinct. In the light gray of the side of the head are the markings from which the species derives its common name, "bridled dolphin." These are a black circle around the eye with an extension to the junction (apex) of the rostrum and the melon (present in nearly all dolphins) and a broad black stripe from the origin of the flipper to the corner of the mouth. This mouth-to-flipper stripe tends to fade as spotting increases. Both the upper and lower lips are white or pinkish.

Natural History Notes

Virtually nothing is known of the natural history of bridled dolphins except that they have been observed in small herds of from 5 to 30 individuals and sometimes ride the bow wave of a vessel.

May Be Confused With

At sea, bridled dolphins may be confused with Atlantic spotted dolphins or spinner dolphins. Differences by which they may be distinguished from the first are tabularized on p. 105. Differences between spinner and bridled dolphins permitting identification at sea are as follows:

BRIDLED DOLPHIN SPINNER DOLPHIN

COLORATION

Distinct cape on top of head; Dark gray on back; tan or side of head light gray; yellowish tan on sides; white distinct stripes from flippers on belly, to corner of mouth and from dark circles around eye to apex of melon.

BEAK

Shorter and more slender; all Extremely long and slender; black; lips white. dark gray to black on top, white below; lips black.

DORSAL FIN

Uniformly dark gray. Often lighter gray in middle, dark around border.

Distribution

Bridled dolphins occur in tropical and subtropical waters primarily near coastal areas and islands, but are best known from the West Indies. They have been reported from the Antilles, from Texas, and from Florida north to North Carolina. It has been speculated that this species replaces the Atlantic spotted dolphin around the West Indies.

Bridled dolphins have not yet been described from the South American coast.

Stranded Specimens

Bridled dolphins have from 29 to 34 teeth in each upper jaw and from 33 to 36 in each lower jaw. They can be distinguished from spinner dolphins, which have 46-65 teeth in each jaw, by this character alone.

They may be distinguished from spotted dolphins only if the color pattern of the head is clearly visible. If it has faded, the specimen will probably require museum preparation and examination before it can be positively identified.

SPINNER DOLPHIN (T)

_Stenella longirostris_ Gray 1828

Other Common Names

Long-snouted dolphin, long-beaked porpoise, spinner porpoise, rollover (St. Vincent).

Description

Spinner dolphins reach a maximum length of about 7 feet (2.1 m). The body is slender. The beak varies from extremely long and slender (Fig. 123) to relatively short (Fig. 125); the beak is usually dark on top and clean white below, though there may be some white above. The tip of the snout and the lips are distinctly black, while those of both species of spotted dolphins are light. The back is dark gray to black, the sides are tan to yellowish brown, and the belly is white. Some of the larger animals appear almost all black with faint, light speckling. The dorsal fin is generally moderately falcate, but may be almost triangular in adult males. It is often a lighter gray near the middle, bordered by black or dark gray.

Natural History Notes

Spinner dolphins derive their common name from their habit of leaping clear of the water and spinning on their longitudinal axis. The reasons for this behavior are unknown. Individuals may rotate 2 times, or more, in one leap but spinning behavior is not observed as frequently in the western North Atlantic as it is in the eastern tropical Pacific.

Spinner dolphins occur in herds of up to several hundred individuals and are often seen jumping clear of the water, working the sea surface into a froth. They frequently come to the bow of a boat from considerable distances to ride in the bow wave and may ride for protracted periods.

May Be Confused With

Spinner dolphins may be confused with saddleback dolphins. Both species occur in large herds and often come to moving vessels to ride the bow wave. The two can be distinguished, however, by these differences:

SPINNER DOLPHIN SADDLEBACK DOLPHIN

COLORATION

Dark gray on back; tan or Dark gray to brownish gray yellowish tan on sides; white on back; white on belly with on belly; lacks crisscross crisscross or hourglass pattern pattern on sides; distinct of tan to yellow on sides; black stripe from flipper to distinct black stripe from eye. flipper to middle of lower jaw.

Spinner dolphins might also be confused with bridled dolphins, but may be distinguished by the differences summarized on p. 108.

Distribution

Spinner dolphins are distributed in oceanic and coastal tropical waters. Though one specimen was collected from South Carolina, they have been more frequently reported from both coasts of Florida, the Gulf of Mexico, the Caribbean, and the West Indies. They have also been reported from Venezuela. They are said to be the most abundant dolphin species from the southeastern Caribbean. Some Pacific spinner dolphins are distributed in oceanic zones. Atlantic spinners may be abundant in offshore tropical waters as well.

Stranded Specimens

Stranded spinner dolphins are most readily identified by the extremely long rostrum and the 46-65 teeth, far more than any other species of dolphin. Note that the striped dolphins may have from 43 to 50 teeth per side in each jaw. However, striped dolphins are decidedly larger (to about 9 feet [2.7 m]), have a shorter beak, and are distinctly marked with dark stripes from the eye to the flipper, from the eye to the anus, and from the area behind the dorsal fin forward, towards but not reaching the head.

Saddleback dolphins also have from 40 to 50 teeth on each side but are also easily distinguishable by the differences in coloration discussed above for living animals at sea.

STRIPED DOLPHIN (T)

_Stenella coeruleoalba_ (Meyen 1833)

Other Common Names

Euphrosyne dolphin (_Stenella styx_), Meyen's dolphin, blue-white dolphin, Gray's dolphin, striped porpoise, streaker porpoise.

Description

The striped dolphin is a widely distributed relative of the spinner and the Atlantic spotted dolphins, though it more closely resembles saddleback dolphins than either of these two species. It reaches a maximum length of about 9 feet (2.7 m) and is characterized by a series of distinctive black stripes. One band of black begins near the eye and extends down the side of the body to the area of the anus. (A small secondary stripe originating with this band turns off and disappears in the white coloration of the side just above the flippers.) A second band of black extends from the eye to the flipper. Some workers have contended that striped dolphins are separable into distinct species depending on whether the eye-to-flipper stripe has one (_S. coeruleoalba_) or two (_S. styx_) components.

Most individuals have an additional distinctive finger of black coloration which extends from the black coloration behind the dorsal fin forward towards and about halfway to the eye. It is this feature which is most distinctive in animals riding the bow or leaping clear of the water. The back is dark gray to bluish gray, the sides are lighter gray, and the belly is white.

Natural History Notes

Though little is known of this species, it has been reported in herds of up to several hundred individuals and apparently exhibits behaviors very similar to those of the saddleback dolphins (p. 116), frequently jumping clear of the water. Atlantic and Mediterranean animals have been reported to bow ride.

May Be Confused With

This species is most likely to be confused with the saddleback dolphin, which it closely resembles. The two may be distinguished by the following characteristics:

STRIPED DOLPHIN SADDLEBACK DOLPHIN

LENGTH

To about 9 feet (2.7 m) or Seldom greater than 7.5 feet more. (2.3 m).

COLORATION