Whales, Dolphins, and Porpoises of the Western North Atlantic Part 28

[Ill.u.s.tration: Figure 126.--A spinner dolphin harpooned in the fishery at St. Vincent, Lesser Antilles. Even after subtle aspects of the color pattern have faded, this species can be readily identified by the 46-65 teeth in both upper and lower jaws and by the distinctly black lips and black-tipped rostrum. (_Photo by W. A. Huck, courtesy of Marineland of Florida._)]

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 a.n.u.s. (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

Back from light gray to dark Back basically black or gray to bluish gray; sides brownish; distinct white gray; belly gray or white; chest or belly patch; distinctive black lateral hourgla.s.s or crisscross stripping from 1) eye to pattern on the sides; flipper, 2) eye to a.n.u.s, and 3) distinct black stripe from dark color behind dorsal fin flipper to middle of lower forward, towards but not jaw.

reaching head.

Distribution

Striped dolphins are widely distributed in the temperate, subtropical, and tropical seas of the western North Atlantic. They have been reported from at least Halifax, Nova Scotia, south as far as Jamaica. (Additional records, purportedly from southern Greenland, involved a museum specimen. Since striped dolphins of the eastern North Atlantic are rare north of England, the species occurrence near Greenland would be highly improbable.) Individuals have recently been reported from the Gulf of Mexico.

Despite this wide distribution, striped dolphins appear to prefer warmer waters and are probably normally confined to the Gulf Stream or the waters off the continental slope. Individuals appearing to the north of the range seem to have ventured northward with fingers of warm water.

Stranded Specimens

Stranded striped dolphins should be readily identifiable by the highly distinctive patterns of lateral striping discussed above for living animals. If the color pattern has faded, they may still be identified by their size, larger than other dolphin species of similar appearance, and the relatively large number of teeth (43-50 per side in both upper and lower jaws). Only the spinner dolphin, much smaller in body length and having a much longer beak, has more teeth (46-65 per side in each jaw).

[Ill.u.s.tration: Figure 127.--Despite some similarities in appearance and behavior to saddleback dolphins, striped dolphins can be readily identified by the prominent dark stripes on the side of the body. These striped dolphins were photographed between the Caribbean Islands of Curacao and Bonaire in 1972. (_Photo by D. Poppe._)]

[Ill.u.s.tration: Figure 128.--When they ride the bow, the most apparent characteristic of striped dolphins is usually the dark streak beginning in the black coloration behind the dorsal fin and extending forward towards but not reaching the head. This stripe is not always present, however, and the species may sometimes appear uniformly pale gray from a distance. (_Photo from the tropical Atlantic by H. E. Winn._)]

[Ill.u.s.tration: Figure 129.--Stranded striped dolphins. Note the distinctive black stripes 1) eye to flipper, 2) eye to a.n.u.s, and 3) (on top animal) from black behind dorsal fin forward towards but not reaching the head. Some workers contend that striped dolphins are separable into two species, depending on whether the eye-to-flipper stripe has one (_Stenella coeruleoalba_) or two (_S. styx_) components.

Others contend that the two belong to the same species (_S.

coeruleoalba_). Striped dolphins have from 43 to 50 teeth in each upper and lower jaw. (_Photos from j.a.pan by W. E. Schevill (top) and from Indian Rocks Beach, Fla. by W. A. Huck, courtesy of Marineland of Florida (bottom)._)]

SADDLEBACK DOLPHIN (T)

_Delphinus delphis_ Linnaeus 1758

Other Common Names

Saddleback porpoise, common dolphin, crisscross dolphin.

Description

Saddleback dolphins reach a maximum overall length of about 8.5 feet (2.6 m) though most individuals are less than 7.5 feet (2.3 m) long.

Males are slightly larger than females of the same age.

The body shape varies slightly but usually closely resembles that of the striped dolphin (p. 113). The dorsal fin varies from nearly triangular to distinctly falcate and is pointed on the tip. It is sometimes all black and sometimes black on the borders with a lighter grayish region of varying size near the middle.

The back is basically black or brownish black, but this coloration and the extent of the striping patterns that form the impression of a saddle and the degree of color distinction between the different zones are highly variable.

The chest and belly are cream white to white and are the most distinctive features from a distance. Up close, the sides will be seen to be distinctly marked with an hourgla.s.s or crisscross pattern of tan or yellowish tan. This crisscross pattern is diagnostic for the species.

The rostrum is intermediate in length and shape between that of the spinner and that of the striped dolphin and is often black with a white tip.

Natural History Notes

Saddleback dolphins are often seen in herds of a thousand or more and are often very active, many animals leaping clear of the water at any time. Like spinner dolphins, saddleback dolphins are active bow-riders and often come to the boat from considerable distances. Once on the bow they often ride for extended periods of time.

Saddleback dolphins feed on squid and on a variety of fishes, including anchovies, myctophids, and hake.

May Be Confused With

Saddleback dolphins might easily be confused with striped dolphins and must be examined closely to be distinguished from them. Primary differences apparent in encounters at sea are as follows: