Part 11

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 hourglass or crisscross stripping from 1) eye to pattern on the sides; flipper, 2) eye to anus, 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).

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 hourglass 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:

SADDLEBACK DOLPHIN STRIPED DOLPHIN

COLORATION

Back basically black or Back from light gray to dark brownish; distinct white gray to bluish gray; sides chest or belly patch; hourglass gray; belly gray or white; or crisscross pattern on distinctive black lateral sides, some tan to yellowish striping from 1) eye to tan; distinct black stripe flipper, 2) eye to anus, and from flipper to middle of 3) dark color behind dorsal lower jaw. fin forward, towards but not reaching head.

LENGTH

To 7.5 feet, rarely to 8.5 feet To 9 feet (2.7 m). (2.3-2.6 m).

From a distance, saddleback dolphins might also be confused with spinner dolphins because of the habits of both species of congregating in large schools with much jumping and splashing. Both species ride the bow wave, and close examination should permit positive identification using the following characteristics:

SADDLEBACK DOLPHIN SPINNER DOLPHIN

COLORATION

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

Distribution

Saddleback dolphins are widely distributed in the temperate, subtropical, and tropical waters of the western North Atlantic Ocean. They have been reported off Newfoundland, Iceland, Nova Scotia, and the coast of Massachusetts, south along the coast of North America to the Caribbean (West Indies and Jamaica), in the Gulf of Mexico, and from South American waters at least to Margarita Island, Venezuela.

The species' occurrence in the more northerly portions of this range during the summer and early fall months appears to coincide with the intrusion of warm waters into those areas. They are not uncommon off Nova Scotia in summer and fall and are casual members of the marine mammalian fauna of the remaining Maritime Provinces during that period.

In previous years, saddleback dolphins were not uncommonly encountered by collectors of Marineland of Florida working the northeast coast of Florida, but the species has been conspicuously absent since about 1960. Reasons for this apparent shift of range are unknown.

Stranded Specimens

Saddleback dolphins have from 40 to 50 small, sharply pointed teeth in each side of both the upper and lower jaws. These numbers overlap with only those of the striped and spinner dolphins (with 43-50 and 46-65, respectively). Saddleback dolphins should be readily distinguishable from both these species by the features outlined under the descriptions of living animals and distinguishable from the bridled dolphins by the distinctive markings on the head of the two species (see Figs. 121 and 134).

FRASER'S DOLPHIN (T)

_Lagenodelphis hosei_ Fraser 1956

Other Common Names

Sarawak dolphin, Bornean dolphin, Fraser's porpoise.

Description

Fraser's dolphins reach an overall length of at least 8 feet (2.4 m). They are extremely short-beaked and have a pronounced dark stripe, similar to that found on the striped dolphin, extending from the rostrum to the area of the anus. They are robust in build and have rather small flippers and dorsal fin relative to body size. The dorsal fin is slender, falcate, and pointed on the tip. The body is gray on the back and white on the belly. The color of the side is dominated by the striping pattern. A cream-white band beginning high on the rostrum extends above and past the eye, continues towards the tail, and finally dissipates in the body color above the anus. Just below and parallel to this cream-white band is a black one extending from the area of the eye to the anus. A second cream-white band below and parallel to this dark strip separates the darker gray coloration of the side from the white coloration of the belly. The flippers are dark above and below.

Natural History Notes

The little that is known of the natural history and behavior of the species may be summarized as follows: Fraser's dolphins occur in groups of up to at least 500 animals and in the Pacific are occasionally seen with spotted dolphins (_Stenella attenuata_). From all accounts, they are not uncommon in certain areas of the tropical Pacific and off South Africa.

Fraser's dolphins appear to be deep divers. They are aggressive swimmers and, when they surface to breathe, often charge to the surface, creating a spray from their heads. They have also been reported leaping clear of the water.

May Be Confused With

Fraser's dolphin is intermediate in form between _Lagenorhynchus_ and _Delphinus delphis_ (thus the composite name _Lagenodelphis_). Because the species is apparently limited to tropical waters, however, and because of the prominent stripe on the side of the body, Fraser's dolphins are more likely to be confused with the striped dolphins (p. 113). The two species can be distinguished at sea by several characteristics:

FRASER'S DOLPHIN STRIPED DOLPHIN

COLORATION

Single broad black stripe Color dominated by series of from beak and eye back to stripes from: 1) eye to anus; area of anus. 2) eye to flipper, and 3) black behind dorsal fin forward, towards but not reaching the head.

BEAK

Extremely short and indistinct. Longer, much more distinctive.

BODY SHAPE

Robust, particularly in front Slenderer. of dorsal fin.

FLIPPERS

Small, dark in color, and Longer, sometimes lighter originating in light color of on upper surface; note stripe sides. from front of flippers to eye.

DORSAL FIN

Small, slender, slightly Taller dorsal fin, broader at falcate, and pointed on top. base.

Distribution

Although Fraser's dolphins have yet to be described for the western North Atlantic Ocean, they are included here as "possibles" because of the recent discovery that their range is far more extensive than previously known. Records to date have been limited to offshore tropical waters.

The species was first described in 1956 from the remains of a beach-washed specimen from Sarawak in the South China Sea. Since that time specimens have been collected from the eastern tropical Pacific, and others have stranded in such widely divergent localities as Australia, South Africa, and Japan. Recent summaries have added sighting records from the Central Pacific, near the Phoenix Island, from northwest of the Galapagos Islands, and from South African waters.

Stranded Specimens

Stranded Fraser's dolphins should be readily identifiable by 1) distinctive coloration of the body; 2) short, indistinctive beak; and 3) robust form. The only other species of small dolphins with beaks of similar length and general appearance are the Atlantic white-sided and white-beaked dolphins (p. 123 and 126); these dolphins, both with far more northerly ranges, have 30-40 and 22-28 teeth in each side of each jaw, respectively, while Fraser's dolphins have from 40 to 44 teeth in the upper jaw and from 39 to 44 in the lower jaw.

ATLANTIC WHITE-SIDED DOLPHIN (T)

_Lagenorhynchus acutus_ (Gray 1828)

Other Common Names

Atlantic white-sided porpoise, jumper (Newfoundland).

Description

Atlantic white-sided dolphins reach about 9 feet (2.7 m) in maximum length and are robust in form with a small but distinct beak (less than 2 inches [5.1 cm] long).

The dorsal fin is tall, distinctly back curved, and pointed on the tip. The tail stock is extremely thick and does not narrow laterally until very near the tail flukes.

The back is distinctly black, the belly white. The sides have zones of gray, tan, and white.

The single most distinctive feature of Atlantic white-sided dolphins is an elongated oval zone of white and yellowish white along the sides from just below the dorsal fin to the area above the anus. These patches of lighter coloration, clearly demarcated from each other and from the surrounding coloration, are frequently visible simultaneously with the dorsal fin as the animals roll at the surface to breathe. Even alone this feature permits positive identification of the species. The dorsal fin is often part gray, part black. The beak is all black.

Natural History Notes

Atlantic white-sided dolphins are known to congregate in herds of perhaps a thousand animals, though smaller herds are far more common. The species is often wary of ships and does not ordinarily ride the bow wave. Like a number of other species, white-sided dolphins have been reported in association with Atlantic pilot whales.

May Be Confused With

At sea, Atlantic white-sided dolphins are most likely to be confused with the white-beaked dolphins, with which they overlap in distribution. Though they are very similar in general appearance, the two can be distinguished in the following ways:

ATLANTIC WHITE-SIDED DOLPHIN WHITE-BEAKED DOLPHIN

COLORATION

Elongated band of yellowish Two grayish areas--one in white and white along side, front, the other below and visible behind and below behind dorsal fin, visible as dorsal fin as animal rolls. animal rolls.

BEAK

All black. Sometimes white in parts of range though western Atlantic animals are usually dark.

MAXIMUM SIZE

To 9 feet (2.7 m). To 10 feet (3.1 m).

DORSAL FIN

Often part black, part lighter Uniformly dark. gray.

Distribution

Atlantic white-sided dolphins are distributed, primarily offshore, in the cool waters between the Gulf Stream and the Labrador Current. They have been observed from Hudson Canyon, off New York City, north to southern Greenland and perhaps Davis Straits. Their normal range shares a southern boundary with the white-beaked dolphin but does not extend as far to the north.

Stranded Specimens

In addition to the features described above for living animals at sea, stranded Atlantic white-sided dolphins can be distinguished from white-beaked dolphins by the following:

ATLANTIC WHITE-SIDED DOLPHIN WHITE-BEAKED DOLPHIN

NUMBER OF TEETH

30-40 per side per jaw, 22-28 per side per jaw; have sometimes more in upper. larger individual teeth--to 6 mm in diameter.

FLIPPERS

Lower portion of forward Lower portion of forward margin more curved. margin less acutely curved.

VENTRAL COLOR

White coloration of belly White coloration of belly extends high onto sides of extends to lower jaw but not body. above flippers on sides.

CAUDAL CRESTS

Tail stock strongly compressed Tail stock less laterally laterally; taller, narrows compressed, tapers more rapidly just in front of flukes. gently towards tail flukes.

WHITE-BEAKED DOLPHIN (T)

_Lagenorhynchus albirostris_ Gray 1846

Other Common Names

White-beaked porpoise, squidhound (Newfoundland).

Description

White-beaked dolphins reach a maximum overall length of about 10 feet (3.1 m). The body is robust in form with a tall, uniformly dark-gray dorsal fin, and a short but distinct beak which, as the common name implies, is often light gray to white above and below, at least in European waters. The beak of animals in the western Atlantic populations is less frequently white. The back and sides are basically dark gray to black, and the belly is white to light gray.

Swimming white-beaked dolphins can be most readily identified by the two areas of pale coloration on the sides, one in front of and another below and behind the dorsal fin. These areas are clearly visible from a ship or aircraft as the animals roll at the surface.

Natural History Notes

White-beaked dolphins may sometimes occur in herds of up to 1,500 individuals. Like their cousins, the Atlantic white-sided dolphins, they do not commonly ride the bow waves of vessels.

White-beaked dolphins feed on squid, octopus, cod, herring, capelin, and sometimes on benthic crustaceans.

May Be Confused With

In their northerly range white-beaked dolphins are likely to be confused with only the Atlantic white-sided dolphins. The most distinctive features of white-beaked dolphins are 1) the two areas of paleness described above, 2) the prominent, dark gray dorsal fin, and sometimes 3) the white beak. Other features by which the two species may be distinguished in the brief encounters typical at sea are tabularized on p. 127.

Distribution

White-beaked dolphins are the more northerly of the two species of _Lagenorhynchus_ in the western North Atlantic. They are found from Cape Cod, Mass., north to western and southern Greenland and Davis Straits, though they are apparently far more numerous to the north of this range. They appear in Davis Straits in spring and summer and leave that area in autumn, sometimes as late as November, to move southward. They winter as far south as Cape Cod, where they are the common dolphin species in April, May, and June (sometimes to July). Their migrations are poorly known.

Stranded Specimens

Stranded white-beaked dolphins can be most readily distinguished from white-sided dolphins by the substantial differences in coloration and the differences in numbers of teeth.

ATLANTIC WHITE-SIDED WHITE-BEAKED DOLPHIN DOLPHIN

TEETH

22-28 per side per jaw. 30-40 per side per jaw, sometimes more in upper jaw.

COLORATION

Beak sometimes gray or Beak all black; side marked white above and below; two with elongated areas of pale areas visible on living white with streaking patterns animals not visible on stranded of yellow and tan. specimens.

Additional characteristics by which the two species may be distinguished are summarized on p. 123.