Whales, Dolphins, and Porpoises of the Western North Atlantic Part 29

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; hourgla.s.s 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 a.n.u.s, 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 splas.h.i.+ng. 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 hourgla.s.s 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 Ma.s.sachusetts, 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 s.h.i.+ft 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).

[Ill.u.s.tration: Figure 130.--Saddleback dolphins captured off St.

Augustine, Fla., shown in the tank at Marineland of Florida. The highly distinctive crisscross or hourgla.s.s pattern of tan or yellowish tan on the sides is clearly visible. Note also the light tip of the snout and the dark line from the center of the lower jaw to the flipper. This last characteristic readily distinguishes the saddleback dolphin from the striped dolphin, in which the black stripe begins at the corner of the mouth rather than near the center of the lower jaw. (_Photos courtesy of Marineland of Florida._)]

[Ill.u.s.tration: Figure 131.--Saddleback dolphins on the bow of a s.h.i.+p off Ma.s.sachusetts in 1966. The color pattern, including the dark brownish-gray back, the crisscross pattern on the sides, and the white belly, are clearly visible. The light tip of the snout helps distinguish this species from the spinner dolphins, which have a black-tipped snout.

(_Photo by E. Wheeler._)]

[Ill.u.s.tration: Figure 132.--The distinctive crisscross pattern of the sides of the saddleback dolphins is clearly visible even when comparatively little of the animal is seen. Note the falcate dorsal fin, which often, as here, is dark on the border, lighter near the center.

(_Photo by R. K. Brigham, courtesy of National Marine Fisheries Service._)]

[Ill.u.s.tration: Figure 134.--A saddleback dolphin stranded on Westerly Beach, R.I. The origin of the common name "crisscross dolphin" is evident in the color pattern of the side. Note also the distinctive black stripe from the center of the lower jaw to the origin of the flipper. (_Photo courtesy of H. E. Winn._)]

[Ill.u.s.tration: Figure 133.--Saddleback dolphins frequently jump clear of the water and may reenter in a variety of ways: 1) smoothly, head first; 2) with a chin slap; 3) with an accompanying tail lob; or 4) on the sides or back with a splash. This habit enables them to be spotted from a considerable distance. When stressed, herds bunch tightly together, like the group in the bottom photo. (_Photos from off Virginia by J. G.

Mead (top) and off San Diego, Calif. by S. Leatherwood (bottom)._)]

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 p.r.o.nounced dark stripe, similar to that found on the striped dolphin, extending from the rostrum to the area of the a.n.u.s. 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 a.n.u.s. Just below and parallel to this cream-white band is a black one extending from the area of the eye to the a.n.u.s. 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 a.n.u.s; area of a.n.u.s. 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.