(Gray, 1846) - Pantropical spotted dolphin
Distinctive Characteristics
Pantropical spotted dolphins (sometimes called “spotters”) are generally slender, streamlined animals. They have a long thin beak that is separated from the melon by a distinct crease. The dorsal fin is narrow, falcate, and usually pointed at the tip.
Although unspotted at birth, by adulthood Pantropical spotted dolphins have varying degrees of white mottling on the dark dorsal cape, which is narrow on the head and sweeps low on the flank in front of the dorsal fin. The spotting ranges from very slight (or even non-existent) in offshore animals to heavy enough to obliterate the cape in coastal dolphins. The lower sides and belly of adults are grey and the lips and beak tip tend to be brilliant white. A dark grey band encircles the eye, and continues forward to the apex of the melon; there also is a dark gape-to-flipper stripe.
In each tooth row are 34 to 48 slender, sharply pointed teeth.
In at least the eastern tropical Pacific, a separate coastal form exists. It is larger and stockier, with a thicker beak and more extensive spotting than the offshore form.
Coastal and offshore form description
Coastal spotted dolphin (Coastal form of Stenella attenuata): Body and beak relatively robust; heavy spotting that nearly obliterates cape; known distribution limited to within 185 km of the coast in the eastern tropical Pacific.
Offshore spotted dolphin (Offshore form of Stenella attenuata): Body and beak slender; spotting slight to moderate; maximum body length 2.3 m; distributed more than 30 km from shore in eastern tropical Pacific and found in oceanic waters worldwide.
Can be confused with
Pantropical spotted dolphins can be confused with several other long-beaked oceanic dolphins. Spinner dolphins can be distinguished by differences in dorsal-fin shape, beak length, and colour pattern. In addition to Atlantic spotted dolphins, both bottlenose and hump-backed dolphins can also be spotted (generally on the belly), but will often be distinguishable by differences in body shape and size.
Size
Adults are from 1.6 to 2.4 m (females) or 1.6 to 2.6 m (males). Animals from offshore populations can weigh up to at least 120 kg, but are smaller than those from coastal ones. At birth, pantropical spotted dolphins are about 85 cm long.
Geographical Distribution
Pantropical spotted dolphins are mostly creatures of oceanic tropical zones. As their name implies, these animals are found in all oceans, between about 40°N and 40°S, although they are much more abundant in the lower latitude portions of their range.
Biology and Behaviour
These animals are among the most abundant dolphins in the eastern tropical Pacific and are the primary species involved in interactions with tuna there. Pantropical spotted dolphins associate with yellowfin tuna, spinner dolphins, and other pelagic predators; the fishermen take advantage of this association to help them locate and catch tuna more efficiently.
School sizes are generally less than 100 for the coastal form, but offshore herds may number in the thousands. In the eastern tropical Pacific, large herds are less common than they were before the tuna fishery began to exploit them. These gregarious animals are fast swimmers, often engaging in acrobatics, and frequently bowriding (except on the tuna fishing grounds of the eastern tropical Pacific, where they generally have learned to avoid boats).
There are 2 calving peaks in the eastern tropical Pacific, 1 in spring and 1 in autumn.
Pantropical spotted dolphins feed largely on epipelagic fish and squid, primarily during the day.
Exploitation
The tuna fishery in the eastern tropical Pacific targets the pantropical spotted dolphin to catch yellowfin and skipjack tuna that often swim below the herds. Annual mortality of spotted dolphins in the late 1980s was in the tens of thousands. Takes of hundreds of thousands per year in the 1960s and 1970s reduced the northern offshore stock of spotters to an unknown degree. Spotted dolphins are also taken in other fisheries, including drive fisheries in Japan and the Solomon Islands, and Sri Lankan gillnet and harpoon fisheries for human consumption, among others. Some have been reported taken in the Caribbean small cetacean fishery.
IUCN Status
Insufficiently known.