Pantropical spotted dolphins (sometimes called "spotters") are slender, streamlined animals. They have a long, slender beak that is separated from the melon by a distinct crease. The dorsal fin is narrow, falcate, and usually pointed at the tip, and the flippers are slender and recurved.
Although unspotted at birth, by adulthood 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 mottling extensive enough to obliterate the cape in coastal dolphins. The lower sides and belly of adults are gray and the lips and beak tip tend to be brilliant white. A dark gray band encircles the eye, and continues forward to the apex of the melon; there also is a dark gape-to-flipper stripe.
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. At birth, pantropical spotted dolphins are about 85 cm long. Adults are from 1.6-2.4 m (females) or 1.6-2.6 m (males). Animals from offshore populations can weigh up to at least 120 kg, but coastal spotted dolphins are larger. In each tooth row are 34-48 slender, sharply pointed teeth.
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 color pattern. Atlantic spotted dolphins can look similar, but attention to head shape, dorsal fin shape, and color pattern details will allow correct identification. In addition to Atlantic spotted dolphins, both bottlenose and humpback dolphins can also be spotted (generally on the belly) but will be distinguishable by differences in body shape and size.
Pantropical spotted dolphins are creatures of oceanic tropical zones, although they do occur close to shore in some areas where deep water approaches the coast. As their name implies, these animals are pantropical, 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.
In the Atlantic Ocean, pantropical spotted dolphins are found in the Gulf of Mexico, Bay of Campeche, the West Indies, along the Atlantic coast of the United States as far north as Cape Hatteras, and east to the Canary Islands.
In the eastern Pacific Ocean, pantropical spotted dolphins are found in the eastern tropical Pacific, in the Gulf of California, and along the coast of Central America and South America to Ecuador and Peru. In the western Pacific, its range includes the coast of Japan and the waters of Micronesia, Indonesia, and the Philippines.
In the Indian Ocean, pantropical spotted dolphins are found in the Bay of Bengal, the waters near India and Sri Lanka, the Gulf of Oman and Gulf of Aden, near the Seychelles Islands, and near Madagascar and the Natal Coast of South Africa.
Ecology and Behavior
These oceanic animals are among the most abundant dolphins in the eastern tropical Pacific (ETP) and are the primary species involved in the tuna/dolphin interaction there. In at least the Pacific and Indian oceans, spotted dolphins associate with yellowfin tuna, spinner dolphins, and other oceanic predators; 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. These gregarious animals are fast swimmers, often engaging in acrobatics, and frequently bowriding (except on the tuna fishing grounds of the ETP, where they generally have learned to avoid boats). Although pantropical spotted dolphins breed year-round, there are two calving peaks in the ETP, one in spring and one in fall.
Feeding and Prey
Pantropical spotted dolphins feed by seizing prey and they have a broad diet, characterized by: Fish>squid>other invertebrates. They feed largely on small epi- and mesopelagic fish, squid, and crustaceans that associate with the deep scattering layer. In some areas, flying fish are also important prey.
The IUCN classifies the pantropical spotted dolphin as “lower risk/conservation dependent”, meaning there are conservation and management programs in place that address the concerns for this species at this time. The United States does not list this dolphin as threatened or endangered.
The greatest known mortality of this species has been in the eastern tropical Pacific (ETP) tuna purse seine fishery for tuna. Since the interaction was first documented in the late 1960s, millions have been killed. Current mortality in this fishery has been greatly reduced by years of modifications to the fishing practices, fleet changes, and United States and international legislation. In addition, pantropical spotted dolphins are taken incidentally in a number of other purse seine, gillnet, and trawl fisheries throughout the range. Large direct kills occur sporadically in the Japanese small cetacean drive and harpoon fisheries, and much smaller direct kills have occurred in the dolphin fisheries of the Caribbean, Sri Lanka, Philippines, Indonesia, St. Helena, and the Laccadive and Solomon Islands.
The United States National Marine Fisheries Service has estimated abundance of several stocks of this species. In 1998, the Pacific population of pantropical spotted dolphins was estimated as follows coastal stock = 108,289 (CV = 0.405), northeast offshore stock = 1,011,104 (CV = 0.264), and western/southern stock = 743,166 (CV = 0.298). The Hawaiian stock was estimated to be 2,928 (CV = 0.45) in 2000. The Gulf of Mexico population was estimated in 1995 to be 31,320 (CV = 0.20). In the Atlantic, NMFS assesses population for pantropical spotted dolphins in conjunction with Atlantic spotted dolphins (S. frontalis) due to difficulties differentiating the two at sea. The best estimate of the combined species in the western North Atlantic, from the Gulf of St. Lawrence to Florida, is 13,117 (CV = 0.56).
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