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Spotted Dolphin

Human Threats:Due to the yet unexplained association between large yellowfin tuna and some dolphin stocks in the ETP, the coastal spotted and other dolphins have been the target of the tuna purse-seine fishery that uses the dolphins' locations to find tuna. The coastal spotted dolphin is considered to be one of the dolphin species most affected by this fishery, but the extent to which this mortality has affected the population is unknown. During the early years of the purse seine fishery, fishing effort was concentrated near the coast. Therefore, coastal dolphin stocks such as this one may have experienced high mortality. Because this species only occurs near the coast, they are infrequently seen on research vessel surveys, and data often used to estimate abundance of other dolphin stocks are not available, such as relative abundance, absolute abundance, and time-series of mortality.


COLOR:Color varies according to geographical location, age, and the individual. Generally speaking, these animals go through five color phases:newborn calves are dark gray with a white belly and no spots.The color changes to two-tone, sharply divided, dark on top, light on belly and no spots;
adolescent phase when dark spots begin to appear on the lower part of the body;
light spots appear on the dark upper portion of the body;
dark ventral (underside) spots merge almost into a solid color with pink shading on the forward part of the belly.Its beak is black and the lips and tip of the beak are white. A dark link extends from the middle of the lower jaw to the flipper and both eyes are circled in black with a black connecting line from each eye across the beak.

Biology:All dolphins of the genus Stenella or "stenellids" are relatively small dolphins when compared to other dolphins, such as the bottlenose dolphin (Tursiops truncatus), and coastal spotted dolphins are reach lengths of approximately 6 ft. - 7 ft., weighing approximately 250 lbs. at adulthood. They have long, slender snouts or beaks. Mating and calving occurs year-round, with gestation being that of most dolphins, around eleven months. Like the Atlantic spotted dolphin (Stenella frontalis), pan-tropical spotted dolphins are without spots when born, accumulating them as they age until they are almost completely covered with overlapping patterns. Pan-tropical spotted dolphins are also distinguished by a dark "cape" or coloration on their backs stretching from their head to almost mid-way between the dorsal fin and the tail flukes.

STATUS:The spotted dolphin is the species which has suffered the most in the incidental take in the purse seine nets of the tuna fishery. From 1959 to 1978, it has been estimated that over 4,000,000 spotted dolphins dies in tuna nets. For reasons unknown, yellowfin tuna and spotted dolphins travel together in the eastern tropical Pacific, an area that extends from Mexico south to Chile and west to Hawai'i and Samoa. One theory is that they feed on the same food but at different levels. Tuna fishermen watch for the dolphins, then set their nets and encircle both dolphins and tuna, killing dolphins in the process. In 1972 the Marine Mammal Protection Act was passed and through improved fishing techniques and the required practice of having government observers aboard the tuna boats to monitor the number of dolphins killed, the mortality rate dropped to about 20,000 a year in the U.S. fleet. However, these rules do not apply to foreign tuna fleets and tens of thousands of dolphins die each year in this unregulated fishery. In addition, several thousand are killed each year for food in drive fisheries in Japan.

Research:There is currently insufficient evidence to conclude that the tuna purse seine fishery is having a significant adverse impact on this or other depleted dolphin stocks in the ETP, however, much of NMFS' dolphin-related research in the ETP focuses on this population of animals. The International Dolphin Conservation Program Act (IDCPA) directed NMFS to determine if the chase and encirclement of dolphins in the purse-seine fishery for tuna in the ETP is having a significant adverse impact on depleted dolphin stocks. As part of this determination, Congress specified that population surveys be undertaken in 1998, 1999, and 2000 to generate new estimates of dolphin abundance under the IDCPA. The resulting dolphin abundance survey and other research efforts are being carried out by the NMFS Southwest Fisheries Science Center (SWFSC) on the three dolphin stocks that have been designated as depleted under the MMPA.

BIBLIOGRAPHY:Balcomb, Kenneth, and Stanley Minasian. The World's Whales. Illustrated by Larry Foster. New York: Smithsonian Books, W. W. Norton, 1984.
Leatherwood, S. and R. Reeves Whales and Dolphins San Francisco: Sierra Club Books, 1983.
Leatherwood, S., R. Reeves, W. Perrin and W. Evans. Whales, Dolphins and Porpoises of the Eastern North Pacific and Adjacent Arctic Waters. U. S. Dept. of Commerce: NOAA Technical Report, NMFS Circular 444, July 1982.

Gallery to the Spotted dolphin