Pantropical Spotted Dolphin
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As its common name suggests, the pantropical spotted dolphin is a spotted dolphin that occurs in tropical waters around the world. It is one of the species that fisherman tend to follow as a means of finding yellowfin tuna, which swim with them. Consequently, millions of these dolphins have been killed after becoming entangled in fishing nets. An international effort has reduced the danger in recent years by introducing dolphin-rescue techniques, limiting the accidental kill to a few thousand each year. Why the dolphins and tuna associate is unknown.
Stenella attenuata lives in the Atlantic, Indian, and Pacific oceans. It migrates seasonally to the Japanese coast and is the most common cetacean in the Gulf of Mexico.
Habitat and Ecology
Offshore spotted dolphins feed largely on small epi- and mesopelagic fishes, squids, and crustaceans that associate with the deep scattering layer (Robertson and Chivers 1997). In some areas, flying fish are also important prey. The diet of the coastal form is poorly known, but is thought to consist mainly of larger fishes, perhaps mainly bottom-living species.
The abundance estimates available total more than 2.5 million, and additional likely large populations in the Atlantic, Indian and Pacific Oceans have not been assessed. The northeastern population in the ETP declined 76% within the last three generations (69 years), but that decline has ceased and was not large enough to constitute a global decline of 30%. Large impacts of direct catch and bycatch in other regions have not been identified, and it is unlikely that the global population has been reduced by as much as 30%. Therefore, the species is assesed as Least Concern.
Spotted dolphins are also taken incidentally in local fisheries along the Central American coast (Palacios and Gerrodette 1996).
Yang et al. (1999) also reported incidental mortality in Chinese fisheries, and Dolar 1994 found incidental spotted dolphin takes in the Philippines. An unknown but suspected large number of pantropical spotted dolphins are taken by the large-mesh pelagic driftnet fishery off eastern Taiwan (J. Wang pers. comm.).
Japan takes large numbers of spotted dolphins for human consumption. The catch in 1982 was 3,799, and annual catches between 1994 and 1997 ranged from 23 to 449 (Perrin 2002). Between 1995 and 2004, the average annual catch was 129 animals (Kasuya 2007). The drive fishery for spotted dolphins began in 1959 and is thought to have caused a slight decline in the minimum age at attainment of sexual maturity in females (Kasuya 1985).
Pantropical spotted dolphins are also taken in hand-harpoon fisheries in the Philippines (Dolar et al. 1994); in Taiwan, where it is the locally preferred species of cetacean for human consumption (J. Wang pers. comm.); and regularly or opportunistically by gillnet and harpoon in India and Sri Lanka (Perrin and Hohn 1994). Drive hunts at Malaita in the Solomon Islands took several hundred or thousands of spotted dolphins annually in the 1960s; the hunts continue at present (Ross et al. 2003, Kahn 2006). Small numbers are taken in numerous small subsistence fisheries for dolphins and whales around the world, e.g. at St. Vincent in the Lesser Antilles (Perrin and Hohn 1994) and Lamalera in Indonesia (Kahn 2004). Most of these kills have not been adequately monitored and the effects on the subpopulations are usually not known.
Dolphins and small whales of several species, including S. attenuata, putatively interfere in hook-and-line fisheries for squid and yellowtail in the Iki Island region of Japan (Kishiro and Kasuya 1993). Bounties have been paid to fishermen for dolphins killed since 1957. During the period 1976-1982 a total of 538 spotted dolphins were killed. The effect of these takes on the regional population is not known.
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