Stenella longirostris

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. The Eastern Spinner Dolphin is listed as Vulnerable, and the Central American Spinner Dolphin and the Dwarf Spinner Dolphin have not been assessed. There are ¢. 801,000 Spinner Dolphins in the eastern tropical Pacific Ocean. The Eastern Spinner Dolphin has been impacted tuna purse-seine fisheries in the eastern tropical Pacific Ocean and currently numbers ¢. 613,000 individuals; it is recovering only at a growth rate of 1 - 1 % / year. There are 11,971 Spinner Dolphins in the northern Gulf of Mexico and 3351 individuals in Hawaiian waters. There are currently no abundance estimates for the Dwarf Spinner Dolphin. In the Philippines and Malaysia, there are ¢. 35,000 Spinner Dolphins. Many regions in the Pacific, Indian, and Atlantic oceans have not yet been surveyed, but known abundances add up to more than 1,000,000 individuals overall. Gray’s Spinner Dolphin is likely composed of several distinct populations; genetics has revealed limited gene flow among neighboring island communities in the western tropical Pacific Ocean, and even among the Hawaiian Islands gene flow is limited. The Spinner Dolphin is susceptible to tuna purse-seine fisheries in the eastern tropical Pacific Ocean. The Eastern Spinner Dolphin is estimated to have been depleted by c. 65 % since 1959 as a result of kills in this fishery. Mortality has been greatly reduced since the introduction of mortality limits by the Inter-American Tropical Tuna Commission, but the Eastern Spinner Dolphin appears to be recovering very slowly. Stress from continued fisheries encounters and mortality due to offspring separation or orphaning may be having long-term negative effects on the population. Spinner Dolphins also are taken incidentally in gillnet, trawl, and purse-seine fisheries throughout their distribution. They are the most abundant delphinid in the Indian Ocean, and annual takes in fisheries number in the hundreds per year off India and up to several thousand per year off Sri Lanka. Catch rates are unknown in other areas, including the Atlantic Ocean, especially in fisheries operating off West Africa. Incidental catches off the Philippines and Venezuela are used for shark bait and human consumption. The Spinner Dolphin is intentionally caught for these purposes in the Caribbean and off Sri Lanka, Philippines, Indonesia, and Taiwan. The Spinner Dolphin is also vulnerable to shrimp trawlers in the Gulf of Thailand. Spinner Dolphins rest in shallow bays during the day in some areas off Brazil, Hawaii, Bali, and Indonesia, and they may be increasingly susceptible to harassment from growing dolphin-watching activity.

Sumber: Delphinidae

Descriptive notes. Total length 129 - 280 cm (males) and 138 - 211 cm (females); weight up to 80 kg (males) and up to 63 kg (females). Neonates are 50 - 80 cm long and weigh 5 - 10 kg. Generally, “ Gray’s Spinner Dolphin ” (S. I. longirostris) and the “ Central American Spinner Dolphin ” (S. L centroamericana) are heavier and longer than the “ Eastern Spinner Dolphin ” (S. L orientalis). The “ Dwarf Spinner Dolphin ” (S. I. rosetventris) is smallest subspecies, as the name implies. The Spinner Dolphin has slender build; very long, thin beak; and slender curved flippers. Depending on subspecies and sex, moderately sized dorsal fins vary from falcate to triangular, with males tending to have more triangular dorsal fins. In the Eastern Spinner Dolphin, dorsal fin may be recurved, giving a look of backward placement — especially prominent in older males. Older males also have post-anal protrusion or keel, which is particularly sexually dimorphic in the Eastern Spinner Dolphin and the Central American Spinner Dolphin, but less so in Gray’s Spinner Dolphin. Adult male Eastern Spinner Dolphins and Central American Spinner Dolphins may also have upturned fluke tips. Beak tips and lips are dark gray, and bodyis three-toned, comprising a dark-gray dorsal cape, paler gray flanks, and white (pink-tinged) belly, throat, and lower jaw. The Eastern Spinner Dolphin and the Central American Spinner Dolphin are not three-toned but instead are monotone dark gray, with white patches around urogenital area and in “ armpit ” areas. There is also usually dark strip extending from eye posteroventrally to flipper joint. Another form, called the white-belly Spinner Dolphin, seems to be a hybrid between Gray’s Spinner Dolphin and the Eastern Spinner Dolphin. It is characterized by more robust build and two-tone color pattern, but sexual dimorphism is not as exaggerated as it is in the Eastern Spinner Dolphin. There may be other, more subtle morphological differences among populations. Neonates have more muted color patterns that are otherwise similar to adult patterns. There are 40 - 60 pairs of small, conical teeth in each jaw, except the Dwarf Spinner Dolphin has only 40 - 52 teeth in each jaw.

Sumber: Delphinidae