|
|
Superregnum: Eukaryota Name Delphinus (Linnaeus, 1758) Vernacular names
* Delphinus on Mammal Species of the World. The Common dolphin is the name given to two species (and possibly a third) of dolphin making up the genus Delphinus. Prior to the mid-1990s, most taxonomists only recognised one species in this genus, the Common Dolphin Delphinus delphis. Modern cetologists usually recognise two species - the Short-beaked Common Dolphin, which retains the systematic name Delphinus delphis, and the Long-beaked Common Dolphin Delphinus capensis. Some studies suggest that a third species, the Arabian Common Dolphin (D. tropicalis), can be characterized by an extremely long and thin beak and found in the Red Sea and Indian Ocean. The common dolphin is not the dolphin of popular imagination despite its name; that distinction belongs to the Bottlenose Dolphin due to its widespread use in marine parks and its appearance in the television series Flipper.[3]
Both common dolphin species are medium sized dolphins, smaller than the more popular bottlenose dolphin. Adults range between 1.9 and 2.5 metres (6.2 and 8.2 ft), long, and can weigh between 80 and 235 kilograms (180 and 520 lb), although a range between 80 and 150 kilograms (180 and 330 lb) is more common.[4] Males are generally longer and heavier.[4] The color pattern on the body is unusual. The back is dark and the belly is white, while on each side is an hourglass pattern colored light grey, yellow or gold in front and dirty grey in back.[5] They have long, thin rostrums with up to 50–60 small, sharp, interlocking teeth on each side of each jaw.[6] Differentiating species Common Dolphin - Ireland Despite the historic practice of lumping the entire Delphinus genus into a single species, these widely distributed dolphins exhibit a wide variety of size, shape and colour. Indeed over the past few decades over 20 distinct species in the genus have been proposed. Scientists in California in the 1960s concluded that there were two species - the long-beaked and short-beaked. This analysis was essentially confirmed by a more in-depth genetic study in the 1990s. This study also suggested that a third species (D. tropicalis, common name usually Arabian Common Dolphin), characterized by an extremely long and thin beak and found in the Red Sea and Indian Ocean, might be distinguished from the long-beaked species. The current standard taxonomic works recognize this as just a regional variety. Natural history Common dolphins live in both warm-temperate and tropical waters worldwide between 40-60°N to 50°S. Long-beaked common dolphins prefer shallower and warmer water closer to the coast.[7] Short-beaked common dolphins are common along shelf edges and in areas with sharp bottom relief such as seamounts and escarpments.[5] Common dolphin have a varied diet consisting of many species of fish and squid. This includes mesopelagic fish and squids found in the deep scattering layer[7] They also eat epipelagic schooling species such as scombroids, elupeoids and market squids. They have been recorded to make dives up to 200 metres (660 ft) deep. Common dolphins can live in aggregations of hundreds or even thousands of dolphins.[7] They sometimes associate with other dolphin species, such as pilot whales.[7] They have also been observed bow riding on baleen whales, and they also bow ride on boats.[7] It is a fast swimmer (up to 60 km/h), and breaching behavior and aerial acrobatics are common with this species.[4] The Short-beaked common dolphin has a gestation period of 10 to 11 months.[7] The newborn calf has a length of between 70 and 100 centimetres (2.3 and 3.3 ft) and weights about 10 kilograms (22 lb).[4] For the Black Sea population, weaning occurs at between 5 and 6 months, but occurs later (up to about 19 months) in other areas.[4][7] Typical interbirth interval ranges from 1 year for the Black Sea population to 3 years for eastern Pacific Ocean populations.[7] Age of sexual maturity also varies by location, but can range between 2 and 7 years for females and 3 and 12 years for males.[4][7] There is no evidence of any major reproductive differences between the two species.[5] In captivity, the Long-beaked Common Dolphin has hybridized with the Common Bottlenose Dolphin (Tursiops truncatus).[7][8] One of the hybrids has been bred back to a bottlenose dolphin, demonstrating that such hybrids are fertile.[8] Human interactions Conservation Common dolphins face a mixture of threats due to human influence. Moderate levels of metal pollutants, which are thought to negatively impact dolphin health,[9] have been measured in some populations.[10] Populations have been hunted off the coast of Peru for use as food and shark bait. In most other areas the dolphins have not been hunted directly. Several thousand individuals have been caught in industrial trawler nets throughout their range. Common dolphins were abundant in the western Mediterranean Sea until the 1960s but occurrences there have tailed off rapidly. The reasons are not well understood but are believed to be due to extensive human activity in the area. In the U.S. they are a protected species and sometimes are caught by accident in some trawler nets as bycatch, though despite this they are still quite common throughout their range. Despite these potential threats, the Short-beaked Common Dolphin is considered to be Least Concern by the IUCN Red List, and the Long-beaked Common Dolphin is listed as Data Deficient.[1][2] Captivity Common dolphins are not common in captivity. But on at least three occasions, a beached common dolphin in California was nursed back to health at SeaWorld, San Diego but deemed unfit to release back to the ocean. These common dolphins remained at SeaWorld with the bottlenose dolphin exhibit. On one occasion a male common dolphin managed to impregnate one of the female bottlenose dolphins in the exhibit, leading to four hybrid births.[11] One of the resulting common dolphin/bottlenose dolphin hybrids remained at SeaWorld, San Diego (alternately under the name Cindy or Bullet) while the other was kept at Discovery Cove. They also participate in shows with Bottlenose Dolphin and Pilot Whale at Sea World. Other than at SeaWorld, at least 90 common dolphins are known to have been captured from the wild and kept in captivity. Captured common dolphins are said to be difficult to keep in captivity.[12] References 1. ^ a b Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. (2008). Delphinus delphis. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 7 October 2008. * Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. 231 pp. Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License |
|
