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| Striped dolphin[1] | |
|---|---|
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| A striped dolphin in full flight | |
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| Size compared to an average human | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Delphinidae |
| Genus: | Stenella |
| Species: | S. coeruleoalba |
| Binomial name | |
| Stenella coeruleoalba (Meyen, 1833) | |
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| Striped dolphin range | |
| Synonyms | |
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Thestriped dolphin (Stenella coeruleoalba) is adolphin found in temperate and tropical waters of all the world's oceans. It is a member of theoceanic dolphinfamily, Delphinidae.
The striped dolphin, also known as the euphrosyne dolphin,[4] is one of five species traditionally included in the genusStenella; however, recent genetic work by LeDucet al. (1999) indicatesStenella, as traditionally conceived, is not a natural group. According to that study, the closest relatives of the striped dolphin are theClymene dolphin, thecommon dolphins, theAtlantic spotted dolphin, andIndo-Pacific bottlenose dolphin, which was formerly considered a subspecies of thecommon bottlenose dolphin. The striped dolphin was described by Prussian physician and botanistFranz Meyen in 1833.[5]
The striped dolphin has a similar size and shape to several other dolphins that inhabit the same waters (seepantropical spotted dolphin,Atlantic spotted dolphin,Clymene dolphin).[6] However, its colouring is very different and makes it relatively easy to notice at sea. The underside is blue, white, or pink. One or two black bands circle the eyes, and then run across the back, to the flipper. These bands widen to the width of the flipper which are the same size. Two further black stripes run from behind the ear — one is short and ends just above the flipper. The other is longer and thickens along the flanks until it curves down under the belly just prior to the tail stock. Above these stripes, the dolphin's flanks are coloured light blue or grey. All appendages are black, as well. At birth, individuals weigh about 10 kg (22 lb) and are up to a meter (3 feet) long. By adulthood, they have grown to 2.4 m (7.9 ft) (females) or 2.6 m (8 ft 6 in) (males) and weigh 150 kg (330 lb) (female) or 160 kg (350 lb) (male). Research suggested sexual maturity was reached at 12 years in Mediterranean females and in the Pacific at between seven and 9 years. Longevity is about 55–60 years.Gestation lasts about 12 months, with a three- or four-year gap between calving.[7]
In common with other dolphins in its genus, the striped dolphin moves in large groups — usually up to thousands of individuals in number. Groups may be smaller in the Mediterranean andAtlantic. They may also mix with common dolphins. The striped dolphin is as capable as any dolphin at performing acrobatics — frequently breaching and jumping far above the surface of the water. Sometimes, it approaches boats in the Atlantic and Mediterranean, but this is dramatically less common in other areas, particularly in the Pacific, where it has been heavily exploited in the past. Striped dolphins are known as "streakers" throughout the eastern tropical Pacific due to their behavior of rapidly swimming away from vessels to avoid collisions.[7]
The striped dolphin feeds on smallpelagic fish andsquid.[8]
The striped dolphin inhabits temperate or tropical, off-shore waters. It is found in abundance in the North and South Atlantic Oceans, including the Mediterranean (sightings and strandings have been reported rather recently inSea of Marmara[9]) andGulf of Mexico, theIndian Ocean, and thePacific Ocean. Roughly speaking, it occupies a range running from40°N to30°S. It has been found in water temperatures ranging from 10 to 26 °C (50 to 79 °F), though the standard range is 18–22 °C (64–72 °F). In the western Pacific, where the species has been extensively studied, a distinctive migration pattern has been identified. This has not been the case in other areas. The dolphin appears to be common in all areas of its range, though that may not be continuous; areas of low population density do exist. The total population is in excess of two million. The southernmost record is of a stranded individual nearbyDunedin, southern New Zealand in 2017.[10]
Japanese whalers have hunted striped dolphins in the western Pacific since at least the 1940s. In the heyday of "striped dolphin drives", at least 8,000 to 9,000 individuals were killed each year, and in one exceptional year, 21,000 individuals were killed.[citation needed] Since the 1980s, following the introduction of quotas, this number has continued to decline, with about 200 striped dolphins hunted annually in the 2020s.[11][12] Conservationists are concerned about the Mediterranean population being threatened by pollution, disease, busy shipping lanes, and heavy incidental catches in fishing nets such as long-liners, trawlers, gill nets, trammel and purse seine nets. Recent threats include military sonar, and chemical pollution from near by harbors.[citation needed]Hydrocarbons are also a major concern such as PCBs (polychlorinated biphenyls) and HCB (hexachlorobenzene). These are said to cause problems for additional food chains, as well as a full body test to see what hydrocarbons may be passed down through parturition and lactation.[citation needed]Attempts have been made to keep the striped dolphin in captivity, but most have failed, with the exception of a few captured in Japan for the Taiji Whale Museum.[citation needed]
Striped dolphins are one of the targeted species in theTaiji dolphin drive hunt.[13]
The adult striped dolphin eats fish, squid, octopus, krill, and other crustaceans. Mediterranean striped dolphins seem to prey primarily oncephalopods (50-100% of stomach contents), while northeastern Atlantic striped dolphins most often prey on fish, frequentlylantern fish. They mainly feed on cephalopods, crustaceans, and bony fishes. They feed anywhere within the water column where prey is concentrated, and they can dive to depths of 700 m to hunt deeper-dwelling species.[14]
The eastern tropical Pacific and Mediterranean populations of the striped dolphin are listed on Appendix II[15] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), since they have an unfavorable conservation status or would benefit significantly from international co-operation organized by tailored agreements.[16]
On theIUCN Red List the striped dolphin classifies asLeast Concern despite a 30% reduction in its subpopulation over the last three generations. These dolphins may also be an indicator species for long-term monitoring ofheavy metal accumulation in the marine environment because of their importance in theJapan pelagicfood web as well as their ability to live for many years.[2]
In addition, the striped dolphin is covered by the Agreement on the Conservation of Small Cetaceans of theBaltic, North East Atlantic,Irish andNorth Seas (ASCOBANS),[17] the Agreement on the Conservation of Cetaceans in theBlack Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS),[18] the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in thePacific Islands Region (Pacific Cetaceans MOU)[19] and the Memorandum of Understanding Concerning the Conservation of theManatee and Small Cetaceans ofWestern Africa andMacaronesia (Western African Aquatic Mammals MoU)
Conservation efforts have included having ship lines take a new path to their destination such as cruise lines as well as reduced human interaction close up. Feeding the dolphins has also become a problem, and has led to behavioral changes. This has also been suggested as another reason for mortality events.[citation needed]
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The striped dolphin once thrived, numbering 127,880 before 1990. Since then, the population has suffered from incidental catches in fisheries. Mortality has been considered unsustainable, but there is a lack of data which hampers conservation efforts.[citation needed]
Various cases of stranding over the years have been a cause for alarm. With an unfavorable conservation status and the increasing amount of debris piling in the ocean every year, striped dolphin's population is decreasing. 37 dolphins stranded off the Spanish Mediterranean coast were suffering from dolphinmorbillivirus (DMV). The causes of these stranding have been changing from epizootic to enzootic.[citation needed]
Cetacean morbillivirus (CeMV) can be divided into six strains in cetaceans throughout the world, causing widespread mortality events in Europe, North America, and Australia. Studies have indicated that characteristics of CeMV may be more closely associated with disease in ruminants than carnivore species, which is representative of their evolutionary histories. Common disease presentation includes broncointerstitial pneumonia, encephalitis, lymphocytopenia, and increases in multinucleated cells. CeVM causes immunosuppression, increasing risk to secondary infection following acute resolution of clinical signs. Hypothesized transmission routes include via aerosol and trans-placentally.[citation needed]
The unusual mortality events (UMEs) among striped dolphins suggest that parasitic diseases may be increasing in the open ocean due toanthropogenic causes. In addition, case reports indicate nematodes present in the brain of the striped dolphin, described as a single round and thin worm with numerous eggs in the subcortical lesions, including the optic nerve. It is hypothesized this worm belongs to the genusContracaecum, the same genus which has been reported to infect the brains of sea lions. Caution should be employed when handling these animals due to the possibility of a serious injury if the right steps are not taken in order to ensure both human and animal safety.[citation needed]
