|Scientific Name:||Stenella coeruleoalba (Meyen, 1833)|
Stenella euphrosyne Gray, 1846
Stenella styx Gray, 1846
|Taxonomic Notes:||Recent genetic work suggests that the genus Stenella is paraphyletic, and it is likely that it will be restructured in coming years. This species may move to a different genus (LeDuc et al. 1999).|
|Red List Category & Criteria:||Data Deficient (Regional assessment) ver 3.1|
|Assessor(s):||Species account by IUCN SSC Cetacean Specialist Group; regional assessment by European Mammal Assessment team|
This species has a varying status in different parts of its European range. In the Mediterranean there have been population declines, and the regional population was recently assessed as Vulnerable (A4de)(Reeves and Notarbartolo di Sciara 2006). However in the eastern North Atlantic there are large populations that show no evidence of significant decline, although population trends have not been quantified. Overall in the European Mammal Assessment region, it is not possible to quantify the population trend because the relative size of the different subpopulations is not known. Consequently the species is assessed as Data Deficient at the European regional level.
|Range Description:||This is a widely-distributed species, found tropical and warm-temperate waters of the Atlantic, Pacific, and Indian oceans, as well as many adjacent seas, including the Mediterranean. Northern and southern range limits are about 50°N and 40°S, although there are extra-limital records from the Kamchatka Peninsula, southern Greenland, the Faroe Islands, and the Prince Edward Islands. They are uncommon in the Sea of Japan, East China Sea, off eastern Taiwan and Ryukyuan waters, and a few extra-limital records are known from the Persian Gulf and Red Sea.|
Native:Croatia; Cyprus; Denmark; France; Germany; Gibraltar; Greece; Iceland; Ireland; Italy; Malta; Monaco; Netherlands; Portugal; Spain; United Kingdom
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – northeast; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Indian Ocean – western; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – southeast; Pacific – northeast; Pacific – northwest; Pacific – eastern central; Pacific – western central; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Striped dolphins are the most abundant cetacean species in the Mediterranean. The population in the western Mediterranean excluding the Tyrrhenian Sea was estimated in 1991 to be 117,880 dolphins (95%CI=68,379-214,800) (Forcada et al. 1994). There is no estimate for the eastern Mediterranean Sea. Goujon (1996) conducted a sighting survey in 1993 in the fishing grounds of the albacore tuna driftnet fishery in the Bay of Biscay and estimated the abundance of striped dolphins as 74,000 individuals. |
Morphological and genetic studies strongly suggest that the Mediterranean and eastern North Atlantic populations are isolated from each other, with little or no gene flow across the Strait of Gibraltar (Calzada and Aguilar 1995, García-Martínez et al. 1995, Archer 1997, Gaspari 2004). Within the Mediterranean there is some evidence of population structure based on restriction in gene flow between areas and significant differences in tissue pollutant levels (Calzada and Aguilar 1995, Monaci et al. 1998, Gaspari 2004).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Striped dolphins are primarily found in warm temperate and tropical oceanic regions and are seen close to shore only where deep water approaches the coast (Van Waerebeek et al. 1999). In the Strait of Gibraltar, they are found in waters of 600 m or more depth (Hashmi 1990). In the Mediterranean, striped dolphins are associated with highly productive, oceanic waters beyond the continental shelf (Notarbartolo di Sciara et al. 1993, Forcada et al. 1994, Frantzis et al. 2003, Gannier 2005). |
The diet of striped dolphins consists primarily of a wide variety of small, midwater and pelagic or benthopelagic fish, especially lanternfish, cod, and squids (Wurtz and Marrale 1993, Hassani et al. 1997, Archer 2002). Striped dolphins apparently feed in pelagic to benthopelagic zones, to depths as deep as 200-700m, in continental slope or oceanic regions.
|Use and Trade:||It is sometimes used as bait in fisheries.|
In the Mediterranean small numbers were taken in Spain, France and Italy for human consumption. They were also hunted for use as bait for shrimp traps and longlines. Despite being illegal, catches continue in southern Spain and probably in other areas (SGFEN 2001, Reeves and Notarbartolo di Sciara 2006). In the Northeast Atlantic, striped dolphins were harpooned to supply food for consumption on board or to scare them away from tuna trolling lines. It is difficult to ascertain the number of dolphins taken in this way, but it has been estimated in the thousands (Reyes 1991).
Incidental catches occur throughout the range in various types of fishing gear, especially purse seines and gillnets. The high-seas drift gillnet fisheries, which operated throughout the central and western North Pacific between about 35°N and 47°N, increased during the 1970s, and peaked during the 1980s before a United Nations moratorium went into effect in January 1993. Bycatch estimates are only available for 1990, when about 3,000 striped dolphins were estimated killed (Hobbs and Jones 1993). During the 1970s and 1980s, the combined high-seas driftnet fisheries likely killed tens of thousands of striped dolphins, but this level would not have been high enough to cause population declines (Hobbs and Jones 1993).
Incidental captures in pelagic driftnets have been a major source of mortality all over the western Mediterranean in the past. These nets are still being illegally used, e.g. by Moroccan, French, Italian and Turkish vessels, resulting in extensive dolphin mortality. The Spanish driftnet fishery in the Alborán Sea reportedly killed 145-183 striped dolphins per season in the early 1990s (Silvani et al. 1999); this fishery was halted in 1995 but the nets were transferred to Moroccan boats, which continue operating and are estimated to kill in the order of 1,555-2,092 striped dolphins per year (Tudela et al. 2005). The Italian driftnet fishery has been reported to kill 5,000-15,000 dolphins, mostly striped dolphins, per year (Di Natale 1992). The French thonaille driftnet fishery has been estimated to take about 180-472 striped dolphins per season (Imbert et al. 2001). Reports from other fishing activities are sparse and collected non-systematically, but they indicate that striped dolphin mortality in at least pelagic purse-seines, longlines and gillnets is widespread and likely significant (Di Natale and Notarbartolo di Sciara 1994).
Large incidental kills in pelagic trawl and driftnet fisheries off western Europe are also a source of concern (IWC 1998, Tregenza and Collet 1998). Antoine et al. (2001) found that by-catch rates in the tuna drift-net fishery in the northeastern Atlantic were 90% composed of Delphinus delphis and Stenella coeruleoalba. Mean catch rate by trip in 1992-1993 years were 4.7 striped dolphins per km of net and per day. Such rates are similar to those estimated in other driftnet fisheries. Goujon (1996) estimated the annual additional mortality linked to driftnets in the Bay of Biscay albacore tuna fishery to 1.8% for the striped dolphin (this estimate must be increased by 30% in order to take into account the whole European albacore tuna driftnet fishery).
Tissue levels of organochlorine compounds, some heavy metals and selenium in Mediterranean striped dolphins are high and exceed threshold levels above which detrimental effects commonly appear in mammals (Monaci et al. 1998, Aguilar 2000, Cardellicchio et al. 2000). Organochlorine pollutants, in particular, are found at levels that greatly exceed thresholds of reproductive impairment in bottlenose dolphins elsewhere (Aguilar 2006). Blubber concentrations of DDT (an agricultural pesticide) and PCB, the two main organochlorine pollutants, have been slowly declining in the last two decades (Aguilar and Borrell 2005) but are still high. High PCB levels have the potential to depress reproductive rates in striped dolphins (Munson et al. 1988).
The 1990-92 epizootic devastated the whole Mediterranean population of striped dolphins, producing many thousands of deaths (Bortolotto et al. 1992, Aguilar and Raga 1993). Immediately after the event, the mean school size was found to be less than one third of prior levels, which may be interpreted as indicating a proportional reduction in overall population size (Forcada et al. 1994). The primary cause of the die-off was a morbillivirus infection (Domingo et al. 1990) but PCBs and other organochlorine pollutants with potential for immunosuppressive effects may have triggered the event or enhanced its spread and lethality (Aguilar and Borrell 1994).
Commercially exploited fish and cephalopod species are important components of striped dolphin diet in the Mediterranean (Blanco et al. 1995). As many stocks of important striped dolphin prey (e.g. the European anchovy) are known to have been depleted, reduced prey availability resulting from conflict with commercial fisheries is considered a potentially important threat (Reyes 1991, Reeves and Notarbartolo di Sciara 2006) and may have contributed to the 1990-1992 epizootic (Aguilar 2000).
|Conservation Actions:||The western Mediterranean subpopulation is included in Appendix II of the Convention on Migratory Species. Further research should be focused on stock identity and abundance, the effects of direct and incidental mortality, and the effects of pollutants and other sources of habitat disturbance on dolphin subpopulations, in particular in the western Mediterranean (Reyes 1991).|
|Citation:||Species account by IUCN SSC Cetacean Specialist Group; regional assessment by European Mammal Assessment team. 2007. Stenella coeruleoalba. The IUCN Red List of Threatened Species 2007: e.T20731A9222881.Downloaded on 15 August 2018.|
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