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 North Pacific they are associated with oligotrophic waters of the central North Pacific gyre and with more productive regions associated with upwelling areas in the eastern tropical Pacific and along the edges of the California and Kuroshio Current systems (Miyazaki et al. 1974; Reilly 1990; Archer and Perrin 1999; Balance et al. 2006). In the western North Atlantic, striped dolphins appear to prefer continental slope waters offshore of the Gulf Stream (Leatherwood et al. 1976; Schmidly 1981; Perrin et al. 1994). 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). Off South Africa, the species is oceanic, occurring beyond the continental shelf at depths of over 1,000 m, and its distribution is correlated with the warm Agulhas Current (Ross 1984).

The diet of the striped dolphin 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 200-700 m, in continental slope or oceanic regions.

AACCGATGACTATTCTCTACCAATCACAAAGACATTGGTACCCTATATTTACTATTTGGCGCTTGGGCAGGAATAGTAGGTACCGGTCTA---AGTTTGTTGATTCGTGCTGAATTAGGTCAACCTGGCACACTTATCGGAGAC---GACCAGCTTTATAATGTTCTAGTGACAGCTCATGCCTTCGTAATAATCTTCTTTATAGTTATACCTATCATAATTGGAGGTTTCGGGAACTGATTAGTCCCCTTAATA---ATCGGAGCCCCTGACATAGCATTCCCTCGTCTAAACAACATAAGCTTCTGACTACTCCCCCCTTCCTTTCTACTACTAATAGCATCTTCAATAATTGAGGCCGGCGCAGGTACAGGCTGAACTGTCTACCCTCCTCTAGCCGGAAATCTAGCACATGCAGGAGCCTCAGTAGACCTT---ACTATTTTCTCTCTACATTTAGCCGGTGTCTCTTCAATCCTTGGAGCTATTAACTTCATCACAACTATCATTAATATAAAACCACCCGCTATAACTCAATACCAAACACCCCTCTTCGTCTGATCAGTCTTAGTCACAGCAGTCTTACTTTTACTATCATTACCTGTTCTAGCAGCC---GGAATTACTATGCTACTAACCGATCGAAATCTAAACACAACCTTTTTCGATCCGGCAGGAGGAGGTGACCCAATCTTATATCACAACTTATTCTGATTTTTTGGCCATCCTGAAGTATATATTTTAATTCTACCCGGCTTTGGAATAATTTCACACATCGTTACTTATTATTCAGGGAAAAAA---GAACCTTTTGGGTATATGGGAATAGTATGAGCTATAGTTTCTATTGGTTTCCTAGGTTTTATTGTATGAGCTCATCATATATTCACAGTTGGAATAGACGTGGACACACGAGCATATTTTACATCAGCTACTATAATTATCGCAATTCCTACAGGAGTAAAAGTTTTCAGTTGACTA---GCAACACTTCACGGAGGA---AATATTAAATGATCTCCTGCCCTAATATGAGCTCTAGGCTTTATCTTCTTATTCACAGTAGGAGGTCTAACCGGTATCATCCTAGCTAACTCATCCTTAGATATCATCCTTCATGACACCTATTATGTAGTTGCTCATTTCCACTATGTG---CTTTCAATAGGAGCTGTCTTTGCCATCATAGGAGGCTTCGTTCACTGATTCCCACTATTTTCAGGGTATACACTCAATCCAACATGAACAAAAATTCAATTCGTAATTATATTCGTAGGTGTAAATATGACATTCTTCCCACAACACTTCCTAGGCCTATCTGGAATGCCTCGC---CGATATTCTGACTATCCAGATGCTTACACA---ACATGAAACACCATTTCATCAATAGGCTCATTTATCTCACTAACAGCAGTCATACTAATAATCTTCATTATCTGAGAAGCATTCGCATCTAAACGAGAGGTA---TTAGCGGTAGACCTCACTTCCACAAAC
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Based on sighting data in 1983-91, the total striped dolphin abundance for several populations in the western North Pacific was estimated as 570,000 (CV = 19%; Miyashita 1993). Two areas of concentration of striped dolphins in the western North Pacific were identified. The first, estimated to comprise about 52,682 animals (CV = 95%), was found between 20° and 30°N. The second, a large concentration of around 497,725 (CV = 18%) animals, was located between 30° and 40°N. Relatively few striped dolphins (about 19,631; CV = 70%) were present in the nearshore waters off Japan (Kasuya 1999). In the coastal portion of this range, the population has probably been depleted by directed takes (Kasuya 1999); however, questions of population identity remain (IWC 1994). In the eastern tropical Pacific, the most recent population estimate from a 2003 line-transect survey was 1,470,854 (CV=15%) (Gerrodette et al. 2005) Abundance estimates within 555 km (300 nautical miles) of the U. S. West Coast have averaged about 19,000 (CV = 28%) between 1991-2005 (Barlow and Forney, in press). An estimated 13,143 (CV=46%) occur in Hawaiian waters (Barlow 2006). Balance and Pitman (1998) found that S. coeruleoalba was the second-most abundant species sighted in the western tropical Indian Ocean (14% of all cetaceans, compared 33% for the eastern tropical Pacific and 10% for the Gulf of Mexico).

Striped dolphins are the most abundant cetacean in the Mediterranean. The population in the western Mediterranean excluding the Tyrrhenian Sea was estimated in 1991 to be 117,880 (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. During 2003-2004, there were an estimated 3,325 (CV=48%) in the northern Gulf of Mexico (Waring et al. 2006), and 94,462 (CV=40%) in the western North Atlantic off the US east coast (Waring et al. 2008).

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).

Unknown

The largest directed catches have occurred in Japanese waters, in drive and hand-harpoon fisheries at several locations that date back to at least the Meiji period (1868-1912). Catch statistics are incomplete before 1978, but annual recorded takes exceeded 15,000-20,000 striped dolphins in some years. Catches were reduced beginning in 1981 and have since varied between 358 (in 1987) and 4,783 (1981), averaging 2,512 during the period 1981-89. Between 1988-1994, the average catch was 1,045 (Kasuya 1999). The average take between 1995-2004 was 502 individuals (Kasuya 2007), and there has been an annual quota of 725 since 1993 (through 2006). Fragmented information on morphology, life history, pollutant levels and genetics suggests that the striped dolphins taken by Japanese fisheries are from more than one subpopulation, with varying proportions among fisheries and perhaps over time (IWC 1993).

In Taiwan, some striped dolphins are harpooned opportunistically (John Wang pers. comm.). Striped dolphins are also taken in the drive fishery at Malaita in the Solomon Islands (Ross et al. 2003) and by harpoon and gillnet in Sri Lanka and St. Vincent (Perrin et al. 1994, Ilangakoon et al. 2000a&b). Other such small indigenous fisheries may exist elsewhere.

In the Mediterranean and Northeast Atlantic 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 (Reyes 1991). Illegal catches continue in southern Spain and probably in other areas (SGFEN 2001; Aguilar 2006).

Incidental catches occur throughout the range in various types of fishing gear, especially purse seines and gillnets, including in the northeastern Indian Ocean, the eastern tropical Pacific, the north-eastern Atlantic, the Mediterranean, in the North Pacific, off the coast of Japan, and in other coastal large-mesh pelagic driftnet and pelagic longline fisheries (Archer and Perrin 1999). Bycatch probably also occurs in similar fisheries in tropical and warm-temperate waters around the world. Although rare, striped dolphins have been caught in the Natal shark nets in South Africa (Perrin et al. 1994).

High-seas drift gillnet fisheries 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 came 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. 2004). 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 (Di Natale and Notarbartolo di Sciara 1994).

Large incidental kills in pelagic trawl and driftnet fisheries off western Europe are 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 rate linked to driftnets in the Bay of Biscay albacore tuna fishery to be 1.8% for the striped dolphin. In the southwest Atlantic, by-catch of S. coeruleoalba was noted by Zerbini and Kotas (1998) off Brazil.

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 (Cardellicchio et al. 2000; Monaci et al. 1998; Aguilar 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 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). Extremely high concentrations of heavy metals, DDT and PCBs are also reported in specimens from Japan (Tanabe et al. 1983). 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). 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 (Pulcini et al. 1993; 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; Aguilar 2006) and may have contributed to the 1990-19992 epizootic (Aguilar 2000).

In 2004 and 2005, two series of unusual strandings in Taiwan included striped dolphins (Wang and Yang 2007). The cause(s) of the deaths of these animals have not been determined but it is likely that human (but non-fishing) activities were responsible. The largest directed catches have occurred in Japanese waters, in drive and hand-harpoon fisheries at several locations that date back to at least the Meiji period (1868-1912). Catch statistics are incomplete before 1978, but annual recorded takes exceeded 15,000-20,000 striped dolphins in some years. Catches were reduced beginning in 1981 and have since varied between 358 (in 1987) and 4,783 (1981), averaging 2,512 during the period 1981-89. Between 1988-1994, the average catch was 1,045 (Kasuya 1999). The average take between 1995-2004 was 502 individuals (Kasuya 2007), and there has been an annual quota of 725 since 1993 (through 2006). Fragmented information on morphology, life history, pollutant levels and genetics suggests that the striped dolphins taken by Japanese fisheries are from more than one subpopulation, with varying proportions among fisheries and perhaps over time (IWC 1993).

In Taiwan, some striped dolphins are harpooned opportunistically (J. Wang pers. comm.). Striped dolphins are also taken in the drive fishery at Malaita in the Solomon Islands (Ross et al. 2003) and by harpoon and gillnet in Sri Lanka and St. Vincent (Perrin et al. 1994, Ilangakoon et al. 2000a&b). Other such small indigenous fisheries may exist elsewhere.

In the Mediterranean and Northeast Atlantic 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 (Reyes 1991). Illegal catches continue in southern Spain and probably in other areas (SGFEN 2001; Aguilar 2006).

Incidental catches occur throughout the range in various types of fishing gear, especially purse seines and gillnets, including in the northeastern Indian Ocean, the eastern tropical Pacific, the north-eastern Atlantic, the Mediterranean, in the North Pacific, off the coast of Japan, and in other coastal large-mesh pelagic driftnet and pelagic longline fisheries (Archer and Perrin 1999). Bycatch probably also occurs in similar fisheries in tropical and warm-temperate waters around the world. Although rare, striped dolphins have been caught in the Natal shark nets in South Africa (Perrin et al. 1994).

High-seas drift gillnet fisheries 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 came 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. 2004). 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 (Di Natale and Notarbartolo di Sciara 1994).

Large incidental kills in pelagic trawl and driftnet fisheries off western Europe are 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 rate linked to driftnets in the Bay of Biscay albacore tuna fishery to be 1.8% for the striped dolphin. In the southwest Atlantic, by-catch of S. coeruleoalba was noted by Zerbini and Kotas (1998) off Brazil.

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 (Cardellicchio et al. 2000; Monaci et al. 1998; Aguilar 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 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). Extremely high concentrations of heavy metals, DDT and PCBs are also reported in specimens from Japan (Tanabe et al. 1983). 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). 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 (Pulcini et al. 1993; 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; Aguilar 2006) and may have contributed to the 1990-19992 epizootic (Aguilar 2000).

In 2004 and 2005, two series of unusual strandings in Taiwan included striped dolphins (Wang and Yang 2007). The cause(s) of the deaths of these animals have not been determined but it is likely that human (but non-fishing) activities were responsible.

The species is listed in Appendix II of CITES.

Striped dolphins are one of the main small cetacean species involved in small cetacean harpoon and drive fisheries in Japanese waters. The impact of these takes on the populations should be reassessed.

The current ban on driftnet fishing in the Mediterranean should be implemented and enforced as a matter of priority.