The spiny dogfish (Squalus acanthias), also known as the spurdog and piked dogfish, is a bottom-dwelling shark of the family Squalidae. It is a small shark, typically growing to lengths of 1.0 - 1.5 meters, and is distinguished by its slender build, greyish-brown colour (countershaded with white ventrally), dorsal white spots, heterocercal tail, lack of anal fin and characteristically, its possession of a defensive spine anterior to each dorsal fin. The species name acanthias refers to these two spines. In spite of its small size, the spiny dogfish is among the slowest-growing, latest maturing and longest lived of shark species. Males mature at around 11 years of age while females mature at around 18 - 21 years of age. They are estimated to live to up to 100 years, with Pacific animals growing slower, larger and living longer than Atlantic animals. Aplacental viviparous, they also have among the longest known gestation periods of any animal, lasting between 18 to 24 months.
The spiny dogfish is a demersal, cosmopolitan and migratory shark that inhabits temperate continental shelf seas worldwide, both in shallow coastal waters and further offshore. They can be found from the intertidal zone to depths of 900 meters, though they tend to remain mostly above 200 meters. Principal populations are found in the east and west North Atlantic, the eastern South Pacific, the South Atlantic off South America, the Cape coast of South Africa, the southern coasts of Australia and New Zealand, and in the east and west North Pacific. While the sharks are highly migratory, it is believed that little mixing occurs between populations. Movements seem to be correlated to water temperature; they favour a temperature range of between 7°C - 15°C, and make latitudinal (north-south) and depth (nearshore-offshore) migrations, possibly to stay within this range. During these journeys, they are found to travel in large, dense “packs”, segregated by size and sex.
As a consequence of its late maturity, low reproductive capacity, longevity and aggregation habit, the spiny dogfish is among the most vulnerable of shark species to overexploitation by fisheries. It has one of the lowest intrinsic rates of population increase of any marine fish and this has contributed to the sharp collapse in its numbers. Once the most abundant shark species in the world, populations of spiny dogfish have declined dramatically, with a >95 per cent decrease in Northeast Atlantic stocks and an unknown but significant decrease globally. This decline has led the IUCN to confer the shark a Vulnerable status globally and a Critically Endangered status in the Northeast Atlantic, and separately, led the CMS to list the Northern hemisphere populations on its Appendix II and Annex I of its Migratory Sharks Memorandum of Understanding. The main threats to this species are target and bycatch fisheries; its meat and fins are commercially valuable across the world and animals are caught in bottom trawls, gillnets, line gear and by rod and reel. Despite the steep population declines and awareness of its vulnerability to fishing pressures, very few conservation or management measures are in place for the spiny dogfish, though it is currently being proposed for a CITES Appendix II listing.
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