Spiny dogfish (Squalus acanthias)
|Also known as:||common spinyfish, piked dogfish, white-spotted spurdog|
|Spanish:||Cazón Espinoso, Galludo, Mielga, Tiburón Espinoso, Tollo, Tolo De Cachos|
|Size||Male length: up to 100 cm (2)|
Female length: up to 124 cm (2)
The spiny dogfish is classified as Vulnerable (VU) on the IUCN Red List (1).
The common name ‘dogfish’ was given by fisherman to small sharks due to their habit of hunting shoals of fish in ‘packs’ (3). The spiny dogfish (Squalus acanthias) is a small, slim fish with a narrow, pointed snout and distinctive white spots (4). The back is slate grey to brown and the belly is pale grey to white. It has two dorsal fins, the first of which is smaller (3), both of which have a spine which can inject venom causing strong pain lasting for several hours, and very occasionally death in humans (4). The pectoral fins are curved and have rounded tips (3).
Distributed along coastlines, the spiny dogfish is found in the western Atlantic, eastern Atlantic, western Pacific and eastern Pacific, as well as the Mediterranean Sea and the Black Sea (4).
Found from the surface to a depth of 900 metres, the spiny dogfish is thought to tolerate temperatures of between 7 and 15 degrees Celsius (2) (4).
Said to be the most abundant living shark, the spiny dogfish is a slow, inactive swimmer and forms massive feeding aggregations of thousands of individuals. Tending to be same-sex and same-size shoals, they prey on shoals of bony fish, as well as octopuses, smaller sharks, squid, crabs and shark egg cases (3). They are highly migratory, moving towards the equatorial side of their range during winter (2).
With estimates of between 20 and 75 years, the spiny dogfish is thought to be a very long-lived fish that matures late and reproduces slowly, with gestation lasting two years – the longest of any vertebrate (1) (2) (3). An ovoviviparous species, spiny dogfish develop in eggs within the female, and gain nourishment from their yolk sacs, After four to six months, these eggs are shed, but the embryos continue to develop inside the female, still living off the yolk sac attached to their abdomens. Finally, after another 18 to 20 months of development, six to seven live young are born, measuring 20 to 33 centimetres (2).
Despite possessing venom-delivering spines on each of its two dorsal fins, the spiny dogfish is eaten by cod, red hake, goosefish, other spiny dogfish, larger sharks, seals, and orcas (2).
The spiny dogfish is considered to be the most abundant living shark, yet two particular subpopulations in the northwest and northeast Atlantic Ocean are considered to be at risk due to massive fishing pressure. This shark is caught for food, liver oil, and used to make sand paper, vitamins, leather, fertiliser, pet food and fish meal (1) (4). At a time of peak abundance between 1900 and 1910, it is estimated that up to 27 million spiny dogfish were caught off the Massachusetts coast every year (5).
These sharks are especially vulnerable to over-fishing as they are slow to mature, have a very long gestation period, and produce very few young. Demand for these fish is highest in Europe, but they were commonly caught in American waters for export to Europe. The American National Marine Fisheries Services closed American waters to dogfish fishing in July 2003 on evidence that the population was on the edge of collapse (2). WWF have created a suggested recovery plan that aims to reduce exploitation to very low rates to allow recovery, and to reduce by-catch by avoiding areas with spiny dogfish. Monitoring and research on the spatial and seasonal patterns of distribution are also planned (6).
Learn more about WWF’s suggested recovery plan:
WWF – A template for the development of plans to recover over-fished stocks:
For further information on the conservation of sharks and rays:
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- By-catch: in the fishing industry, the part of the catch made up of non-target species.
- Dorsal fin: the unpaired fins found on the back of the body of fish, or the raised structure on the back of most cetaceans.
- Gestation: the state of being pregnant; the period from conception to birth.
- Ovovivipary: method of reproduction whereby the egg shell is weakly formed and young hatch inside the mother; they are nourished by their yolk sac and then born.
- Pectoral fins: in fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
IUCN Red List (November, 2008)
Florida Museum of Natural History (November, 2004)
Animal Diversity Web (November, 2004)
Fish Base (November, 2004)
Fisheries Global Information System (November, 2004)
WWF – A template for the development of plans to recover over-fished stocks (November, 2004)