Sharks & Rays
Spiny Dogfish
Squalus acanthius and Squalus suckleyi
ALSO KNOWN AS
Spiky dog, spiked dogfish, spur dogfish, rock salmon
DISTRIBUTION
Atlantic, Pacific and eastern Indian Oceans, Mediterranean Sea, Black Sea
ECOSYSTEM/HABITAT
Coastal to offshore waters
FEEDING HABITS
Foraging predator
TAXONOMY
Order Squaliformes (dogfish & relatives); Family Squalidae (dogfish sharks)
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The spiny dogfish may go by many names, including piked dogfish, rock salmon and spiky dog, but only one truly represents this shark’s unique defense strategy. To defend itself, the spiny dogfish may inject venom into predators from the two spines at the base of each dorsal fin. Dogfish are named because fishers have observed these species chasing down smaller fish in dog-like packs. Spiny dogfish were considered one of the most abundant shark species in the ocean and, while still relatively abundant, many populations have declined. Although they are forage feeding sharks, they are relatively small and are harmless to humans. Until recently, spiny dogfish from both Canada’s Atlantic and Pacific coasts were considered the same species, however new research has classified the North Pacific spiny dogfish (Squalus suckleyi) as a separate species.
The spiny dogfish may go by many names, including piked dogfish, rock salmon and spiky dog, but only one truly represents this shark’s unique defense strategy. To defend itself, the spiny dogfish may inject venom into predators from the two spines at the base of each dorsal fin. Dogfish are named because fishers have observed these species chasing down smaller fish in dog-like packs. Spiny dogfish were considered one of the most abundant shark species in the ocean and, while still relatively abundant, many populations have declined. Although they are forage feeding sharks, they are relatively small and are harmless to humans. Until recently, spiny dogfish from both Canada’s Atlantic and Pacific coasts were considered the same species, however new research has classified the North Pacific spiny dogfish (Squalus suckleyi) as a separate species.
The spiny dogfish is a small schooling shark that forms groups of hundreds to thousands of individuals of the same sex and size. With a slender body and pointed snout, the spiny dogfish is a compact shark species reaching maximum lengths of about 100 centimetres in males and 124 centimetres in females. Their skin is grey to brown on top and becomes increasingly paler, or even white on the belly with small, irregular white spots running down each side of the body. They have two dorsal fins, each with a spine where the front of the fin meets their body, and the second dorsal fin is smaller than the first.
Spiny dogfish are ovoviviparous, which means they have eggs that grow inside the female and the young develop further in her uterus before being born as fully formed pups. They have the longest gestation period of any vertebrate, let alone any shark, which lasts about 22 to 24 months. The average spiny dogfish litter consists of five to six pups, however the number of young that are born in a litter is dependent on the size of the female. In most cases, the larger the female, the larger the litter, with some litters consisting of up to 14 pups. Males and females typically reach sexual maturity at about 10 years and 16 years respectively, but this may be as high as 35 years in some individuals.
Schools of spiny dogfish numbering in the hundreds swim close together during the day, hunting herring, mackerel and capelin, as well as squid and jellyfish in some cases. They are opportunistic feeders, however, and will not shy away from eating larger prey like cod and haddock, or smaller prey like crabs and polychaete worms . Despite possessing sharp spines on their dorsal fins, these dogfish consumes their meals by biting down on prey with sharp teeth and a strong jaw. Even as newborn pups, spiny dogfish may hunt fish two or three times their size. Predators of the spiny dogfish include larger sharks, seals, orcas, adult cod and red hake. To defend itself, the spiny dogfish may inject venom into predators from the two spines near the dorsal fins. Humans are only at risk if they improperly handle these sharks.
Spiny dogfish are targeted by longline and handline fisheries on both the Atlantic and Pacific coasts of Canada, however landings from these fisheries are considered minimal. Most spiny dogfish caught on Canada’s Atlantic coast are taken from the southwestern edge of the Scotian Shelf and in the Bay of Fundy . Spiny dogfish are frequently caught accidentally as bycatch in other fisheries and discarding of spiny dogfish is thought to be substantial. Quotas for spiny dogfish have now been put into place although better data on these populations and the number caught as bycatch is required to improve these quotas and ensure they are protecting the species.
Spiny dogfish on both of Canada’s coasts have been assessed by the Committee on the Status of Endangered Wildlife in Canada as Special Concern. While we still have a lot to learn about their populations and although they remain relatively abundant in Canadian waters, their life history traits make them vulnerable to overfishing if overfishing were to occur. With late sexual maturity, long gestation periods, slow growth and long lifespans, spiny dogfish could be at risk if their fisheries are not managed properly.
