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The Spiny Dogfish

What is the spiny dogfish?


Spiny Dogfish, Squalus acanthias, with strands of bull kelp, Macrocystis integrifolia, in background. Quadra Island off Vancouver Island, BC, Canada, (North Pacific Ocean)
Doug Perrine/Photolibrary/Getty Images

The spiny dogfish, Squalus acanthias, is a small shark. The spiny dogfish shark is the most abundant shark. This small shark is also known as the piked dogfish, skittledog, spotted dogfish, white-spotted dogfish, codshark, and thorndog. It is used as food, fertilizer, hide, pet food, and liver oil.

It has a flattened head and a snout that tapers to a blunt tip. Its mouth is full of low, flat, grinding teeth like the smooth dogfish, but the spiny dogfish also possesses an extra set of small, very strong and very sharp teeth. The smooth teeth rotate into use as needed. The first two rows are used in obtaining prey, the other rows rotate into place as they are needed. When teeth are lost, they are replaced by new teeth that rotate into place.

The fish is like its smoother cousin the dogfish, but rows of small white dots run along its grey sides and it has a sharp spine in front of each of its two dorsal fins, hence the name. The spines are poisonous.

It uses the spine defensively by curling around in a bow to strike an enemy. They are common in the Mid-Atlantic region but are considered a nuisance by commercial and sportfishermen because it has no great value on the fish market and it is easy to reel in when hooked. There is, however, an emerging European market. “Fish and chips” in Europe, for example, is usually spiny dogfish shark meat.

It grows to a length of about 3 feet but usually no longer than 4 feet.

Spiny dogfish are aggressive and have a reputation of relentlessly pursuing their prey.

The name dogfish stems from their habit of feeding in packs, numbering in the hundreds or thousands. They will eat almost anything.

The spiny dogfish is a major predator on some commercially important species such as herring, Atlantic mackerel and squid. It has been harvested for the last 100 years for its oil rich liver which was used in lamp oil and machine lubricants. The spiny dogfish is the target of a directed fishery in Atlantic Canada.

Spiny dogfish are not in demand as a food item in the United States, but they’re popular on the international market. Spiny dogfish don’t become sexually mature until 20 years old, so overfishing can be devastating to populations. Estimates of the dogfish's life span range from 25-100 years. To protect populations, quota limits were established in 2000 in waters from Maine to Florida; once the quota is filled, dogfish shark fisheries are closed for the season. Some states ban dogfish catching altogether.

It eats mostly fish, including other sharks, but also eats squid and octopus, crabs, shrimp and other invertebrates. They are gregarious and are “schooling”. Schools are sometimes segregated by sex and age. They migrate in schools, following cool waters. The spiny dogfish is an omnivorous opportunistic feeder eating whatever prey is abundant. In general their diet is comprised of capelin, cod, haddock, hake, herring, menhaden and ratfish. They also eat invertebrates such as krill, crabs, polychaete worms, jellyfish, ctenophores and amphipods.

The spiny dogfish shark stays in water that is between 45F - 59F. It will enter brackish water but not stay there for too long. They are also mostly bottom-dwellers, living from the surface to 2,500 feet. The spiny dogfish is found worldwide.

It ranges throughout the coastal waters of the Atlantic and Pacific oceans. It can be either a resident or a migrant into Canadian waters. Most move inshore in the summer and offshore in the winter, but remain in Canadian waters. It is most abundant between Nova Scotia and Cape Hatteras.

The spiny dogfish is long lived and slow growing and has an estimated life span of 30 to 40 years. Ages as old as 70 years have been determined for dogfish off British Columbia. Tagging studies have determined that some spiny dogfish can migrate great distances. Individuals tagged off of Newfoundland have been recovered in Iceland years later. There have also been records of transatlantic crossings.

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