Spiny Dogfish Shark (Squalus acanthias)

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spiny dogfish near ocean floor bed

spiny_dogfishAs their name suggests, spiny dogfish sharks (Squalus acanthias) have sharp spines in front of each dorsal fin. Their bodies are dark gray above and white below, often with white spotting on the sides. They are marketed as “rock shark”, “rock cod” or “rock salmon” and are often eaten in Europe and used for English fish and chips. This species is called dogfish because they are gregarious and travel in packs of hundreds to thousands of individuals. From a morphological, experimental, fisheries, and biological perspective, it is the most written about and best known of living sharks.

Dogfish often occur in schools segregated by size and sex, although they are also found as solitary individuals. Age and length at maturity appears to vary greatly with region. In the northeast Pacific Ocean estimates of the age at maturity for female spiny dogfish have ranged from 20 years and 3 feet (92cm) to 35.5 years and 3.1 feet (94cm) (Saunders and McFarlane 1993, Bonham et al. 1949). Dogfish are believed to live 25-100 years. The females are larger than the males, and produce from 2-11 (average 7) pups that are between 8-12 inches (20-30 cm) long. They can grow to around 5 feet (1.5m) and weigh about 20 pounds (9kg). They are ovoviviparous (produce eggs that hatch within the females body) and bear live young. The gestation period is the longest of any vertebrate, about 22-24 months after a winter mating (Saunders and McFarlane 1993).

The spiny dogfish is a voracious predator that feeds primarily on bony fishes. They are known to prey heavily on schools of spawning capelin, and congregations of dogfish are often associated with herring returning to coastal waters of British Columbia. During a capelin spawning event on the Copper River flats (Alaska) during the 1998 salmon gillnet fishery, dogfish were so abundant that they often plugged gillnets and disrupted the fishery. Their principal food appears to be herring, sandlance, smelt, and euphausiids. Their diet also includes some 27 other fish species and 13 varieties of invertebrates, many of which are commercially important (Hart 1980). Dogfish are also known to prey on juvenile salmon.

spiny_dogfish1The spiny dogfish is believed to be the worlds’ most abundant shark and is the predominant shark species in Alaska. Dogfish occur in depths from the surface down to 3000 feet (900m). They are adaptable predators and are often found in brackish waters around the mouths of estuaries and feeding over tidal flats. They occur worldwide in temperate and sub-arctic waters, and in the temperate and sub-arctic latitudes of the North Atlantic and North Pacific oceans. They favor a temperature range with a minimum of 450F (70C) and a maximum of 590F (150C) and make latitudinal and depth migrations to stay within their optimum range. In the eastern Pacific Ocean they are found off Chile and from central Baja California to Alaska and to Japan. Some tagged sharks in the eastern North Pacific have traveled long distances, in one case a dogfish swam 4039 miles (6500km) to Honshu, Japan where the shark was captured 7 years after it was tagged off the coast of Washington state. One specimen was caught in a salmon gillnet during August of 1984 near Kotzebue, Alaska, far north of it’s usual range. They may occur year round in Alaskan’s southern coastal waters but are most common from spring to fall.

Spiny Dogfish Encounters in Alaska

The spiny dogfish often has a negative impact on commercial fisheries as it displaces or chases off other fishes, gets hooked or netted in gear intended for other species, damages fishing gear, and often destroys hooked and netted fishes. Spiny dogfish sharks are commonly taken by commercial fishing gear and are particularly well represented in Alaska’s pelagic trawl pollock fishery and in the longline fisheries for sablefish, halibut, Greenland turbot, and Pacific cod.

Anecdotal accounts of increasing numbers of dogfish in Prince William Sound are supported by time series of relative abundance (Catch Per Unit Effort) for dogfish compiled from International Pacific Halibut Commission longline survey data, and longline surveys conducted by the Alaska Department of Fish and Game in Prince William Sound. Spiny dogfish catch rates have increased 5-fold in Prince William Sound and 20-fold in the central Gulf of Alaska between Nuka Point and Cape St. Elias since 1994. The greatest commercial harvest rates of dogfish in the northeast Pacific are in waters off British Columbia and Washington state (see below table).

California Oregon Washington B.C. Alaska
1990 2016099   9058794
1991 2912312   6896060
1992   3350 2049778   5194091   16358
1993   6230 1697617   1829837   11945
1994   1221 152838 2111878   4003595     2425
1995     232 110742 2047815   6049484   21097
1996   1320   27053 1804234 13981713   18744
1997   8405   14517   472388   4552546   12603
1998 14976 344998   254059   5524784   12603
1999 53369 195984   245466 13000660   28074
2000 19723   88621   137284 13540792 111904
2001   6556   46779   183964   9451217 236313
2002 36259   33424 not available not available 108147
2003 not available   10047 not available not available not available

There is currently a void in our understanding of the trophic interactions between shark populations and their prey in the North Pacific Ocean. Research investigating shark ecology is needed given the evidence of an increasing abundance of sharks in near-shore waters and their potential impact on the marine ecology of the region. This work will shed light on the affects of shark populations on commercially and ecologically important prey species and will contribute to our understanding of their role as predators in the ocean.

References:
Bonham, K., F.B. Sanford, W. Clegg & G.C. Bucher 1949. Biological and vitamin A studies of dogfish landed in the State of Washington (Squalus suckleyi). Wash. Dept. Fish. Biol. Bull. 49A: 83-113.
Hart, J.L. 1973. Pacific Fishes of Canada. Bull. Fish. Res. Bd. Canada 180:44-47.
Saunders, M.W., and G.A. McFarlane 1993. Age and length at maturity of the female spiny dogfish, Squalus acanthias, in the Strait of Georgia, British Columbia, Canada. Environmental Biology of Fishes 38: 49-57, 1993.