Scientific name: Brosme Brosme
The Cusk is a sedentary, slow moving, slim-bodied, cod-like fish of the western Atlantic Ocean. It is the only member of the cod family that has both a single barbel under the chin and one continuous dorsal fin. It has a rounded tail fin, small pelvic fins with four to five rays, and rounded, brush-like pectoral fins. All fins are thick and fleshy at the base. The Cusk’s colouring varies from light grey with a brown tint, with pale sides and a greyish-white belly in the northeast Atlantic, to dark reddish- or greenish-brown, or sometimes a lighter brown, with a cream or white belly in the western Atlantic. The adult reaches a maximum length of greater than 100 cm, and lives about 20 years. Eggs are buoyant and hatch larvae of 4 mm, which remain in the water column before settling to the bottom when they reach lengths of about 50 to 60 mm. Fifty percent of adults reach sexual maturity between five and six years of age (about 50 cm in length).
Distribution and Population
The Cusk is a northern species found in the Subarctic and boreal shelf waters of the North Atlantic Ocean. Its centre of abundance in the western Atlantic is between 41 and 440 N latitude, in the Gulf of Maine and the southern Scotian Shelf off southwest Nova Scotia, extending from the Fundian Channel and Browns Bank to Emerald, Western and Sable island banks. It occurs only rarely in the deep waters along the edge of the continental shelf off Newfoundland and Labrador. The Cusk has a very restricted distribution compared to other members of the cod, hake, and pollock group in the western Atlantic.
Cusk stocks straddle the Canada-United States boundary. In Canadian waters, Cusk populations are estimated to have declined by 95.5% for fish greater than 50 cm in length (size of 50% maturity) from 1970 to 2001. The population of fish greater than 50 cm in length on the Scotian Shelf is 314 520, a one order of magnitude decline since the 1970s.
The Cusk prefers rocky sea floors made up of boulders, gravel, or pebbles. It is typically found at depths of 150 to 400 m with relatively warm water temperatures of 6 to 10 oC. The fish is never found near shore or at depths less than 20 to 30 m.
The Cusk spawns in April to July, with peak spawning in late June on the Scotian Shelf. Half of the adults reach maturity at lengths of about 50 cm, or five to six years of age. The Cusk is among the most fecund (or fertile) of fish – a mature adult of more than 60 cm can have more than one million eggs. Eggs are buoyant, and hatch larvae of 4 mm, which remain in the upper water column and settle to the bottom when they reach lengths of 50 to 60 mm. There is an estimated generation time of nine years. Cusk feed on other fish species, crustaceans, and polychaetes (marine worms).
Many species take advantage of the Cusk’s slow moving habits; Spiny Dogfish, halibut, Atlantic Cod, and Hooded Seals are among its chief predators. The Cusk is sedentary and solitary, and does not form large schools. It generally remains in the same area for the duration of its life cycle.
Over-exploitation from fishing is the greatest source of mortality for Cusk. Although there is some directed fishing, the fish is mainly taken as bycatch on longlines that target Atlantic Halibut, cod, haddock, and pollock. Overall, landings of Cusk have been declining since the late 1970s, coinciding with declining lengths and weights. It is estimated that the Scotia-Fundy region has experienced a 93% decline in Cusk populations from 1970 to 2001.
The core distribution of the Cusk overlaps the Canada-United States border, and the population trends observed in both countries are similar. In the United States, most Cusk are caught in the trawl nets used by fisheries in the Gulf of Maine; there was a 60% decline in the Gulf of Maine population from 1970 to 1994.
Habitat destruction is also a threat for this species.
Courtesy of the Species at Risk Public Registry, Government of Canada