Tusk

Cusk are considered to be a threatened species by the Committee on the Status of Endangered Wildlife Species in Canada and a species of concern by the U.S. National Marine Fisheries service. Cusk have not yet been assessed by the IUCN. It is not considered a threatened species by CITES. Due to its decreasing population and usefulness as a food source it is garnering additional attention.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

Cusk rarely communicate with each other, and when they do it is most likely in order to locate a mate. Little is known of how this communication occurs, but it likely involves chemical signaling by females. Cusk live in deep water with little to no ambient light; their eyes are large and upturned for predator and prey detection. They have a sensory barbel on their chins that can detect vibrations, guide them over terrain, and may serve in a chemosensory capacity. They have moderately well-developed hearing and pressure sensitivity (through the lateral line system), and hunt primarily by sight, smell, or barbel detection.

Communication Channels: visual ; tactile ; chemical

Other Communication Modes: pheromones ; vibrations

Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical

The primary predators of adult cusk are humans; these fish share nearly identical habitats with Atlantic cod, a staple of the world's fishing industry. In 1987, an estimated 46,254 metric tons of cusk were caught as accidental bycatch and subsequently consumed; landings, as well as size of fish caught, have steadily decreased over the years (about 74 metric tons in U.S. waters in 2004), likely a sign of overall population decreases. Besides humans, cusk are preyed upon by sand sharks, dogfish, thorny skates, harbor seals, tuna, and porpoises. They rely on their slow movement and cryptic coloration to avoid detection by the roving predators they encounter. Additionally, the rocky substrate they inhabit allows them to seek cover in inaccessible crags if they feel threatened.

Known Predators:

• Thorny skate (Amblyraja radiata)
• Spiny dogfish (Squalus acanthias)
• Sandshark (Family Odontaspididae)
• Tuna (Thunnus orientalis)
• Harbor seal (Phoca vitulina)
• Porpoise (Family Phocoenidae)

Cusk are variable in color, with their primary dorsal coloration ranging from dark grey to a rusty or greenish brown, fading through the sides to a pale white or gray ventrally. Their vertical fins have dark margins edged in white. Adults are typically more dully-colored than juveniles, who may have six transverse yellow bands. Cusk have one long dorsal fin, one anal fin, short pectoral fins, and rounded caudal fins, as well as a chin barbel. They are easily distinguished from other members of the family Gadidae by their single dorsal fin and characteristically rounded caudal fin. Most cusk grow to be less than 100 cm in length (average 50-95 cm), with an average weight of 12 kg (maximum recorded weight 30 kg). There are no polymorphic forms or documented seasonal variations, and populations on both sides of the Atlantic are remarkably similar in size and weight, differing only slightly in color.

Range mass: 30 (high) kg.

Average mass: 12 kg.

Range length: 110 (high) cm.

Average length: 60 cm.

Other Physical Features: ectothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

Cusk can live for up to 20 years in the wild. As benthic fish that use primitive gas bladders for buoyancy, removal to the surface, with its related rapid change in pressure, is often immediately fatal. Commercial fishing is generally considered to be the greatest limiting factor in cusk longevity, as they are often by-catch of Atlantic halibut, cod, pollock, and haddock.

Typical lifespan
Status: wild: 20 (high) years.

Cusk are benthic fish, inhabiting rough-bottom areas in the cooler waters of the North Atlantic. Cusk are most often located over rocky, mud, or gravel bottoms and can be found over seamounts and knolls; they are rarely ever found over flat, sandy bottoms. A deep-water fish, cusk seldomly occur in water more shallow than 20-30 meters and are most commonly found at depths of 150-450 meters in the northeast Atlantic and from 18-149 meters in the northwest Atlantic. They can be found in waters as deep as 1,000 meters and in water temperatures from 0-10°C.

Range depth: 20 to 1000 m.

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: benthic

Cusk have a range and distribution similar to that of Atlantic cod. They are found in the northwest Atlantic Ocean from New Jersey to the Strait of Belle Isle in Canada, along the coast of Newfoundland, and occasionally off the southern tip of Greenland. In the northeast Atlantic Ocean, they are found along the coasts of Iceland, Scandinavia, and northern Ireland and England, including the northern North Sea.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); atlantic ocean (Native )

Cusks are carnivorous foragers of small fishes, crabs and other crustaceans, mollusks, starfishes, and other small, soft-bodied, benthic invertebrates. Some examples of prey items include gurnard (Family Triglidae), pea crabs (Pinnotheres pisum), caridean shrimp (Crangon crangon), and margarita snails (Margarites pupillus). They are likely opportunistic scavengers as well, scavenging freshly dead organisms, if found.

Animal Foods: fish; carrion ; mollusks; aquatic crustaceans; other marine invertebrates

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore , Scavenger )

Cusk are predators, consuming creatures that are either omnivores, detriovores, herbivores, filter feeders, or other small opportunistic carnivores. While they are not the preferred prey for any particular species, they are nonetheless occasional prey for many benthic predators and pelagic diving predators. They may be hosts to a variety of parasites, including roundworms, flatworms, and copepods.

Commensal/Parasitic Species:

• Anisakis simplex (Order Ascaridida, Phylum Nematoda)
• Pseudoterranova decipiens (Order Ascaridida, Phylum Nematoda)
• Ascaris sp. (Order Ascaridida, Phylum Nematoda)
• Prosorhynchus squamatus (Order Plagiorchiida, Class Trematoda)
• Lernaeocera lusci (Superorder Podoplea, Subclass Copepoda)

Cusk are a food item for humans. Because cusk and Atlantic cod are so similar in taste and appearance, they are often handled the same once caught and have the same pound for pound selling weight. This makes cusk both a valuable economic resource for fisheries and an important source of food for many individuals.

Positive Impacts: food

There are no known negative impacts of cusk on humans.

Females release up to 2 million buoyant eggs at a time during spawning season. Eggs hatch into planktonic young, which remain in coastal, shallow-water environments until they grow to a length of about 5 centimeters, becoming benthic thereafter. These fish have a relatively slow growth rate, reaching 22 centimeters on average by age 6 and gaining about 10 centimeters per year thereafter. Sexual maturity is achieved at about 50 centimeters in length (8-10 years of age).

Little is known about cusk mating systems, but they are assumed to be similar to that of its relative, Atlantic cod (Gadus morhua). While Atlantic cod are generally more active than cusk, they do not have rigorous courtship behaviors. A male will court a female with fin displays and "grunting," after which the female will allow the male to invert himself beneath her, where fertilization of the egg clutch occurs. Cusk are solitary outside of breeding season and are assumed to be polygynous. Spawning occurs once a year between April and July and there are spawning grounds throughout this species' range, with some notable areas between Scotland and Iceland, along the edges of the Shetland and Faeroe Islands, in the northern North Sea, and in the Gulf of Maine.

Mating System: polygynous

Breeding occurs once yearly, between April and July. Up to 2 million eggs are released and fertilized in a clutch and sexual maturity is reached at 8-10 years.

Breeding interval: Cusk breed once yearly.

Breeding season: Breeding season is from April through July.

Range number of offspring: 2 million (high) .

Range gestation period: 8 to 23 days.

Average gestation period: 15 days.

Range age at sexual or reproductive maturity (female): 8 to 10 years.

Range age at sexual or reproductive maturity (male): 8 to 10 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

There is no parental investment by either sex following egg fertilization.

Parental Investment: no parental involvement

The total catch reported in the FAO Yearbook of Fishery Statistics for 1987 is 46 601 t. Tusk is fished by Canada (3 960 t in 1987) and USA (1 390 t in 1987) in the North West Atlantic, especially in the Gulf of Maine. Off Cape Cod, it is mostly caught incidental to cod fishing. In its eastern distribution, it is mostly taken by Iceland (2 984 t), with major fishing grounds off the north coast of the British Isles, Denmark, the Northern part of the North Sea, Kattegat to Iceland, and the Murmansk coast. Along former USSR shores, it is rare and cannot be considered a commercial fish. The decreased landings of the North American fisheries in recent years are due to the change from longliningto otter trawls; tusk is not a good trawl fish since it frequents rough bottoms. Tusk is caught with otter trawls and on hard bottoms, with longlines. It is also taken in the Gulf of Maine by sportsmen fishing for groundfish in general. The total catch reported for this species to FAO for 1999 was 34 743 t. The countries with the largest catches were Norway (23 271 t) and Iceland (5 796 t). Utilization: fresh or frozen as fillets, but also dried, salted, and in brine.

The tusk lives alone or in small shoals on rough, rock, gravel, or pebble bottoms of both sides of the North Atlantic. In the Gulf of Maine, it is occasionally found on mud with hakes, and in Norwegian waters, it often lurks among gorgonian corals. Seldom found on smooth, clean sand.Generally keeps far from the shore, near the bottom, at depths from 20 to 1 000 m, mostly between 150 and 450 m in the northeastern Atlantic (except in the Faeroe Channel where it has been caught at 954 m), and between 18 and 549 m in the northwestern Atlantic. Never found near the shore or at depths of less than 20-30 m.It tolerates a temperature range from 0 to 10°C. The tusk moves little from bank to bank and there is no definite evidence of seasonal onshore or offshore migrations. While remaining in the same region, it undertakes only local migrations from greater to lesser depths. It is found alone or in small aggregations, not forming large schools such as do other gadoids. First maturity is reached at 8-10 years (50 cm length). Tusk is among the more prolific of fishes and a female of medium size can lay up to 2 million eggs which develop close to the surface. Spawning occurs in spring and early summer (April to July) on both sides of the Atlantic. Spawning grounds are distributed practically throughout the entire range, but the most important ones are between Scotland and Iceland. In the eastern Atlantic, they are located on the edge of the Shetland Islands, Faeroes and Iceland slopes, from 200 to 500 m depth, and in the northern part of the North Sea, along the 100-200 m isobaths. However, in the Gulf of Maine, the chief production of eggs probably takes place in shallower waters (but not less than 50 m) since most of the stock lives in lesser depths there. Some individuals probably even spawn close inshore in Cape Cod, Provincetown Harbour, and the Isles of Shoals. Up to 5 cm length, young are pelagic, then becoming benthic. The growth rate is slow: at age 6 the fish is about 22 cm; at 7 it varies from 26 to 37 cm; at 8 from 36 to 48 cm; and at 15 from 60 to 80 cm. It lives for a maximum of about 20 years.It feeds mostly on crustaceans and shellfishes, and also on benthic fishes (flatfishes and gurnard) and even on starfishes.

The maximum size is 110 cm although cusk is more common from 60 to 95 cm in the eastern, and from 50 to 80 cm in the western North Atlantic.

Western north Atlantic from New Jersey to the Strait of Belle Isle and on the Grand Banks of Newfoundland. Rare at the southern tip of Greenland. Found off Iceland, in the northern North Sea, and along the coasts of Scandinavia to the Murmansk Coast and at Spitzbergen.

Upper jaw slightly longer than lower. Barbel present on chin; none on snout. Single, longbased dorsal and anal fins, partly connected at their posterior ends to the rounded caudal fin; pectoral fin failing far short of anal fin origin. No elongated rays in the fleshy pelvic fin. Lateral line continuous until slightly before the caudal peduncle. Lateral line pores present on head. Colour: variable; dorsally dark red-brown or green-brown to yellow shading into pale colour on belly. Young fish may have six transverse yellow bands on sides. The most characteristic colour pattern is on the vertical fins, which have dark margin rimmed with white.

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

Sluggish. Seldom found on smooth, clean sand. Generally keeps far from shore. Forms small aggregations, but mostly solitary. Feeds on fish and invertebrates (Ref. 1371).

Dorsal spines (total): 0; Dorsal soft rays (total): 93 - 103; Analsoft rays: 62 - 75; Vertebrae: 64 - 67

Spawns in shallower waters between 40-400 m, usually 100 to 200 m. Most important spawning grounds are located between Scotland and Iceland, from 200 to 500 m depth. In the Gulf of Maine, spawning grounds can be found in shallower waters (>50 m). Some individuals even spawn close inshore in Cape Cod, Provincetown Harbor and the Isles of Shoals (Ref. 1371).

Barbel on present on chin, none on snout, its length equal to eye diameter. Color is variable; dorsally dark red-brown or green brown to yellow shading into pale color on belly. Young specimens may have six transverse yellow bands on sides. Vertical fins with dark margin rimmed with white.

Found in small shoals on rough, rock, gravel, or pebble bottoms. Generally keeps far from the shore, near the bottom, mostly between 150 and 450 m in the northeastern Atlantic, and between 18 and 550 m in the northwestern Atlantic. Occurs at a temperature range of 0°-10° C (Ref. 9988). Solitary or in small groups. Feeds on crustaceans and shellfishes, benthic fishes (flatfishes and gurnard) and even on starfishes. Preyed upon by seals (Ref. 9988). Sold fresh, frozen as fillets or dried salted. Eaten steamed, fried, broiled, boiled, microwaved and baked (Ref. 9988).

fisheries: highly commercial; gamefish: yes; price category: low; price reliability: reliable: based on ex-vessel price for this species

Brosme for sale at the fish market in Bergen, Norway, in 2012

The cusk or tusk (Brosme brosme) is a North Atlantic cod-like fish in the ling family Lotidae. It is the only species in the genus Brosme. Its other common names include torsk, European cusk, and brosmius.

Feeds on crustaceans, shellfishes, starfishes

Newfoundland to New Jersey

Found to depths of 20- 1000 m over rough, rocky or gravel bottoms.

benthic

Known from seamounts and knolls