Brosme brosme

Geographic Range

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 nearctic
  • native native
• palearctic palearctic
  • native native
• atlantic ocean atlantic ocean
  • native native

Habitat

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.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic

Physical Description

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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

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).

Reproduction

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 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

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

• Parental Investment
• no parental involvement

Lifespan/Longevity

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.

Behavior

Cusk are solitary bottom foragers and are sluggish, generally poor swimmers. Their activity levels are not regulated by diurnal patterns. They expend little or no energy in long distance travel, instead slowly covering expanses of territory and foraging as they pass through. They have no discernible social structure, and are social only during mating.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary

Home Range

Anecdotal evidence from fishing communities suggests that cusk do not have large home ranges. If cusk are found on new fishing grounds, they can be fished out of existence in that locality in a short period of time, with no replenishment. It is assumed that they migrate only in terms of depth, not range.

Communication and Perception

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 visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • scavenger scavenger

• Animal Foods
• fish
• carrion carrion
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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 food

Economic Importance for Humans: Negative

There are no known negative impacts of cusk on humans.

Conservation Status

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.

Additional Links

Encyclopedia of Life

Contributors

Eric Dultz (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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Gibson, D. 1996. Trematoda. Pp. 373 pp. in Guide to the parasites of fishes of Canada: Part IV , Vol. 124. Ontario, CA: NRC Monograph Publishing Program. Accessed February 20, 2013 at http://books.google.com/books?id=lt0n1ga8sr0C&pg=PA46&lpg=PA46&dq=parasite+brosme+brosme&source=bl&ots=FNttWMXF03&sig=5CFBb8xt4ymNBuvTiv3xBTJijAs&hl=en&sa=X&ei=7_kkUdvpEIjn0gHu5IG4Dg&ved=0CCYQ6AEwBA#v=onepage&q&f=false .

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2012. "Brosme Brosme" (On-line). The IUCN Red List of Threatened Species. Accessed February 20, 2013 at http://www.iucnredlist.org/search .

2009. "Cusk (Brosme brosme)" (On-line). NOAA Fisheries: Office of Protected Resources. Accessed February 20, 2013 at http://www.nmfs.noaa.gov/pr/species/fish/cusk.htm .

Canadian Science Advisory Secretariat. Recovery potential assessment for Cusk (Brosme brosme). 2008/024. Ottawa, CA: Fisheries and Oceans Canada. 2008. Accessed February 20, 2013 at http://www.dfo-mpo.gc.ca/csas/Csas/Publications/SAR-AS/2008/SAR-AS2008_024_E.pdf .