Brosme brosmeTorsk(Also: Tusk)

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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. (Cohen, et al., 1990; Tyus, 2012; Wootton, 1990)

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. (Bailly, 2013; Cohen, et al., 1990; Luna and Capuli, 2012; Nelson, 1994)

  • Range depth
    20 to 1000 m
    65.62 to 3280.84 ft

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. (Cohen, et al., 1990; Luna and Capuli, 2012; Nelson, 1994; Shackell, et al., 2005)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    30 (high) kg
    66.08 (high) lb
  • Average mass
    12 kg
    26.43 lb
  • Range length
    110 (high) cm
    43.31 (high) in
  • Average length
    60 cm
    23.62 in

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). (Cohen, et al., 1990; Shackell, et al., 2005; Tyus, 2012)

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. (Cohen, et al., 1990; Nelson, 1994; Tyus, 2012)

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. (Cohen, et al., 1990; Matthews, 1927)

  • Breeding interval
    Cusk breed once yearly.
  • Breeding season
    Breeding season is from April through July.
  • Range number of offspring
    2 million (high)
  • Range time to hatching
    8 to 23 days
  • Average time to hatching
    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

There is no parental investment by either sex following egg fertilization. (Cohen, et al., 1990; Shackell, et al., 2005; Tyus, 2012)

  • 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. ("Cusk (Brosme brosme)", 2009; Cohen, et al., 1990; Matthews, 1927; Nelson, 1994)

  • Typical lifespan
    Status: wild
    20 (high) years

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. (Bailly, 2013; Cohen, et al., 1990; Tyus, 2012; Wootton, 1990)

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. (Cohen, et al., 1990; Matthews, 1927)

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. (Tyus, 2012; Wootton, 1990)

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. (Bailly, 2013; Cohen, et al., 1990; Matthews, 1927; Shackell, et al., 2005; Tyus, 2012)

  • Animal Foods
  • fish
  • 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. ("Cusk (Brosme brosme)", 2009; Bailly, 2013; Cohen, et al., 1990; Matthews, 1927; Nelson, 1994)

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. ("A biological survey of the waters of Woods Hole and vicinity: Part II, Section IV: A catalogue of the marine flora", 1911; Gibson, 1996; Luna and Capuli, 2012; McDonald and Margolis, 1995; Nelson, 1994; Tyus, 2012; Wootton, 1990)

Commensal/Parasitic Species

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. (Cohen, et al., 1990; Matthews, 1927; Nelson, 1994)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known negative impacts of cusk on humans. (Cohen, et al., 1990; Matthews, 1927)

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. ("Brosme Brosme", 2012; "Cusk (Brosme brosme)", 2009; "Recovery potential assessment for Cusk (Brosme brosme)", 2008; Tyus, 2012; Wootton, 1990)

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.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scavenger

an animal that mainly eats dead animals

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Department of Commerce and Labor. A biological survey of the waters of Woods Hole and vicinity: Part II, Section IV: A catalogue of the marine flora. 31/2. Washington, D.C.: Government Printing Office. 1911. Accessed February 20, 2013 at http://books.google.com/books?id=M6BUAAAAYAAJ&pg=PA771&lpg=PA771&dq=parasite+brosme+brosme&source=bl&ots=WCcX5B-U8A&sig=hTDd_KcyaT7AI8SEcPp7r7cpwjs&hl=en&sa=X&ei=zPskUcLpO4Xy0gGq9ICoCQ&ved=0CCkQ6AEwBQ#v=onepage&q&f=false.

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.

Bailly, N. 2013. "Brosme brosme (Ascanius, 1772)" (On-line). World Register of Marine Species. Accessed February 20, 2013 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=126447.

Cohen, D., T. Inada, T. Iwamoto, N. Scialabba. 1990. FAO species catalogue vol. 10: Gadiform Fishes of the World. Rome, Italy: Publishing and Multimedia service, FAO. Accessed October 14, 2012 at http://www.fao.org/docrep/009/t0243e/t0243e00.htm.

Gibson, D. 1996. Trematoda. Pp. 373 pp. in L Margolis, Z Kabata, eds. 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.

Luna, S., E. Capuli. 2012. "Brosme brosme (Ascanius, 1772): Tusk" (On-line). Fishbase. Accessed February 20, 2013 at http://www.fishbase.org/summary/Brosme-brosme.html.

Matthews, J. 1927. Fisheries of the North Atlantic. Economic Geography, 3/1: 1-22.

McDonald, T., L. Margolis. 1995. Synopsis of the parasites of fishes of Canada: Supplement (1978-1993). Canadian Special Publication of Fisheries and Aquatic Sciences, 122: 265 pp.. Accessed February 20, 2013 at http://books.google.com/books?id=6u0Y5p-9eRUC&pg=PA98&lpg=PA98&dq=Anisakis+simplex+brosme&source=bl&ots=pvdidRcXIZ&sig=eHcIVDRpyIhbzdpStxlupgPlNi8&hl=en&sa=X&ei=SvgkUbSoJbSo0AG-3YHYCg&ved=0CBwQ6AEwAQ#v=onepage&q&f=false.

Nelson, J. 1994. Fishes of the World. Toronto: John Wiley and Sons.

Shackell, N., K. Frank, D. Brickman. 2005. Range Contraction May Not Always Predict Core Areas: An Example from Marine Fish. Ecological Applications, 15/4: 1440-1449.

Tyus, H. 2012. Ecology and Conservation of Fishes. Boca Raton, FL: CRC press.

Wootton, R. 1990. Ecology of Teleost Fishes. 29 W. 35th street, New York NY: Chapman and Hall.