|Scientific Name:||Somniosus microcephalus|
|Species Authority:||(Bloch & Schneider, 1801)|
|Taxonomic Notes:||Yano et al. (2004) confirm that sleeper sharks found in the South Atlantic and Southern Ocean are a separate species, Somniosus antarcticus Whitley, 1939.|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor/s:||Kyne, P.M., Sherrill-Mix, S.A. & Burgess, G.H.|
|Reviewer/s:||Heupel, M.R., Simpfendorfer, C.A. & Cavanagh, R.D. (Shark Red List Authority)|
A large dogfish of the Arctic and North Atlantic, inhabiting inshore zones to continental shelves and slopes usually in depths of 0 to 1,200 m (one individual recorded at 2,200 m). Maximum size is uncertain but reaches at least 640 cm total length (TL), possibly to 730 cm TL, with most adults between 244 to 427 cm TL. This appears to be an extremely long-lived and slow-growing elasmobranch with limited reproductive capacity. Historically targeted for its liver oil in Norway, Iceland and Greenland with catches reaching 32,000 sharks/year in the 1910s in Greenland alone. These fisheries may have had a significant impact on this species, but the rate of historical decline (if any) is unknown. Presently taken as bycatch in trawl, gillnet and trap fisheries, as well as in Arctic artisanal fisheries. Its population dynamics and biology are not well understood but its large size and slow growth rate suggest it is vulnerable to fishing pressure. This shark is listed as Near Threatened on the basis of possible population declines and limiting life history characteristics. There is a need to examine historical data and monitor current bycatch levels.
|Range Description:||Restricted to Northern Atlantic and Artic regions. Reports of S. microcephalus from the Southern Hemisphere are S. antarcticus.|
Native:Canada (Labrador, New Brunswick, Nunavut, Prince Edward I.); Denmark; Germany; Greenland; Iceland; Norway; Russian Federation; United States (Maine, Massachusetts, North Carolina)
|FAO Marine Fishing Areas:||
Arctic Sea; Atlantic – northeast; Atlantic – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and Ecology:||
Littoral and epibenthic, ranging from river mouths and bays to continental shelf and slope waters. Usually found in depths of 0 to 1,200 m, but one shark was observed at 2,200 m off North Carolina (Herdendorf and Berra 1995, Compagno in prep. a). During winter months in the Arctic and boreal Atlantic, the species occurs in the intertidal zone and at the surface in shallow bays and river mouths, moving into depths of 180 to 550 m during warmer months. At lower latitudes (Gulf of Maine and North Sea) the species occurs on the continental shelves with possible movements into shallower water during spring and summer (Compagno in prep. a). Short term tracking studies of the Greenland sharks under ice off Baffin Island during late Spring suggest that individuals remained at deeper depths during the morning, gradually moving into shallower depths in the afternoon and at night (Skomal and Benz 2004). The species has been recorded in water temperatures of 0.6 to 12°C (Compagno in prep. a).
Maximum size is uncertain, but is at least 640 cm TL, possibly to 730 cm TL, however most adults are between 244 and 427 cm TL (Compagno in prep. a). Aplacental viviparous with one observed female carrying 10 young (Compagno in prep. a). Tagging studies have shown the species to be very slow growing with medium size sharks appearing to grow at a rate of 1 cm per year (Hansen 1957, Castro 1983, Castro et al. 1999).
Although reportedly sluggish, feeds on a variety of prey including invertebrates, fish, seabirds, seals as well as offal (see Compagno in prep. a for more details).
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (total length): 640?730 cm TL.
Size at birth: ~37 to 38 cm TL (Bjerkan and Koefoed 1957, Compagno in prep. a).
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: 10.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
The Greenland shark was historically targeted by shark liver fisheries in Norway, Iceland, and Greenland waters. These fisheries may have had a significant impact on this species. The Greenland fishery commenced in the very early nineteenth century. In 1857 the estimated catch was 2,000?3,000 sharks/year, but in the 1910s this had grown to 32,000 sharks/year (Jensen 1914). Commercial fishing of the Greenland shark for liver oil ceased in 1960 (Castro et al. 1999). During the 1970s the species was perceived as a problem for other fisheries in western Norway and the government subsidized a fishery in order to reduce the stock of the species (Catro et al. 1999).
Currently the species is taken as bycatch in Greenland halibut and shrimp trawl fisheries (D. Kulka, pers. comm.) and fish traps and gillnets. It is also caught by artisanal fisheries in the Arctic (Compagno in prep. a).
|Conservation Actions:||There is a need to research the historical catch data if available, to determine any population declines as a result of the fisheries. Bycatch rates in various fisheries around the Artic and north Atlantic need to be determined and monitored.|
|Citation:||Kyne, P.M., Sherrill-Mix, S.A. & Burgess, G.H. 2006. Somniosus microcephalus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 20 May 2013.|
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