Somniosus microcephalus

Geographic Range

Somniosus microcephalus is found in the north Atlantic, from the coast of New England and Canada to Scandinavian waters. They occasionally venture as far south as the mouth of the Seine River in France.

• Biogeographic Regions
• atlantic ocean atlantic ocean
  • native native

Habitat

Somniosus microcephalus live mainly on continental and insular shelves. They occupy intertidal regions in addition to some river mouths and shallow bay areas during the winter months and often move to depths from 180 to 550 meters during warmer months. They have been observed as low as 1200 meters, with one observation at 2200 meters off the coast of Georgia - extending its range both geographically and in terms of depth. In northern parts of their range, Greenland sharks are found from 0 to 1200 meters in waters from 1 to 12 degrees Celsius. In southern parts of their range, these sharks may occur at greater depths.

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

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

• Other Habitat Features
• estuarine estuarine
• intertidal or littoral intertidal or littoral

Physical Description

Somniosus microcephalus is a large, sluggish shark that averages between 2 and 4 meters in length. Most of the body is a medium grey or brown in color and sometimes exhibits dark transverse bands or small spots or blotches that are lighter or darker than the base color. The snout is short and rounded, and the body is heavy and cylindrical in shape with small precaudal fins. No spines are present in the two equally-sized dorsal fins, and the ventral lobe of the caudal fin is slightly elongated. No anal fin is present. The skin is quite rough, exhibiting denticles with curved pointed cusps. Teeth in the upper and lower jaws differ in shape; upper teeth are spear-shaped while the lower teeth are shaped with high roots and low bent cusps for slicing.

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

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

Development in Somniosus microcephalus is ovoviviparous; litters of up to ten pups have been observed. Size of fully grown young at birth has not been confirmed but is thought to be around forty centimeters. Most adults grow to between two and four meters in length.

Reproduction

Mating by this species has never been observed, but females have been found with mating scars on their caudal fins. Therefore, it is inferred that, as is the case with most sharks, males bite females until they submit. Fertilization occurs internally.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Mating has never been observed in this species and little information is available concerning reproduction in Greenland sharks or related species.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous

There is no specific information on parental investment in Greenland sharks. However, most sharks are independent immediately after birth. Females provide developing embryos with rich food sources to support their development.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

No specific information about the longevity of Somniosus microcephalus exists. Some scientists speculate that these sharks may live in excess of 100 years.

Behavior

Somniosus microcephalus is generally described as a sluggish. They spend much of their time hovering near the sea floor in search of food. They may also be capable of pursuing prey. These sharks have been observed exhibiting the behavior of animals that often prey on seals, even stalking a camera operator in one rare instance. However, no attacks on humans by this species have been confirmed. Greenland sharks are solitary, outside of the mating season or when large groups occur to exploit carrion, such as that produced by the commercial fishing industry.

• Key Behaviors
• natatorial natatorial
• motile motile
• solitary solitary

Communication and Perception

Like all sharks, Somniosus microcephalus has a lateral line which aids in the detection of movement in the surrounding waters. Sharks also have especially keen chemical perception. No communication has been observed within the species.

• Perception Channels
• tactile tactile
• vibrations vibrations
• chemical chemical
• electric electric

Food Habits

Fish, marine mammals, and carrion are three staples in the diet of Somniosus microcephalus . Fish include herring ( Clupeinae ), salmon ( Salmonidae ), smelt ( Osmeridae ), cod ( Gadidae ), pollock ( Theragra ), haddock ( Melanogrammus ), halibut ( Hippoglossus ), redfish ( Hoplostethus ), sculpins ( Cottoidei ), lumpfish ( Cyclopterus ), and skates ( Rajiformes ). Seals ( Phocidae ) and small whales ( Delphinidae ) are also common food items. Drowned horses and reindeer have also been found in the stomachs of captured specimens. Somniosus microcephalus has been observed feeding in great numbers on carrion produced by commercial whaling and fishing operations.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• mammals
• fish
• carrion carrion
• mollusks
• aquatic crustaceans
• echinoderms
• cnidarians

Predation

There are no known predators of adult Greenland sharks because of their very large size.

Ecosystem Roles

Many of these sharks have copepod parasites, Ommatokoita elongata , attached to the corneas of their eyes. A single, female copepod will attach itself to one of the corneas, resulting in corneal damage and blindness in one eye. This does not seem to negatively effect the shark, as they do not rely on their vision. It has been suggested that the bioluminescence of these parasites helps lure prey, thus resulting in a mutualistic relationship, but there is no evidence to support this.

Economic Importance for Humans: Positive

Somniosus microcephalus is commonly fished by people in the Arctic regions (Norway, Iceland, and Greenland) for its liver oil and meat. People of the Inuit tribes have also been known to use its skin to make boots and its teeth as knives.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Unless properly washed or dried, Greenland shark meat is toxic to humans. Like most sharks, Greenland sharks rarely attack unless harassed.

Conservation Status

The status of Greenland shark populations are not well known. They support a fishery for liver oil in Greenland, Norway, and Iceland, but some researcher suspect that populations have diminished. They have an estimated population doubling time of 14 years.

Other Comments

Greenland sharks are also known as sleeper sharks, ground sharks, gray sharks, and gurry sharks. They are known as ekalugssuak in Greenland, hakarl in Iceland, and hakjerring in Norway.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Patrick Mills (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

References

Compagno, L., S. Fowler. 2005. Sharks of the World . Princeton, New Jersey: Princeton University Press.

Compagno, L. 1984. FAO Species Catalogue Volume 4:Sharks of the World . Rome: United Nations Development Programme.

Eagle, D. 2006. "Biological Profiles: Greenland shark" (On-line). Florida Museum of Natural History, Ichthyology Department. Accessed February 10, 2006 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/GreenlandShark/GreenlandShark.html .

2005. "Greenland Shark and Elasmobranch Research and Education Group" (On-line). Accessed October 18, 2005 at http://www.geerg.ca .