Salmon shark

Taxobox
name = Salmon shark
status = DD | status_system = IUCN2.3
trend =


image_width =
regnum = Animalia
phylum = Chordata
classis = Chondrichthyes
subclassis = Elasmobranchii
ordo = Lamniformes
familia = Lamnidae
genus = "Lamna"
species = "L. ditropis"
range_

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range_map_width = 200px
range_map_caption = Range of salmon shark (in blue)
binomial = "Lamna ditropis"
binomial_authority = Hubbs and Follett, 1947The salmon shark, "Lamna ditropis", is a shark species occurring in the north Pacific ocean. As an apex predator, the salmon shark feeds on salmon, and also on squid, sablefish, and herring. [cite conference| first = Leland| last = Hulbert| coauthors = Stanley Rice| title = Salmon Shark, "Lamna ditropis", Movements, Diet and Abundance in the Eastern North Pacific Ocean and Prince William Sound, Alaska| date = December, 2002| booktitle = Exxon Valdez Oil Spill Restoration Project 02396] Salmon shark are remarkable for their ability to maintain body temperature, known as homeothermy,cite journal| last = Goldman| first = Kenneth| coauthors = Scot Anderson, Robert Latour, and John Musick| title = Homeothermy in adult salmon sharks, "Lamna ditropis"| date=2004| journal = Environmental Biology of Fishes| volume = 71| pages = 403–411| publisher = Kluwer Academic Publishers| doi = 10.1007/s10641-004-6588-9] and an as-yet unexplained variability in the sex ratio between the eastern north pacific and western north pacific cite paper| author = Goldman, Kenneth| title = Aspects of Age, Growth, Demographics, and Thermal Biology of Two Lamniform Shark Species | publisher = PhD Dissertation, College of William and Mary, School of Marine Science| date = August, 2002] .

Biology

Adult salmon sharks are medium grey to black over most of the body, with a white underside with darker blotches. Juveniles are similar in appearance but generally lack blotches. The snout is short and cone-shaped, and the overall appearance is similar to a small great white shark.

Salmon shark generally grow to between 200 and 260 cm in length and weigh up to 220 kgcite journal| last = Goldman| first = Kenneth| coauthors = John Musick| title = Growth and maturity of salmon sharks (Lamna ditropis) in the eastern and western North Pacific, and comments on back-calculation methods| journal = Fishery Bulletin| volume = 104| issue = 2| pages = 278–292| date = 2006] . Males appear to reach a maximum size which is slightly smaller than females. Unconfirmed reports exist of salmon shark reaching as much as 4.3 m however the largest confirmed reports indicate a maximum total length of approximately 3 m.

Reproduction

Salmon shark are ovoviviparous, with a litter size of 2 to 6 pups.cite book| last = Compagno| first = Leonard| title = Sharks of the World, Vol. 2| publisher = FAO| date = 2001| location = Rome, Italy| url = http://www.fao.org/fi/eims_search/advanced_s_result.asp?JOB_NO=x9293] As with other Lamniformes shark species, salmon sharks are oophagous, with embryos feeding on the ova produced by the mother.

Females reach sexual maturity at 8 to 10 years, while males generally mature by age 5.cite journal| last = Nagasawa| first = Kazuya| title = Predation by Salmon Sharks ("Lamna distropis") on Pacific Salmon ("Oncorhynchus" spp.) in the North Pacific Ocean| journal = Bulletin of the North Pacific Anadromous Fish Commission| volume = 1| pages = 419–432| date = 1998] Reproduction timing is not well understood, however it is believed to be on a two year cycle with mating occurring in the late summer or early fall. Gestation is approximately 9 months. Some reports indicate that the sex ratio at birth may be 2.2 males per female, however the prevalence of this is not known.

Homeothermy

As with only a few other species of fish, salmon shark have the ability to regulate their body temperature. This is accomplished by vascular counter-current heat exchangers, known as rete mirabilia, Latin for "wonderful nets." Blood moving toward extremities flows near colder returning blood, resulting in heat transfer. The returning blood is warmed, keeping the core of the animal heated. This ability is believed to help the salmon shark exploit prey in a wider range of water temperatures.

Range and distribution

The salmon shark is a coastal-littoral and epipelagic shark that prefers boreal to cool temperate waters. It is common in continental offshore waters but range inshore to just off beaches. They occur singly or in schools or feeding aggregations of several individuals.

Salmon shark occur in the northern Pacific Ocean, in both coastal waters and in the open ocean. Animals are believed to range as far south as the Sea of Japan and southern California, and as far north as 65 degrees north in Alaska. Individuals have been observing diving as deeply as 668 m cite journal|first=LB|last=Hulbert|coauthors=AM Aires-da-Silva, VF Gallucci, and JS Rice|title=Seasonal foarging movements and migratory patterns of female "Lamna ditropis" tagged in Prince William Sound, Alaska|journal=Journal of Fish Biology|volume = 67|date=2005|pages=490–509|doi=10.1111/j.0022-1112.2005.00757.x] , however they are believed to spend most of their time in epipelagic waters.

Regional differences

Age and sex composition differences have been observed between populations in the eastern and western North Pacific. Eastern populations are dominated by females, while the western populations are predominately male. It is not known if these distinctions stem from genetically distinct stocks, or if the segregation occurs as part of salmon shark growth and development.

Human interactions

There is no current commercial fishery for salmon shark, however, they are occasionally caught as bycatch in commercial salmon gillnet fisheries where they are usually discarded. Commercial fisheries regard salmon sharks as nuisances, since they can damage fishing gear, and consume portions of the commercial catch. There are some reports of fishermen deliberately injuring salmon sharks.cite web|title = Biology of the Salmon Shark| url=http://www.elasmo-research.org/education/shark_profiles/l_ditropis.htm| accessdate = 2006-09-14|publisher = Reefquest Center for Shark Research]

Sport fishermen fish for salmon sharks in Alaska. [cite web| title = Fishing for Salmon Shark in Alaska| publisher = Fish Alaska Magazine| url = http://www.fishalaskamagazine.com/fish/salmon_shark.htm| accessdate = 2006-09-14 ] Alaskan fishing regulations limit the catch of salmon shark to two sharks per person per year.

The flesh of the fish is utilized for human consumption, and in the Japanese city of Kesennuma, Miyagi, the heart is considered a delicacy for use in sashimi.

Although salmon sharks are thought to be capable of injuring humans, there are few if any attacks on humans. There are, however, reports of divers encountering salmon sharks as well as salmon sharks bumping fishing vessels. These reports, however, may need positive identification of the shark species involved.

References

External links

*
* [http://www.sharkinfo.ch/SI2_02e/lditropis.html Salmon shark fact sheet]
* [http://www.flmnh.ufl.edu/fish/Gallery/Descript/SalmonShark/SalmonShark.html Florida Museum of Natural History, information about salmon sharks]
* [http://www.topp.org/species/salmon_shark/ TOPP, Tagging of Pacific Predators] , a research group that tags salmon sharks to learn more about their habits.