C. L. Hubbs & Follett, 1947
|Range of the salmon shark|
The salmon shark, Lamna ditropis, is a species of shark occurring in the north Pacific ocean. As an apex predator, the salmon shark feeds on salmon, squid, sablefish, and herring. Salmon sharks are remarkable for their ability to maintain body temperature, known as homeothermy, and an as-yet unexplained variability in the sex ratio between the eastern north Pacific and western north Pacific.
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. The eyes are positioned well forward, enabling binocular vision to accurately locate prey.
Salmon sharks generally grow to between 200 and 260 cm (79–103 in) in length and weigh up to 220 kg (485 lb). Males appear to reach a maximum size slightly smaller than females. Unconfirmed reports exist of salmon sharks reaching as much as 4.3 m (14.2 ft); however, the largest confirmed reports indicate a maximum total length of about 3.0 m (10 ft). The maximum reported weight of this heavily built shark is over 450 kg (992 lb).
Salmon sharks are ovoviviparous, with a litter size of two to six pups. 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 eight to 10 years, while males generally mature by age five. Reproduction timing is not well understood, but is believed to be on a two-year cycle with mating occurring in the late summer or early fall. Gestation is around 9 months. Some reports indicate the sex ratio at birth may be 2.2 males per female, but the prevalence of this is not known.
As with only a few other species of fish, salmon sharks have the ability to regulate their body temperature. This is accomplished by vascular counter-current heat exchangers, known as retia 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
It is common in continental offshore waters, but ranges inshore to just off beaches. They occur singly, in feeding aggregations of several individuals or in schools. Tagging has revealed a range which includes sub-Arctic to sub-tropical waters.
Salmon sharks occur in the northern Pacific Ocean, in both coastal waters and open ocean. They are believed to range as far south as the Sea of Japan and as far north as 65°N in Alaska and in particular in Prince William Sound during the annual salmon run. Individuals have been observed diving as deep as 668 m, but they are believed to spend most of their time in epipelagic waters.
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 their growth and development.
Currently, no commercial fishery for salmon shark exists, but 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. Fishermen deliberately injuring salmon sharks has been reported.
Sport fishermen fish for salmon sharks in Alaska. Alaskan fishing regulations limit the catch of salmon sharks to two per person per year. Sport fisherman are allowed one salmon shark per day Apr 1 - Mar 31 in British Columbia.
Although salmon sharks are thought to be capable of injuring humans, few, if any, attacks on humans have been reported, but reports of divers encountering salmon sharks and salmon sharks bumping fishing vessels have been given. These reports, however, may need positive identification of the shark species involved.
- Goldman, Kenneth; Kohin, Suzanne; Cailliet, Gregor M.; & Musick, John A. (2009). "Lamna ditropis". IUCN Red List of Threatened Species. Version 3.1. International Union for Conservation of Nature. Retrieved 11 April 2012.
- Hulbert, Leland B.; Rice, J. Stanley (December 2002). "Salmon Shark, Lamna ditropis, Movements, Diet and Abundance in the Eastern North Pacific Ocean and Prince William Sound, Alaska". Exxon Valdez Oil Spill Restoration Project 02396.
- Goldman, Kenneth; Anderson, Scot; Latour, Robert; Musick, John A. (2004). "Homeothermy in adult salmon sharks, Lamna ditropis". Environmental Biology of Fishes (Kluwer Academic Publishers) 71 (4): 403–411. doi:10.1007/s10641-004-6588-9.
- Goldman, Kenneth (August 2002). Aspects of Age, Growth, Demographics, and Thermal Biology of Two Lamniform Shark Species. PhD Dissertation, College of William and Mary, School of Marine Science.
- Goldman, Kenneth; Musick, John A. (2006). "Growth and maturity of salmon sharks (Lamna ditropis) in the eastern and western North Pacific, and comments on back-calculation methods". Fishery Bulletin 104 (2): 278–292.
- Compagno, Leonard (2001). Sharks of the World, Vol. 2. Rome, Italy: FAO.
- Nagasawa, Kazuya (1998). "Predation by Salmon Sharks (Lamna distropis) on Pacific Salmon (Oncorhynchus spp.) in the North Pacific Ocean". Bulletin of the North Pacific Anadromous Fish Commission 1: 419–432.
- Weng, Kevin C.; Pedro C. Castilho, Jeffery M. Morrissette, Ana M. Landeira-Fernandez, David B. Holts, Robert J. Schallert, Kenneth J. Goldman, Barbara A. Block (2005). "Satellite Tagging and Cardiac Physiology Reveal Niche Expansion in Salmon Sharks". Science 310: 104–106. doi:10.1126/science.1114616.
- Hulbert, Leland B.; Aires-da-Silva, Alexandre M.; Gallucci, Vincent F.; Rice, J. Stanley (2005). "Seasonal foarging movements and migratory patterns of female Lamna ditropis tagged in Prince William Sound, Alaska". Journal of Fish Biology 67 (2): 490–509. doi:10.1111/j.0022-1112.2005.00757.x.
- "Biology of the Salmon Shark". Reefquest Center for Shark Research. Retrieved 2006-09-14.
- "Fishing for Salmon Shark in Alaska". Fish Alaska Magazine. Retrieved 2006-09-14.
|Wikispecies has information related to: Lamna ditropis|
- Froese, Rainer and Pauly, Daniel, eds. (2006). "Lamna ditropis" in FishBase. May 2006 version.
- Salmon shark fact sheet
- Florida Museum of Natural History, information about salmon sharks
- TOPP, Tagging of Pacific Predators, a research group that tags salmon sharks to learn more about their habits.
- IMDB entry for Icy Killers, a wild-life documentary about salmon sharks.