The salmon shark (''Lamna ditropis'') is a species of

mackerel shark The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gre ...

found in the northern

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

ocean. As an

apex predator An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...

, the salmon shark feeds on

salmon Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus '' Salmo'') and North Pacific (genus '' Onco ...

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...

sablefish The sablefish (''Anoplopoma fimbria'') is one of two members of the fish family Anoplopomatidae and the only species in the genus ''Anoplopoma''. In English, common names for it include sable (US), butterfish (US), black cod (US, UK, Canada), b ...

, and

herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Ocean ...

. It is known for its ability to maintain stomach temperature ( homeothermy), which is unusual among fish. This shark has not been demonstrated to maintain a constant body temperature. It is also known for an unexplained variability in the

sex ratio The sex ratio (or gender ratio) is usually defined as the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. Many species dev ...

between eastern and western populations in the northern Pacific.

Description

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 great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is nota ...

. The eyes are positioned well forward, enabling binocular vision to accurately locate prey. Comparison of great white shark and salmon shark

The salmon shark generally grows to between 200 and 260 cm (6.6–8.6 ft) in length and weighs 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 claims of maximum reported weight over 450 kg (992 lb) are "unsubstantiated."

Biology

Reproduction

The salmon shark is ovoviviparous, with a litter size of two to six pups. As with other

Lamniformes The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gre ...

shark species, the salmon shark is oophagous, with

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s feeding on the ova produced by the mother. Females reach sexual maturity at eight to ten 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 autumn.

Gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pr ...

is around nine months. Some reports indicate the sex ratio at birth may be 2.2 males per female, but the prevalence of this is not known.

Homeothermy

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 A rete mirabile ( Latin for "wonderful net"; plural retia mirabilia) is a complex of arteries and veins lying very close to each other, found in some vertebrates, mainly warm-blooded ones. The rete mirabile utilizes countercurrent blood flow with ...

, Latin for "wonderful nets". Arteries and veins are in extremely close proximity to each other, resulting in heat exchange. Cold blood coming from the gills to the body is warmed by blood coming from the body. This results in blood coming from the body losing its heat so that by the time it interacts with cold water from the gills, it is about the same temperature, so no heat is lost from the body to the water. Blood coming towards the body regains its heat, allowing the shark to maintain its body temperature. This minimizes heat lost to the environment, allowing salmon sharks to thrive in cold waters. Their homeothermy may also rely on SERCA2 and ryanodine receptor 2 protein expression, which may have a cardioprotective effect.

Range and distribution

It is common in continental offshore waters, but ranges from inshore to just off beaches. It occurs singly, in feeding aggregations of several individuals, or in schools. Tagging has revealed a range which includes sub-Arctic to subtropical waters. The salmon shark occurs in the North Pacific Ocean, in both coastal waters and the open ocean. It is believed to range as far south as the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, i ...

and as far north as 65°N in

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...

and in particular in Prince William Sound during the annual

salmon run ''Salmon Run'' is a 1982 video game for the Atari 8-bit family created by Bill Williams and distributed via the Atari Program Exchange. ''Salmon Run'' was the first game in Williams's career, followed by a string of successes noted for their o ...

. Individuals have been observed diving as deep as 668 m (2,192 ft), but 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 predominantly male. Whether these distinctions stem from genetically distinct

stocks Stocks are feet restraining devices that were used as a form of corporal punishment and public humiliation. The use of stocks is seen as early as Ancient Greece, where they are described as being in use in Solon's law code. The law describing ...

, or if the segregation occurs as part of their growth and development, is not known. The population differences may be a result of Japanese fishermen harvesting the male population. Japanese herbalists use the fins of males as ingredients in many traditional medicines said to treat various forms of cancer.

Human interactions

Currently, no commercial fishery for salmon shark exists, but they are occasionally caught as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

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 have 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 fishermen are allowed one salmon shark per day from April 1 to March 31 in British Columbia. The flesh of the fish is used for human consumption, and in the Japanese city of

Kesennuma, Miyagi is a city in Miyagi Prefecture, Japan. , the city had an estimated population of 59,803 and a population density of in 26,390 households. The total area of the city is . Large sections of the city were destroyed by the 2011 Tōhoku earthquake an ...

, the heart is considered a delicacy for use in

sashimi is a Japanese delicacy consisting of fresh raw fish or meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means "pierced body", i.e. " 刺身" = ''sashimi'', where 刺し = ''sashi'' (pierced, stu ...

. 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. Declines in the abundance of economically important

king salmon The Chinook salmon (''Oncorhynchus tshawytscha'') is the largest and most valuable species of Pacific salmon in North America, as well as the largest in the genus ''Oncorhynchus''. Its common name is derived from the Chinookan peoples. Other ve ...

in the 2000s may be attributed to increased predation by salmon sharks, based on remote temperature readings from tagged salmon that indicate they have been swallowed by sharks.

References

External links

*
Salmon shark fact sheet

* ttps://web.archive.org/web/20070929101900/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.
IMDB entry for Icy Killers
a wild-life documentary about salmon sharks. {{Taxonbar, from=Q74371

salmon shark The salmon shark (''Lamna ditropis'') is a species of mackerel shark found in the northern Pacific ocean. As an apex predator, the salmon shark feeds on salmon, squid, sablefish, and herring. It is known for its ability to maintain stomach tempe ...

Fish of the Bering Sea Fish of Japan Western North American coastal fauna

Apex predators