Lamna ditropis

Geographic Range

Salmon sharks are widely distributed throughout coastal and pelagic environments within the subarctic and temperate North Pacific Ocean, between 10°N and 70°N latitude. Their range includes the Bering Sea, the Sea of Okhotsk, and the Sea of Japan, and also extends from the Gulf of Alaska to southern Baja California. Salmon sharks generally range from 35°N to 65°N latitude in the western Pacific ocean and from 30°N to 65°N in the eastern Pacific, with highest densities found between 50°N and 60°N.

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Salmon sharks are primarily pelagic, but are also found in coastal waters of the North Pacific. They generally swim in the surface layer of subarctic water, but also occur in deeper waters of warmer southern regions to at least 150m. This species appears to prefer water temperatures from 2°C to 24°C.

Populations of salmon sharks show seasonal density fluctuations in the Coastal Alaska Downwelling Region, which is characterized by turbulent mixing and strong seasonality of light and temperature. The summer-autumn usage of this ecoregion by salmon sharks coincides with the return of Pacific salmon (a preferred prey item) to their spawning rivers.

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

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

Adult salmon sharks can weigh at least 220 kg (485 lbs). There are unofficial reports of salmon sharks weighing 450 kg (992 lbs), but it is likely that this specimen was a misidentified white shark ( Carcharodon carcharias ). Sharks in the eastern North Pacific have a greater weight to length ratio than their counterparts in the western North Pacific.

When reporting shark lengths, precaudal length (PCL) is often used, even though it excludes the tail fin. This allows discussion of a standardized length measure, as different possible orientations of the tail can give different measurements of total length. The PCL is determined by calculating the straight-line-distance between two vertical lines, one projected from the tip of the snout, and the other from the precaudal point. Adult salmon sharks typically range in size from 180 to 210 cm PCL.

Most fishes are ectotherms, meaning their body temperature remains identical to the surrounding water. Salmon sharks, however, are endothermic, meaning they maintain a core body temperature higher than the surrounding water (up to 16°C). This is accomplished through retention of heat produced by cell metabolism. However, no information on the basal metabolic rate of Lamna ditropis was found.

Salmon sharks have a heavy, spindle-shaped body with a short, conical snout. These sharks have relatively long gill slits. The mouth is broadly rounded, with the upper jaw containing 28 to 30 teeth and the lower jaw containing 26 to 27 moderately large, blade-like teeth with cusplets (small bumps or “mini-teeth”) on either side of each tooth. Unpaired fins consist of a large first and much smaller second dorsal fin, a small anal fins and a crescent-shaped caudal fin. The caudal fin is homocercal, meaning the dorsal and ventral lobes are nearly equal in size. Paired fins include large pectoral fins and much smaller pelvic fins, which are modified to form reproductive structures in males. A distinctive keel is present on the caudal peduncle and a short secondary keel is present on the caudal base. Dorsal and lateral areas are dark bluish-gray to black. The belly is white, and often includes various dark paatches in adults. The ventral surface of the snout is also dark-colored.

Salmon sharks can be distinguished from great white sharks ( Carcarodon carcharias ) by the presence of a secondary keel on the caudal base, dark coloration on the ventral surface of the snout, and dusky patches on the belly, all of which are lacking in great whites. Salmon sharks are also similar in appearance to porbeagle sharks ( Lamna nasus ), but can easily be distinguished by their distributions (porbeagles are absent from the North Pacific range of salmon sharks).

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

• Sexual Dimorphism
• female larger

Development

Like other species in the family Lamnidae , only the right ovary of salmon sharks is functional. Fertilization is internal, and development proceeds within the uterus. Salmon sharks are ovoviviparous, but developing embryos maintain no direct connection to the mother to obtain nutrition. Oophagy has been observed in this species, and likely represents the primary source of nutrition for developing embryos. The pregnant female ovulates and the unfertilized eggs are sent to the nidamental gland, where they are filled with yolk. The eggs are then moved to the uterus, where the embryos can feed on them. Litters tend to contain 4 to 5 young, which are approximately 60 to 65 cm PCL at birth.

Reproduction

Little is known about how salmon sharks find and select mates, although seasonal migrations and aggregations of individuals likely facilitates this process. Males hold on to females by biting their pectoral fin during copulation, which consists of the insertion of one of the male's claspers (modified pelvic fins) into the female's cloaca. Couples have no further contact following copulation.

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

Salmon sharks mate in northern waters during autumn and give birth after a 9 month gestation period, during their southern migration in late spring through early summer. Individuals that populate the central and western North Pacific are thought to breed off the coast of Honshu, Japan. Those that populate the eastern North Pacific breed off the coasts of Oregon and California. Pups are born in nursery grounds in the central North Pacific transition zone or along the coast of United States and Canada. Female salmon sharks in the western North Pacific reproduce annually, and are estimated to bear 70 offspring in their lifetime, while evidence suggests that females in the eastern North Pacific reproduce every two years.

Sexual maturity of males in the western North Pacific is estimated to occur at approximately 140 cm PCL (corresponding to an age of 5 years), and between 170 and 180 cm (ages 8 to 10 years) for females. For salmon sharks in the eastern North Pacific, sexual maturity is reached between 125 and 145 cm PCL (ages 3 to 5 years) for males and 160 to 180 cm (ages 6 to 9) for females. Salmon sharks in both regions reach maximum lengths of approximately 215 cm PCL for females and about 190cm PCL for males.

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

Females provide nutrition to their embryos through unfertilized eggs, which are consumed by the developing young. Protection is provided to embryos through residence within the mother's uterus until they have fully developed and are able to fend for themselves.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The maximum age of salmon sharks has been estimated through vertebral analysis. In both western and eastern North Pacific populations longevity estimates are similar, between 20 and 30 years. Salmon sharks are not currently held in captivity in large oceanaria and there is no published information regarding their lifespan under captive conditions.

Behavior

Like many shark species, salmon sharks segregate by size and sex. In this species, an interesting sex ratio difference has been observed across the North Pacific basin. The western population is dominated by males whereas the eastern population is dominated by females. A north/south segregation has also been noted, with larger sharks ranging farther north than smaller ones. Salmon sharks are known to hunt both alone and in feeding aggregations of several individuals (up to 30 to 40 sharks have been observed in these schools). They are seasonal migrants, and are strongly suspected to follow the movements of preferred prey items. In the case of eastern North Pacific populations, the prey item followed appears to be Pacific salmon species, while distribution of western North Pacific populations appears to be linked to the distribution of herring and sardines . The distributional and migratory patterns of both subpopulations also appears to be influenced by the sex, size, and age of individuals.

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

Home Range

Salmon sharks are migratory predators that have no permanent territories or home ranges.

Communication and Perception

While information on intraspecific communication in salmon sharks is lacking, this species, like other cartilaginous fishes, perceives its environment using visual, olfactory, chemo- and electroreceptive, mechanical, and auditory sensory systems.

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical
• electric electric

Food Habits

The diet of salmon sharks consists of pelagic and demersal fish, mainly Pacific salmon ( Oncorhynchus species). Salmon sharks also consume steelhead trout ( Oncorhynchus mykiss ), Pacific herring ( Clupea pallasii ), sardines ( Sardinops sagax ), pollock ( Theragra chalcogramma ), lancetfishes ( Alepisaurus ferox ), daggerteeth ( Anotopterus nikparini ), Pacific sauries ( Cololabis saira ), pomfrets ( Brama japonica ), mackerel (Scombridae), lumpfishes (Cyclopteridae), sculpins (Cottidae), and other fish that they can capture.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• fish
• carrion carrion

Predation

Small salmon sharks from 70 to 110 cm PCL are at risk of being preyed upon by larger sharks, including other salmon sharks, blue sharks ( Prionace glauca ), and great white sharks ( Carcharodon carcharias ). Once maturity is reached, salmon sharks occupy the highest trophic level in the food web of subarctic waters, alongside marine mammals and seabirds. The only known predators of mature salmon sharks are humans.

Small salmon sharks are found in abundance in waters north of the subarctic boundary, which are thought to be their nursery ground. There they can avoid predation by larger sharks, which inhabit areas that are further north or south. Juveniles also display obliterate countershading, and lack the dark blotches found on the ventral areas of adults.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Salmon sharks are apex predators in subarctic waters, helping to regulate populations of their prey species within the ecosystem.

Economic Importance for Humans: Positive

Shark meat and shark fins have high economic value and salmon sharks are often caught by commercial fisheries, although this is often as bycatch in pursuit of other species. In Japan, their hearts are used for sashimi. They are also caught by sports fishermen for recreation.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Salmon sharks, when caught unintentionally as bycatch, cause problems for commercial salmon fishermen. The sharks cause damage to seines and gillnets, loss of hooked or netted salmon, and damage to trolling gear.

Salmon sharks are potentially dangerous to humans, although there are no positively documented attacks. Unsubstantiated reports of attacks by this species are likely due to misidentification of more aggressive species, such as great whites.

• Negative Impacts
• injures humans
  • bites or stings

Conservation Status

Salmon sharks are currently listed as "Data Deficient" by the IUCN Red List. Its low number of young and slow maturity may make it vulnerable to overfishing, but few fishery statistics exist for the species, and its fishery is unregulated in international waters. However, due to this lack of knowledge and the potential impact of fishing on this species' populations, heavy regulations were imposed on Alaskan sport fishing for this species in 1997.

Additional Links

Encyclopedia of Life

Contributors

Emily Lupton (author), San Diego Mesa College, Anthony Mendoza (author), San Diego Mesa College, Brian Razavinematollahi (author), San Diego Mesa College, Paul Detwiler (editor), San Diego Mesa College, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

Francis, M., L. Natanson, S. Campana. 2008. The biology and ecology of the porbeagle shark, Lamna nasus. Pp. 105-113 in Sharks of the Open Ocean: Biology, Fisheries and Conservation . Hoboken, NJ: Wiley-Blackwell.

Ganong, J., G. Shillinger. 2009. Migration of an upper trophic level predator, the salmon shark Lamna ditropis , between distant ecoregions. Marine Ecology Progress Series , 372: 253-264. Accessed October 09, 2011 at http://www.seaturtle.org/PDF/WengKC_2008_MarEcolProgSer.pdf .

Goldman, K., J. Musick. 2008. The biology and ecology of the salmon shark, Lamna ditropis. Pp. 95-104 in Sharks of the Open Ocean: Biology Fisheries and Conservation . Hoboken, NJ: Wiley-Blackwell.

Karleskint, G., R. Turner, J. Small. 2010. Introduction to Marine Biology . Belmont, Ca: Brooks/Cole, Cengage Learning.

Nagasawa, K. 1998. Predation by salmon sharks ( Lamna ditropis ) on Pacific salmon ( Oncorhynchus spp.) in the North Pacific Ocean. North Pacific Anadromous Fish Commission , Bull. No. 1: 419-433. Accessed December 06, 2011 at http://www.npafc.org/new/publications/Bulletin/Bulletin%20No.%201/page%20419-433(Nagasawa).PDF .

Roman, B. 2010. "Ichthyology at the Florida Museum of Natural History/Education Biological Profiles: Salmon Shark" (On-line). Florida Museum of Natural History. Accessed October 10, 2011 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/salmonshark/salmonshark.html .

Taylor, L. 1993. Sharks of Hawaii: Their Biology and Cultural Significance . Honolulu, Hawaii: University of Hawaii Press.

Tribuzio, C. 2004. "An investigation of the reproductive physiology of two North Pacific shark species: Spiny dogfish ( Squalus acanthias ) and salmon shark ( Lamna ditropis )" (On-line pdf). School of Aquatic and Fishery Sciences. Accessed November 09, 2011 at http://www.fish.washington.edu/research/publications/ms_phd/Tribuzio_C_MS_Sp04.pdf .

Tagging of Pacific Predators. 2010. "Tagging of Pacific Predators, Salmon Shark." (On-line). Tagging Of Pacific Predators. Accessed November 02, 2011 at http://topp.org/species/salmon_shark .