Lamna ditropis

Occurring singly or in schools of several individuals (3), salmon sharks are long distance, high-speed predators (2), occasionally seen at or near the surface in some areas. They can maintain their body temperature well above that of the surrounding cold water of the North Pacific, and may have the highest body temperature of any shark (3). This allows them to maintain warm swimming muscles and internal organs, so they can still hunt effectively in cool waters (2). The salmon shark is considered to be one of the main predators of the Pacific salmon, and its voracious feeding on this fish has earned it its common name (3). However, it is an opportunistic feeder that consumes a wide variety of fish that also includes (amongst many others) herring, sardines, pollock, Alaska cod, lanternfishes and mackerel. It also feeds on some squid and is sometimes attracted to by-catch dumped back into the ocean by shrimp trawlers (3). After spending the summer in the north of their range, the salmon shark migrates south to breed. In the western North Pacific they migrate to Japanese waters whereas in the eastern North Pacific, the salmon shark breeds off the coast of Oregon and California, USA. The young are born in spring after a gestation period of around nine months (3). The salmon shark is ovoviviparous, and oophagy (when the growing embryos eat unfertilized eggs to gain nutrients) has been recorded in this shark (4). Most litters contain between two and five young. Male salmon sharks are thought to mature at about five years and live to at least 27 years; females reach maturity at eight to ten years and are known to live to at least 20 years (3).

This formidable hunter, which is sometimes mistaken for the white shark (Carcharodon carcharias), can be distinguished by its shorter snout and the dusky blotches that mark the white abdomen of adults (3) (4). The rest of the salmon shark's stocky, spindle-shaped body is dark bluish-grey or blackish, with white blotches around the base of the pectoral fins. The first dorsal fin is large, while the second dorsal and anal fins are tiny and are able to pivot. Its crescent-shaped tail gives it impressive propulsion through the water (2) (3), while its large, well-developed eyes enable it to spot potential prey (2), and its large, blade-like teeth are well suited to gripping slippery fish (2) (3).

A coastal-littoral and epipelagic shark that prefers boreal to cool temperate waters, from the surface to at least 152 m (Ref. 247). Common in continental offshore waters but range inshore to just off beaches (Ref. 247). Occurs singly or in schools or feeding aggregations of several individuals (Ref. 247). Feeds on fishes (Ref. 247). Ovoviviparous, embryos feeding on yolk sac and other ova produced by the mother (Ref. 50449). With up to 4 young in a litter (Ref. 247). Fast swimmer (Ref. 9988). Potentially dangerous but has never or seldom been implicated in human attacks (Ref. 247). Causes considerable damage to commercial catches and gear (Ref. 6885). Utilized fresh, dried or salted, and frozen; fins, hides and livers are also used, with fins having particular value; can be broiled and baked (Ref. 9988).

North Pacific: Japan, Korea, and the Sea of Okhotsk to the Bering Sea and southward to southern California, USA (Ref. 247) and Baja California, Mexico (Ref. 9253).

The salmon shark occurs in the North Pacific Ocean. From Japan, North Korea, South Korea and the Pacific coast of Russia, its distribution extends east to the Pacific coast of the U.S.A., Canada, and probably Mexico (3).

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 (Native ); palearctic (Native ); pacific ocean (Native )

The Salmon Shark is a coastal and oceanic inhabitant of the north and central Pacific Ocean, ranging between 35°N-65°N in the Northwest Pacific (greatest densities between 42°N-52°N) and 30°N-65°N in the northeast and eastern central Pacific (appear to be most concentrated between 50°N-60°N) (Neave and Hanavan 1960, Farquhar 1963, Compagno 1984, Blagoderov 1994, Nakano and Nagasawa 1996). They have been caught as far as 67°N and a few specimens have been taken at around 10°N (Nagasawa 1998). In general, the southern boundary of this sharks' range in the western Pacific is the transitional domain separating the subarctic current from the central Pacific current (McKinnell and Waddell 1993, Nakano and Nagasawa 1996, Nagasawa 1998). In the eastern central Pacific, Salmon Sharks occur as far south as 30°N (Croker 1942, Strasburg 1958, Hart 1973) to Baja California, Mexico (Compagno 2001).

Recent electronic tagging studies have demonstrated that the salmon shark is extremely wide ranging throughout the north Pacific with individuals traveling from Prince William Sound, Alaska into waters as far south as Baja California, Mexico and Hawaii (Weng et al. 2003, Weng et al. 2005). Bycatch of Salmon Sharks are reported in the equatorial central Pacific (Nakano and Bayliff 2003), although the authors are convinced that the reports are misidentifications since the shark is otherwise not reported in waters south of 20°N. An improved set of criteria will be used for fishery observers in the Eastern Central Pacific starting in 2004, and should help to resolve the misidentifications.

This species is abundant in water temperatures ranging from 5-18°C, and high catches have been recorded in sea surface temperatures (SST) of 9-16°C (Nakano and Nagasawa 1996).

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Northern Pacific.

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).

Range mass: 220 (high) kg.

Range length: 140 to 215 cm.

Average length: 180-210 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0

Maximum size: 3050 mm TL

305 cm TL (male/unsexed; (Ref. 247)); max. published weight: 175.0 kg (Ref. 9988)

First dorsal fin uniformly dark, no light rear tip; ventral surface of body white with dusky blotches (Ref. 247).

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.

Range depth: 1 to 255 m.

Average depth: 150 m.

Habitat Regions: temperate ; polar ; saltwater or marine

Aquatic Biomes: pelagic ; coastal

Habitat and Ecology

Systems

• Marine

Habitat Type: Marine

pelagic-oceanic; oceanodromous (Ref. 51243); marine; depth range 0 - 650 m (Ref. 50550), usually 0 - 152 m (Ref. 55221)

Depth range based on 1 specimen in 1 taxon.
Water temperature and chemistry ranges based on 1 sample.

Environmental ranges
  Depth range (m): 55 - 55
  Temperature range (°C): 0.955 - 0.955
  Nitrate (umol/L): 8.468 - 8.468
  Salinity (PPS): 33.013 - 33.013
  Oxygen (ml/l): 6.067 - 6.067
  Phosphate (umol/l): 1.445 - 1.445
  Silicate (umol/l): 26.645 - 26.645
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Depth: 0 - 152m.
Recorded at 152 meters.

Habitat: pelagic. A coastal-littoral epipelagic shark that prefers boreal to cool temperate waters, from the surface to at least 152 m. Common in continental offshore waters but may occur just off beaches. Occurs singly or in schools/feeding aggregations. Feeds on fishes like the Pacific salmon (@Oncorhynchus@), lancetfishes, daggerteeth (@Anotopterus@), sculpins, lumpfishes, Atka mackerel (@Pleurogrammus@), pollock, and tomcod. Fast swimmer (Ref. 9988). Up to 4 in a litter has been observed (Ref. 6885). Few unsubstantiated attacks but potentially dangerous. Causes considerable damage to commercial catches and gear (Ref. 6885). Utilized fresh, dried/salted, and frozen; fins, hides and livers are also used, with fins having particular value; can be broiled and baked (Ref. 9988).

This species is a coastal and oceanic shark, inhabiting waters between 2.5 and 24 degrees Celsius, generally from the surface down to depths around 152 metres, although one individual has been recorded at 255 metres (3).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

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 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.

Animal Foods: fish; carrion

Primary Diet: carnivore (Piscivore )

A carnivore (Ref. 9137).

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

Commensal/Parasitic Species:

• flatworms (Nybelinia surmenicola)
• nematodes (Anisakis simplex)
• copepods (Anthosoma crassum)
• copepods (Echthrogleus coleopteratus)
• copepods (Dinemoura latifolia)
• copepods (Dinemoura affinis)

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.

Known Predators:

• salmon sharks (Lamna ditropis)
• blue sharks (Prionace glauca)
• great white sharks (Carcharodon carcharias)
• humans (Homo sapiens)

Anti-predator Adaptations: cryptic

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 ; tactile ; acoustic ; vibrations ; chemical ; electric

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.

Exhibit ovoviparity (aplacental viviparity), with embryos feeding on other ova produced by the mother (oophagy) after the yolk sac is absorbed (Ref. 50449). Litter size is up to 4 young (Ref. 247). Distinct pairing with embrace (Ref. 205).

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.

Range lifespan
Status: wild: 17 to 25 years.

Typical lifespan
Status: wild: 20 to 30 years.

Maximum longevity: 20 years (wild)

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)

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.

Breeding interval: Females in the eastern North Pacific breed every two years, while those in the western North Pacific breed annually.

Breeding season: Breeding occurs in autumn and winter in the northern hemisphere.

Average number of offspring: 4-5.

Average gestation period: 9 months.

Range age at sexual or reproductive maturity (female): 6 to 10 years.

Range age at sexual or reproductive maturity (male): 3 to 5 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); 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 ; pre-hatching/birth (Provisioning: Female, Protecting: Female)

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.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2000
  Data Deficient

Canada

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: GNR - Not Yet Ranked

Classified as Data Deficient (DD) on the IUCN Red List (1).

Population

Population Trend

Major Threats

Least Concern (LC)

The salmon shark is often caught as by-catch in Japanese, United States and Canadian fisheries. When caught, often just the fins are taken for shark fin soup and the rest is discarded, although sometimes the flesh may be sold for consumption in Japan and the United States (4). Many fishermen view salmon sharks as pests, as they often damage fishing gear, making them more likely to be killed if captured (4). In addition to the threat of by-catch, some recreational fishing for this shark occurs in Alaskan and Canadian waters (4), and some commercial fishing has taken place in the past, such as in Prince William Sound, Alaska (5). However, the lack of population and catch data for the salmon shark means that its status, and the impact these activities may be having on the species, cannot be assessed and thus the IUCN has classified it as Data Deficient (1).

Conservation Actions

In 1997, the Alaska Board of Fisheries closed all commercial shark fishing in state waters and implemented strict regulations in the state sports fishery for salmon sharks (4). Measures such as these are vital in protecting this species' future, until further research can determine the conservation status of this magnificent predator.

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)

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

fisheries: minor commercial; gamefish: yes; price category: unknown; price reliability: