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Salmon

Salmon (/ˈsæmən/; pl.: salmon) is the common name for several commercially important species of euryhaline ray-finned fish from the genera Salmo and Oncorhynchus of the family Salmonidae, native to tributaries of the North Atlantic (Salmo) and North Pacific (Oncorhynchus) basins. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen, all coldwater fish of the subarctic and cooler temperate regions with some sporadic endorheic populations in Central Asia.

Salmon are typically anadromous: they hatch in the shallow gravel beds of freshwater headstreams and spend their juvenile years in rivers, lakes and freshwater wetlands, migrate to the ocean as adults and live like sea fish, then return to their freshwater birthplace to reproduce. However, populations of several species are restricted to fresh waters (i.e. landlocked) throughout their lives. Folklore has it that the fish return to the exact stream where they themselves hatched to spawn, and tracking studies have shown this to be mostly true. A portion of a returning salmon run may stray and spawn in different freshwater systems; the percent of straying depends on the species of salmon.^[1] Homing behavior has been shown to depend on olfactory memory.^[2]^[3]

Salmon are important food fish and are intensively farmed in many parts of the world,^[4] with Norway being the world’s largest producer of farmed salmon, followed by Chile.^[5] They are also highly prized game fish for recreational fishing, by both freshwater and saltwater anglers. Many species of salmon have since been introduced and naturalized into non-native environments such as the Great Lakes of North America, Patagonia in South America and South Island of New Zealand.^[6]

Name and etymology

The Modern English term salmon is derived from Middle English: samoun, samon and saumon, which in turn are from Anglo-Norman: saumon, from Old French: saumon, and from Latin: salmō (which in turn might have originated from salire, meaning “to leap”.^[7]). The unpronounced “l” absent from Middle English was later added as a Latinisation to make the word closer to its Latin root. The term salmon has mostly displaced its now dialectal synonym lax, in turn from Middle English: lax, from Old English: leax, from Proto-Germanic: *lahsaz from Proto-Indo-European: *lakso-.^[8]^[9]

Species

The seven commercially important species of salmon occur in two genera of the subfamily Salmoninae. The genus Salmo contains the Atlantic salmon, found in both sides of the North Atlantic, as well as more than 40 other species commonly named as trout. The genus Oncorhynchus contains 12 recognised species which occur naturally only in the North Pacific, six of which are known as Pacific salmon while the remainder are considered trout. Outside their native habitats, Chinook salmon have been successfully introduced in New Zealand and Patagonia, while coho, sockeye and Atlantic salmon have been established in Patagonia, as well.^[10]

hideAtlantic and Pacific salmon
Genus	Image	Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
Salmo (Atlantic salmon)		Atlantic salmon	Salmo salar Linnaeus, 1758	150 cm (4 ft 11 in)	120 cm (3 ft 11 in)	46.8 kilograms (103 lb)	13 years	4.4	^[11]	^[12]	^[13]	Near threatened^[14]
Oncorhynchus (Pacific salmon)		Chinook salmon	Oncorhynchus tshawytscha (Walbaum, 1792)	150 cm (4 ft 11 in)	70 cm (2 ft 4 in)	61.4 kilograms (135 lb)	9 years	4.4	^[15]	^[16]	^[17]	Not assessed
		Chum salmon	Oncorhynchus keta (Walbaum, 1792)	100 cm (3 ft 3 in)	58 cm (1 ft 11 in)	15.9 kilograms (35 lb)	7 years	3.5	^[18]	^[19]	^[20]	Not assessed
		Coho salmon	Oncorhynchus kisutch (Walbaum, 1792)	108 cm (3 ft 7 in)	71 cm (2 ft 4 in)	15.2 kilograms (34 lb)	5 years	4.2	^[21]	^[22]	^[23]	Not assessed
		Masu salmon	Oncorhynchus masou (Brevoort, 1856)	79 cm (2 ft 7 in)	50 cm (1 ft 8 in)	10.0 kilograms (22.0 lb)	3 years	3.6	^[24]		^[25]	Not assessed
		Pink salmon	Oncorhynchus gorbuscha (Walbaum, 1792)	76 cm (2 ft 6 in)	50 cm (1 ft 8 in)	6.8 kilograms (15 lb)	3 years	4.2	^[26]	^[27]	^[28]	Not assessed
		Sockeye salmon	Oncorhynchus nerka (Walbaum, 1792)	84 cm (2 ft 9 in)	58 cm (1 ft 11 in)	7.7 kilograms (17 lb)	8 years	3.7	^[29]	^[30]	^[31]	Least concern^[32]

^† Both the Salmo and Oncorhynchus genera also contain a number of trout species informally referred to as salmon. Within Salmo, the Adriatic salmon (Salmo obtusirostris) and Black Sea salmon (Salmo labrax) have both been named as salmon in English, although they fall outside the generally recognized seven salmon species. The masu salmon (Oncorhynchus masou) is actually considered a trout (“cherry trout”) in Japan, with masu actually being the Japanese word for trout. On the other hand, the steelhead and sea trout, the anadromous forms of rainbow trout and brown trout respectively, are from the same genera as salmon and live identical migratory lives, but neither is termed “salmon” .

Commercial fish
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The extinct Eosalmo driftwoodensis, the oldest known Salmoninae fish in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor. The Eocene salmon’s fossil from British Columbia provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred 10 to 20 million years ago during the Miocene. This independent evidence from DNA analysis and the fossil record indicate that salmon divergence occurred long before the Quaternary glaciation began the cycle of glacial advance and retreat.^[33]

Non-salmon species of “salmon”

There are several other species of fish which are colloquially called “salmon” but are not true salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid closely related (from the same subfamily) to the seven species of salmon above, but others are fishes of unrelated orders, given the common name “salmon” simply due to similar shapes, behaviors and niches occupied:

hideSome other fishes called salmon
Common name	Scientific name	Order	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Fish Base	FAO	ITIS	IUCN status
Australian salmon	Arripis trutta (Forster, 1801)	Perciformes	89 cm (2 ft 11 in)	47 cm (1 ft 7 in)	9.4 kilograms (21 lb)	26 years	4.1	^[34]		^[35]	Not assessed
Danube salmon	Hucho hucho (Linnaeus, 1758)	Salmoniformes	150 cm (4 ft 11 in)	70 cm (2 ft 4 in)	52 kilograms (115 lb)	15 years	4.2	^[36]		^[37]	Endangered^[38]
Hawaiian salmon	Elagatis bipinnulata (Quoy & Gaimard, 1825)	Carangiformes	180 cm (5 ft 11 in)	90 cm (2 ft 11 in)	46.2 kilograms (102 lb)	6 years	3.6	^[39]	^[40]	^[41]	Not assessed
Indian salmon	Eleutheronema tetradactylum (Shaw, 1804)	Perciformes	200 cm (6 ft 7 in)	50 cm (1 ft 8 in)	145 kilograms (320 lb)	years	4.4	^[42]		^[43]	Not assessed

Distribution

Pacific salmon leaping at Willamette Falls, Oregon

Commercial production of salmon in million tonnes 1950–2010^[44]

Atlantic salmon (Salmo salar) reproduce in northern rivers on both coasts of the Atlantic Ocean.
- Landlocked Atlantic salmon (Salmo salar m. sebago) is a potamodromous (migratory only between fresh waters) subspecies/morph that live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Onega, Ladoga, Saimaa, Vänern and Winnipesaukee. They are not a different species from the sea-run Atlantic salmon but have independently evolved a freshwater-only life cycle, which they maintain even when they could access the ocean.
Chinook salmon (Oncorhynchus tshawytscha) are also known in the United States as king salmon or “blackmouth salmon”, and as “spring salmon” in British Columbia, Canada. Chinook salmon is the largest of all Pacific salmon, frequently exceeding 6 ft (1.8 m) and 14 kg (30 lb).^[45] The name tyee is also used in British Columbia to refer to Chinook salmon over 30 pounds and in the Columbia River watershed, especially large Chinooks were once referred to as June hogs. Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic,^[46] and as far south as the Central Californian Coast.^[47]
Chum salmon (Oncorhynchus keta) is known as dog salmon or calico salmon in some parts of the US, and as keta in the Russian Far East. This species has the widest geographic range of the Pacific species:^[48] in the eastern Pacific from north of the Mackenzie River in Canada to south of the Sacramento River in California and in the western Pacific from Lena River in Siberia to the island of Kyūshū in the Sea of Japan.
Coho salmon (Oncorhynchus kisutch) are also known in the US as silver salmon. This species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California (Monterey Bay).^[49] It is also now known to occur, albeit infrequently, in the Mackenzie River.^[46]
Masu salmon (Oncorhynchus masou), also known as “cherry trout” (桜鱒サクラマス, sakura masu) in Japan, are found only in the western Pacific Ocean in Japan, Korea, and Russian Far East. A landlocked subspecies known as the Taiwanese salmon or Formosan salmon (Oncorhynchus masou formosanus) is found in central Taiwan’s Chi Chia Wan Stream.^[50]
Pink salmon (Oncorhynchus gorbuscha), known as humpback salmon or “humpies” in southeast and southwest Alaska, are found in the western Pacific from Lena River in Siberia to Korea, found throughout northern Pacific, and in the eastern Pacific from the Mackenzie River in Canada^[46] to northern California, usually in shorter coastal streams. It is the smallest of the Pacific species, with an average weight of 1.6 to 1.8 kg (3.5 to 4.0 lb).^[51]
Sockeye salmon (Oncorhynchus nerka) is also known as red salmon in the US (especially Alaska).^[52] This lake-rearing species is found in the eastern Pacific from Bathurst Inlet in the Canadian Arctic to Klamath River in California, and in the western Pacific from the Anadyr River in Siberia to northern Hokkaidō island in Japan. Although most adult Pacific salmon feed on small fish, shrimp, and squid, sockeye feed on plankton they filter through gill rakers.^[53] Kokanee salmon are the landlocked form of sockeye salmon.
Danube salmon, or huchen (Hucho hucho), are the largest permanent freshwater salmonid species.

Life cycle

See also: Salmon run and Juvenile salmon

Eggs in different stages of development: In some, only a few cells grow on top of the yolk, in the lower right, the blood vessels surround the yolk, and in the upper left, the black eyes are visible, even the little lens.

Salmon fry hatching—the baby has grown around the remains of the yolk—visible are the arteries spinning around the yolk and small oil drops, also the gut, the spine, the main caudal blood vessel, the bladder, and the arcs of the gills.

Salmon eggs are laid in freshwater streams typically at high latitudes. The eggs hatch into alevin or sac fry. The fry quickly develop into parr with camouflaging vertical stripes. The parr stay for six months to three years in their natal stream before becoming smolts, which are distinguished by their bright, silvery colour with scales that are easily rubbed off. Only 10% of all salmon eggs are estimated to survive to this stage.^[54]

The smolt body chemistry changes, allowing them to live in salt water. While a few species of salmon remain in fresh water throughout their life cycle, the majority are anadromous and migrate to the ocean for maturation: in these species, smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to osmoregulation in the ocean. This body chemistry change is hormone-driven, causing physiological adjustments in the function of osmoregulatory organs such as the gills, which leads to large increases in their ability to secrete salt.^[55] Hormones involved in increasing salinity tolerance include insulin-like growth factor I, cortisol, and thyroid hormones,^[56] which permits the fish to endure the transition from a freshwater environment to the ocean.

The salmon spend about one to five years (depending on the species) in the open ocean, where they gradually become sexually mature. The adult salmon then return primarily to their natal streams to spawn. Atlantic salmon spend between one and four years at sea. When a fish returns after just one year’s sea feeding, it is called a grilse in Canada, Britain, and Ireland. Grilse may be present at spawning, and go unnoticed by large males, releasing their own sperm on the eggs.^[57]

Prior to spawning, depending on the species, salmon undergo changes. They may grow a hump, develop canine-like teeth, or develop a kype (a pronounced curvature of the jaws in male salmon). All change from the silvery blue of a fresh-run fish from the sea to a darker colour. Salmon can make amazing journeys, sometimes moving hundreds of miles upstream against strong currents and rapids to reproduce. Chinook and sockeye salmon from central Idaho, for example, travel over 1,400 km (900 mi) and climb nearly 2,100 m (7,000 ft) from the Pacific Ocean as they return to spawn. Condition tends to deteriorate the longer the fish remain in fresh water, and they then deteriorate further after they spawn, when they are known as kelts. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. Between 2 and 4% of Atlantic salmon kelts survive to spawn again, all females. However, even in those species of salmon that may survive to spawn more than once (iteroparity), postspawning mortality is quite high (perhaps as high as 40 to 50%).

To lay her roe, the female salmon uses her tail (caudal fin), to create a low-pressure zone, lifting gravel to be swept downstream, excavating a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering 2.8 m² (30 sq ft).^[58] The eggs usually range from orange to red. One or more males approach the female in her redd, depositing sperm, or milt, over the roe.^[53] The female then covers the eggs by disturbing the gravel at the upstream edge of the depression before moving on to make another redd. The female may make as many as seven redds before her supply of eggs is exhausted.^[53]

Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in ring formation around an earbone called the otolith (annuli), analogous to the growth rings visible in a tree trunk. Freshwater growth shows as densely crowded rings, sea growth as widely spaced rings; spawning is marked by significant erosion as body mass is converted into eggs and milt.

Freshwater streams and estuaries provide important habitat for many salmon species. They feed on terrestrial and aquatic insects, amphipods, and other crustaceans while young, and primarily on other fish when older. Eggs are laid in deeper water with larger gravel and need cool water and good water flow (to supply oxygen) to the developing embryos. Mortality of salmon in the early life stages is usually high due to natural predation and human-induced changes in habitat, such as siltation, high water temperatures, low oxygen concentration, loss of stream cover, and reductions in river flow. Estuaries and their associated wetlands provide vital nursery areas for the salmon prior to their departure to the open ocean. Wetlands not only help buffer the estuary from silt and pollutants, but also provide important feeding and hiding areas.

Salmon not killed by other means show greatly accelerated deterioration (phenoptosis, or “programmed aging”) at the end of their lives. Their bodies rapidly deteriorate right after they spawn as a result of the release of massive amounts of corticosteroids.

Juvenile salmon, parr, grow up in the relatively protected natal river
The parr lose their camouflage bars and become smolt as they become ready for the transition to the ocean.
Male ocean-phase adult sockeye
Male spawning-phase adult sockeye

Diet

Salmon are mid-level carnivores whose diet change according to their life stage. Salmon fry predominantly feed upon zooplanktons until they reach fingerling sizes, when they start to consume more aquatic invertebrates such as insect larvae, microcrustaceans and worms. As juveniles (parrs), they become more predatory and actively prey upon aquatic insects, small crustaceans, tadpoles and small bait fishes. They are also known to breach the water to attack terrestrial insects such as grasshoppers and dragonflies,^[59] as well as consuming fish eggs (even those of other salmon).

As adults, salmon behave like other mid-sized pelagic fish, eating a variety of sea creatures including smaller forage fish such as lanternfish, herrings, sand lances, mackerels and barracudina. They also eat krill, squid and polychaete worms.^[60]

Ecology

Bears

Grizzly bears function as ecosystem engineers, capturing salmon and carrying them into adjacent dry land to eat the fish. There they deposit nutrient-rich urine and feces and partially eaten carcasses. Bears preparing for hibernation tend to preferentially consume the more nutrient- and energy-rich salmon roes and brain over the actual flesh,^[62] and are estimated to discard up to half the salmon they’ve harvested uneaten on the forest floor,^[63]^[64] in densities that can reach 4,000 kg (8,800 lb) per hectare,^[65] providing as much as 24% of the total nitrogen available to the riparian woodlands. The foliage of spruce trees up to 500 m (1,600 ft) from a stream where grizzlies fish salmon have been found to contain nitrogen originating from the fished salmon.^[66]

Beavers

Beavers also function as ecosystem engineers; in the process of tree-cutting and damming, beavers alter the local ecosystems extensively. Beaver ponds can provide critical habitat for juvenile salmon.

An example of this was seen in the years following 1818 in the Columbia River Basin. In 1818, the British government made an agreement with the U.S. government to allow U.S. citizens access to the Columbia catchment (see Treaty of 1818). At the time, the Hudson’s Bay Company sent word to trappers to extirpate all furbearers from the area in an effort to make the area less attractive to U.S. fur traders. In response to the elimination of beavers from large parts of the river system, salmon runs plummeted, even in the absence of many of the factors usually associated with the demise of salmon runs. Salmon recruitment can be affected by beavers’ dams because dams can:^[67]^[68]^[69]

Slow the rate at which nutrients are flushed from the water system; nutrients provided by adult salmon dying throughout the fall and winter remain available in the spring to newly hatched juveniles
Provide deeper salmon pools where young salmon can avoid avian predators
Increase productivity through algal photosynthesis and by enhancing the conversion efficiency of the cellulose-powered detritus cycle^{[clarification needed]}
Create slow-water environments where juvenile salmon put the food they ingest into growth rather than into fighting currents
Increase structural complexity with many physical niches where salmon can avoid predators

Beaver dams are able to nurture salmon juveniles in estuarine tidal marshes where the salinity is less than 10 ppm. Beavers build small dams of generally less than 60 cm (2 ft) high in channels in the myrtle zone^{[clarification needed]}. These dams can be overtopped at high tide and hold water at low tide. This provides refuges for juvenile salmon so they do not have to swim into large channels where they are subject to predation by larger fish.^[70]

Lampreys

It has been discovered that rivers which have seen a decline or disappearance of anadromous lampreys, loss of the lampreys also affects the salmon in a negative way. Like salmon, anadromous lampreys stop feeding and die after spawning, and their decomposing bodies release nutrients into the stream. Also, along with species like rainbow trout and Sacramento sucker, lampreys clean the gravel in the rivers during spawning.^[71] Their larvae, called ammocoetes, are filter feeders which contribute to the health of the waters. They are also a food source for the young salmon, and being fattier and oilier, it is assumed predators prefer them over salmon offspring, taking off some of the predation pressure on smolts.^[72]^{[unreliable source?]} Adult lampreys are also the preferred prey of seals and sea lions, which can eat 30 lampreys to every salmon, allowing more adult salmon to enter the rivers to spawn without being eaten by the marine mammals.^[73]^[74]

Parasites

Main article: Diseases and parasites in salmon

According to Canadian biologist Dorothy Kieser, the myxozoan parasite Henneguya salminicola is commonly found in the flesh of salmonids. It has been recorded in the field samples of salmon returning to the Haida Gwaii Islands. The fish responds by walling off the parasitic infection into a number of cysts that contain milky fluid. This fluid is an accumulation of a large number of parasites.

Henneguya and other parasites in the myxosporean group have complex life cycles, where the salmon is one of two hosts. The fish releases the spores after spawning. In the Henneguya case, the spores enter a second host, most likely an invertebrate, in the spawning stream. When juvenile salmon migrate to the Pacific Ocean, the second host releases a stage infective to salmon. The parasite is then carried in the salmon until the next spawning cycle. The myxosporean parasite that causes whirling disease in trout has a similar life cycle.^[75] However, as opposed to whirling disease, the Henneguya infestation does not appear to cause disease in the host salmon—even heavily infected fish tend to return to spawn successfully.

According to Dr. Kieser, a lot of work on Henneguya salminicola was done by scientists at the Pacific Biological Station in Nanaimo in the mid-1980s, in particular, an overview report^[76] which states, “the fish that have the longest fresh water residence time as juveniles have the most noticeable infections. Hence in order of prevalence, coho are most infected followed by sockeye, chinook, chum and pink. As well, the report says, at the time the studies were conducted, stocks from the middle and upper reaches of large river systems in British Columbia such as Fraser, Skeena, Nass and from mainland coastal streams in the southern half of B.C., “are more likely to have a low prevalence of infection.” The report also states, “It should be stressed that Henneguya, economically deleterious though it is, is harmless from the view of public health. It is strictly a fish parasite that cannot live in or affect warm blooded animals, including man”.

According to Klaus Schallie, Molluscan Shellfish Program Specialist with the Canadian Food Inspection Agency, “Henneguya salminicola is found in southern B.C. also and in all species of salmon. I have previously examined smoked chum salmon sides that were riddled with cysts and some sockeye runs in Barkley Sound (southern B.C., west coast of Vancouver Island) are noted for their high incidence of infestation.”^{[citation needed]}

Sea lice, particularly Lepeophtheirus salmonis and various Caligus species, including C. clemensi and C. rogercresseyi, can cause deadly infestations of both farm-grown and wild salmon.^[77]^[78] Sea lice are ectoparasites which feed on mucus, blood, and skin, and migrate and latch onto the skin of wild salmon during free-swimming, planktonic nauplii and copepodid larval stages, which can persist for several days.^[79]^[80]^[81]

Large numbers of highly populated, open-net salmon farms^[A] can create exceptionally large concentrations of sea lice; when exposed in river estuaries containing large numbers of open-net farms, many young wild salmon are infected, and do not survive as a result.^[83]^[84] Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable. On the Pacific coast of Canada, the louse-induced mortality of pink salmon in some regions is commonly over 80%.^[85]

Effect of pile driving

The risk of injury caused by underwater pile driving has been studied by Dr. Halvorsen and her co-workers.^[86] The study concluded that the fish are at risk of injury if the cumulative sound exposure level exceeds 210 dB relative to 1 μPa² s.^{[clarification needed]}

Wild fisheries

Commercial

As can be seen from the production chart at the left, the global capture reported by different countries to the FAO of commercial wild salmon has remained fairly steady since 1990 at about one million tonnes per year. This is in contrast to farmed salmon (below) which has increased in the same period from about 0.6 million tonnes to well over two million tonnes.^[44]

Nearly all captured wild salmon are Pacific salmon. The capture of wild Atlantic salmon has always been relatively small, and has declined steadily since 1990. In 2011 only 2,500 tonnes were reported.^[12] In contrast, about half of all farmed salmon are Atlantic salmon.

Recreational

Recreational salmon fishing can be a technically demanding kind of sport fishing, not necessarily intuitive for beginning fishermen.^[87] A conflict exists between commercial fishermen and recreational fishermen for the right to salmon stock resources. Commercial fishing in estuaries and coastal areas is often restricted so enough salmon can return to their natal rivers where they can spawn and be available for sport fishing. On parts of the North American West Coast salmon sport fishing has completely replaced inshore commercial salmon fishing.^[88] In most cases, the commercial value of a salmon sold as seafood can be several times less than the value attributed to the same fish caught by a sport fisherman. This is “a powerful economic argument for allocating stock resources preferentially to sport fishing”.^[88]

Farms

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Main article: Aquaculture of salmon

Salmon aquaculture is a major contributor to the world production of farmed finfish, representing about US$10 billion annually. Other commonly cultured fish species include tilapia, catfish, sea bass, carp and bream. Salmon farming is significant in Chile, Norway, Scotland, Canada and the Faroe Islands; it is the source for most salmon consumed in the United States and Europe. Atlantic salmon are also, in very small volumes, farmed in Russia and Tasmania, Australia.

Salmon are carnivorous, and need to be fed meals produced from catching other wild forage fish and other marine organisms. Salmon farming leads to a high demand for wild forage fish. As a predator, salmon require large nutritional intakes of protein, and farmed salmon consume more fish than they generate as a final product. On a dry weight basis, 2–4 kg of wild-caught fish are needed to produce one kilogram of salmon.^[89] As the salmon farming industry expands, it requires more forage fish for feed, at a time when 75% of the world’s monitored fisheries are already near to or have exceeded their maximum sustainable yield.^[90] The industrial-scale extraction of wild forage fish for salmon farming affects the survivability of other wild predatory fish which rely on them for food. Research is ongoing into sustainable and plant-based salmon feeds.^[91]

Intensive salmon farming uses open-net cages, which have low production costs. It has the drawback of allowing disease and sea lice to spread to local wild salmon stocks.^[92]

Another form of salmon production, which is safer but less controllable, is to raise salmon in hatcheries until they are old enough to become independent. They are released into rivers in an attempt to increase the salmon population. This system is referred to as ranching. It was very common in countries such as Sweden, before the Norwegians developed salmon farming, but is seldom done by private companies. As anyone may catch the salmon when they return to spawn, a company is limited in benefiting financially from their investment.

Because of this, the ranching method has mainly been used by various public authorities and non-profit groups, such as the Cook Inlet Aquaculture Association, as a way to increase salmon populations in situations where they have declined due to overharvesting, construction of dams and habitat destruction or fragmentation. Negative consequences to this sort of population manipulation include genetic “dilution” of the wild stocks. Many jurisdictions are now beginning to discourage supplemental fish planting in favour of harvest controls, and habitat improvement and protection.

A variant method of fish stocking, called ocean ranching, is under development in Alaska. There, the young salmon are released into the ocean far from any wild salmon streams. When it is time for them to spawn, they return to where they were released, where fishermen can catch them.

An alternative method to hatcheries is to use spawning channels. These are artificial streams, usually parallel to an existing stream, with concrete or rip-rap sides and gravel bottoms. Water from the adjacent stream is piped into the top of the channel, sometimes via a header pond, to settle out sediment. Spawning success is often much better in channels than in adjacent streams due to the control of floods, which in some years can wash out the natural redds. Because of the lack of floods, spawning channels must sometimes be cleaned out to remove accumulated sediment. The same floods that destroy natural redds also clean the regular streams. Spawning channels preserve the natural selection of natural streams, as there is no benefit, as in hatcheries, to use prophylactic chemicals to control diseases.^{[citation needed]}

Farm-raised salmon are fed the carotenoids astaxanthin and canthaxanthin to match their flesh colour to wild salmon^[93] to improve their marketability.^[94] Wild salmon get these carotenoids, primarily astaxanthin, from eating shellfish and krill.

One proposed alternative to the use of wild-caught fish as feed for the salmon, is the use of soy-based products. This should be better for the local environment of the fish farm, but producing soy beans has a high environmental cost for the producing region. The fish omega-3 fatty acid content would be reduced compared to fish-fed salmon.

Another possible alternative is a yeast-based coproduct of bioethanol production, proteinaceous fermentation biomass. Substituting such products for engineered feed can result in equal (sometimes enhanced) growth in fish.^[95] With its increasing availability, this would address the problems of rising costs for buying hatchery fish feed.

Yet another attractive alternative is the increased use of seaweed. Seaweed provides essential minerals and vitamins for growing organisms. It offers the advantage of providing natural amounts of dietary fiber and having a lower glycemic load than grain-based fish meal.^[95] In the best-case scenario, widespread use of seaweed could yield a future in aquaculture that eliminates the need for land, freshwater, or fertilizer to raise fish.^[96]^{[failed verification]}

Management

Main article: Environmental issues with salmon

Salmon population levels are of concern in the Atlantic and in some parts of the Pacific.^[98] The population of wild salmon declined markedly in recent decades, especially North Atlantic populations, which spawn in the waters of western Europe and eastern Canada, and wild salmon in the Snake and Columbia River systems in northwestern United States.

Alaska fishery stocks are still abundant, and catches have been on the rise in recent decades, after the state initiated limitations in 1972.^[99]^[100]^{[citation needed]} Some of the most important Alaskan salmon sustainable wild fisheries are located near the Kenai River, Copper River, and in Bristol Bay. Fish farming of Pacific salmon is outlawed in the United States Exclusive Economic Zone,^[101] however, there is a substantial network of publicly funded hatcheries,^[102] and the State of Alaska’s fisheries management system is viewed as a leader in the management of wild fish stocks.

In Canada, returning Skeena River wild salmon support commercial, subsistence and recreational fisheries, as well as the area’s diverse wildlife on the coast and around communities hundreds of miles inland in the watershed. The status of wild salmon in Washington is mixed. Of 435 wild stocks of salmon and steelhead, only 187 of them were classified as healthy; 113 had an unknown status, one was extinct, 12 were in critical condition and 122 were experiencing depressed populations.^[103]

The commercial salmon fisheries in California have been either severely curtailed or closed completely in recent years, due to critically low returns on the Klamath and or Sacramento rivers, causing millions of dollars in losses to commercial fishermen.^[104] Both Atlantic and Pacific salmon are popular sportfish.

Salmon populations have been established in all the Great Lakes. Coho stocks were planted by the state of Michigan in the late 1960s to control the growing population of non-native alewife. Now Chinook (king), Atlantic, and coho (silver) salmon are annually stocked in all Great Lakes by most bordering states and provinces. These populations are not self-sustaining and do not provide much in the way of a commercial fishery, but have led to the development of a thriving sport fishery.

Wild, self sustaining Pacific salmon populations have been established in New Zealand, Chile, and Argentina.^[105] They are highly prized by sport fishers, but others worry about displacing native fish species.^[106] Also, and especially in Chile (Aquaculture in Chile), both Atlantic and Pacific salmon are used in net pen farming.

In 2020 researchers reported widespread declines in the sizes of four species of wild Pacific salmon: Chinook, chum, coho, and sockeye. These declines have been occurring for 30 years, and are thought to be associated with climate change and competition with growing numbers of pink and hatchery salmon.^[107]^[97]

As food

Main article: Salmon as food

Salmon is a popular food fish. Classified as an oily fish,^[108] salmon is considered to be healthy due to the fish’s high protein, high omega-3 fatty acids, and high vitamin D^[109] content. Salmon is also a source of cholesterol, with a range of 23–214 mg/100 g depending on the species.^[110] According to reports in the journal Science, farmed salmon may contain high levels of dioxins.^{[medical citation needed]} PCB (polychlorinated biphenyl) levels may be up to eight times higher in farmed salmon than in wild salmon,^[111] but still well below levels considered dangerous.^[112]^[113] Nonetheless, according to a 2006 study published in the Journal of the American Medical Association, the benefits of eating even farmed salmon still outweigh any risks imposed by contaminants.^[114] Farmed salmon has a high omega-3 fatty acid content comparable to wild salmon.^[115] The type of omega-3 present may not be a factor for other important health functions.^[vague]

Salmon flesh is generally orange to red, although white-fleshed wild salmon with white-black skin colour occurs. The natural colour of salmon results from carotenoid pigments, largely astaxanthin, but also canthaxanthin, in the flesh.^[116] Wild salmon get these carotenoids from eating krill and other tiny shellfish.

The vast majority of Atlantic salmon available in market around the world are farmed (almost 99%),^[117] whereas the majority of Pacific salmon are wild-caught (greater than 80%). Canned salmon in the U.S. is usually wild Pacific catch, though some farmed salmon is available in canned form. Smoked salmon is another popular preparation method, and can either be hot or cold smoked. Lox can refer to either cold-smoked salmon or salmon cured in a brine solution (also called gravlax). Traditional canned salmon includes some skin (which is harmless) and bone (which adds calcium). Skinless and boneless canned salmon is also available.

Raw salmon flesh may contain Anisakis nematodes, marine parasites that cause anisakiasis. Before the availability of refrigeration, the Japanese did not consume raw salmon. Salmon and salmon roe have only recently come into use in making sashimi (raw fish) and sushi.^[118]

To the Indigenous peoples of the Pacific Northwest Coast, salmon is considered a vital part of the diet. Specifically, the indigenous peoples of Haida Gwaii, located near former Queen Charlotte Island in British Columbia, rely on salmon as one of their main sources of food, although many other bands have fished Pacific waters for centuries.^[119] Salmon are not only ancient and unique, but it is important because it is expressed in culture, art forms, and ceremonial feasts. Annually, salmon spawn in Haida, feeding on everything on the way upstream and down.^[119] Within the Haida nation, salmon is referred to as “tsiin”,^[119] and is prepared in several ways including smoking, baking, frying, and making soup.

Historically, there has always been enough salmon, as traditional subsistence fishing methods did not result in overfishing, and people only took what they needed.^[120] In 2003, a report on First Nations participation in commercial fisheries, including salmon, commissioned by BC’s Ministry of Agriculture and Food found that there were 595 First Nation-owned and operated commercial vessels in the province. Of those vessels, First Nations’ members owned 564.^[120] However, employment within the industry has decreased overall by 50% in the last decade, with 8,142 registered commercial fishermen in 2003. This has affected employment for many fisherman, who rely on salmon as a source of income.^[relevant?]

Black bears also rely on salmon as food. The leftovers the bears leave behind are considered important nutrients for the Canadian forest, such as the soil, trees and plants. In this sense, the salmon feed the forest and in return receive clean water and gravel in which to hatch and grow, sheltered from extremes of temperature and water flow in times of high and low rainfall.^[119] However, the condition of the salmon in Haida has been affected in recent decades. Due to logging and development, much of the salmon’s habitat (i.e., Ain River) has been destroyed, resulting in the fish being close to endangered.^[119] For residents, this has resulted in limits on catches, in turn, has affected families diets, and cultural events such as feasts. Some of the salmon systems in danger include: the Davidon, Naden, Mamim, and Mathers.^[119]

Fishing

History

Commercial fishing

Recreational fishing

Mythology

The salmon is an important creature in several strands of Celtic mythology and poetry, which often associated them with wisdom and venerability. In Irish folklore, fishermen associated salmon with fairies and thought it was unlucky to refer to them by name.^[130] In Irish mythology, a creature called the Salmon of Knowledge^[131] plays key role in the tale The Boyhood Deeds of Fionn. In the tale, the Salmon will grant powers of knowledge to whoever eats it, and is sought by poet Finn Eces for seven years. Finally Finn Eces catches the fish and gives it to his young pupil, Fionn mac Cumhaill, to prepare it for him. However, Fionn burns his thumb on the salmon’s juices, and he instinctively puts it in his mouth. In so doing, he inadvertently gains the Salmon’s wisdom. Elsewhere in Irish mythology, the salmon is also one of the incarnations of both Tuan mac Cairill^[132] and Fintan mac Bóchra.^[133]

Salmon also feature in Welsh mythology. In the prose tale Culhwch and Olwen, the Salmon of Llyn Llyw is the oldest animal in Britain, and the only creature who knows the location of Mabon ap Modron. After speaking to a string of other ancient animals who do not know his whereabouts, King Arthur‘s men Cai and Bedwyr are led to the Salmon of Llyn Llyw, who lets them ride its back to the walls of Mabon’s prison in Gloucester.^[134]

In Norse mythology, after Loki tricked the blind god Höðr into killing his brother Baldr, Loki jumped into a river and transformed himself into a salmon to escape punishment from the other gods. When they held out a net to trap him he attempted to leap over it but was caught by Thor who grabbed him by the tail with his hand, and this is why the salmon’s tail is tapered.^[135]

Salmon are central spiritually and culturally to Native American mythology on the Pacific coast, from the Haida and Coast Salish peoples, to the Nuu-chah-nulth peoples in British Columbia.

March 20, 2025

Siberian Tiger
The Siberian Tiger or Amur tiger is a population of the tiger subspecies Panthera tigris tigris native to Northeast China, the Russian Far East,^[1] and possibly North Korea.^[2] It once ranged throughout the Korean Peninsula, but currently inhabits mainly the Sikhote-Alin mountain region in south-west Primorye Province in the Russian Far East. In 2005, there were 331–393 adult and subadult Siberian tigers in this region, with a breeding adult population of about 250 individuals. The population had been stable for more than a decade because of intensive conservation efforts, but partial surveys conducted after 2005 indicate that the Russian tiger population was declining.^[3] An initial census held in 2015 indicated that the Siberian tiger population had increased to 480–540 individuals in the Russian Far East, including 100 cubs.^[4]^[5] This was followed up by a more detailed census which revealed there was a total population of 562 wild Siberian tigers in Russia.^[6] As of 2014, about 35 individuals were estimated to range in the international border area between Russia and China.^[7] As of 2022, about 756 Siberian tigers including 200 cubs were estimated to inhabit the Russian Far East.^[8]

The Siberian tiger is genetically close to the now-extinct Caspian tiger. Results of a phylogeographic study comparing mitochondrial DNA from Caspian tigers and living tiger populations indicate that the common ancestor of the Siberian and Caspian tigers colonized Central Asia from eastern China, via the Gansu−Silk Road corridor, and then subsequently traversed Siberia eastward to establish the Siberian tiger population in the Russian Far East.^[9] The Caspian and Siberian tiger populations were the northernmost in mainland Asia.^[10]^[11]

The Siberian tiger was also called “Amur tiger”, “Manchurian tiger”, “Korean tiger”,^[2] and “Ussurian tiger”, depending on the region where individuals were observed.^[10]^[12]

Taxonomy

Siberian tiger face

Felis tigris was the scientific name proposed by Carl Linnaeus in 1758 for the tiger.^[13] In the 19th century, several tiger specimens were collected in East Asia and described:
- Felis tigris altaicus proposed by Coenraad Jacob Temminck in 1844 were tiger skins with long hairs and dense coats sold in Japan, which originated in Korea, most likely from animals killed in the Altai and Pisihan Mountains.^[14]
- Tigris longipilis proposed by Leopold Fitzinger in 1868 was based on a long-haired tiger skin in the Natural History Museum, Vienna.^[15]
- Felis tigris var. amurensis proposed by Charles Dode in 1871 was based on tiger skins from the Amur region.^[16]
- Felis tigris coreensis by Emil Brass in 1904 was a tiger skin from Korea.^[17]
The validity of several tiger subspecies was questioned in 1999. Most putative subspecies described in the 19th and 20th centuries were distinguished on the basis of fur length and colouration, striping patterns and body size – characteristics that vary widely within populations. Morphologically, tigers from different regions vary little, and gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two tiger subspecies as valid, namely Panthera tigris tigris in mainland Asia, and P. t. sondaica in the Greater Sunda Islands and possibly in Sundaland.^[18]^[19] In 2015, morphological, ecological and molecular traits of all putative tiger subspecies were analysed in a combined approach. Results support distinction of the two evolutionary groups: continental and Sunda tigers. The authors proposed recognition of only two subspecies: namely P. t. tigris comprising the Bengal, Malayan, Indochinese, South China, Siberian and Caspian tiger populations; and P. t. sondaica comprising the Javan, Bali and Sumatran tiger populations.^[20]

In 2017, the Cat Specialist Group revised felid taxonomy and now recognizes all the tiger populations in mainland Asia as P. t. tigris.^[1]

Phylogeny

Phylogenetic relationship of tiger populations^[9] Note the close relationship between the Caspian (PTV or P. t. virgata) and Siberian (ALT or P. t. altaica) tigers.

Several reports have been published since the 1990s on the genetic makeup of the Siberian tiger and its relationship to other populations. One of the most important outcomes has been the discovery of low genetic variability in the wild population, especially when it comes to maternal or mitochondrial DNA lineages.^[21] It seems that a single mtDNA haplotype almost completely dominates the maternal lineages of wild Siberian tigers. On the other hand, captive tigers appear to show higher mtDNA diversity. This may suggest that the subspecies has experienced a very recent genetic bottleneck caused by human pressure, with the founders of the captive population having been captured when genetic variability was higher in the wild.^[22]^[23]

At the start of the 21st century, researchers from the University of Oxford, U.S. National Cancer Institute and Hebrew University of Jerusalem collected tissue samples from 20 of 23 Caspian tiger specimens kept in museums across Eurasia. They sequenced at least one segment of five mitochondrial genes and found a low amount of variability of the mitochondrial DNA in Caspian tigers as compared to other tiger subspecies. They re-assessed the phylogenetic relationships of tiger subspecies and observed a remarkable similarity between Caspian and Siberian tigers, indicating that the Siberian tiger is the genetically closest living relative of the Caspian tiger, which strongly implies a very recent common ancestry. Based on phylogeographic analysis, they suggested that the ancestor of Caspian and Siberian tigers colonized Central Asia less than 10,000 years ago via the Gansu−Silk Road region from eastern China, and subsequently traversed eastward to establish the Siberian tiger population in the Russian Far East. The events of the Industrial Revolution may have been the critical factor in the reciprocal isolation of Caspian and Siberian tigers from what was likely a single contiguous population.^[9]

Samples of 95 wild Amur tigers were collected throughout their native range to investigate questions relative to population genetic structure and demographic history. Additionally, targeted individuals from the North American ex situ population were sampled to assess the genetic representation found in captivity. Population genetic and Bayesian structure analyses clearly identified two populations separated by a development corridor in Russia. Despite their well-documented 20th century decline, the researchers failed to find evidence of a recent population bottleneck, although genetic signatures of a historical contraction were detected. This disparity in signal may be due to several reasons, including historical paucity in population genetic variation associated with postglacial colonisation and potential gene flow from an extirpated Chinese population. The extent and distribution of genetic variation in captive and wild populations were similar, yet gene variants persisted ex situ that were lost in situ. Overall, their results indicate the need to secure ecological connectivity between the two Russian populations to minimize loss of genetic diversity and overall susceptibility to stochastic events, and support a previous study suggesting that the captive population may be a reservoir of gene variants lost in situ.^[24]

In 2013, the whole genome of the Siberian tiger was sequenced and published.^[25] Tigers in mainland Asia fall into two clades: the northern clade comprises the Siberian and Caspian tiger populations, and the southern clade all remaining continental tiger populations.^[20] A study published in 2018 was based on 32 tiger specimens using a whole-genome sequencing for analysis. Results support six monophyletic tiger clades and indicate that the most recent common ancestor lived about 110,000 years ago.^[26]

Characteristics

Captive Siberian tiger at Münster Zoo

The tiger is reddish-rusty, or rusty-yellow in colour, with narrow black transverse stripes. The body length is not less than 150 cm (59 in), condylobasal length of skull 250 mm (9.8 in), zygomatic width 180 mm (7.1 in), and length of upper carnassial tooth over 26 mm (1.0 in) long. It has an extended supple body standing on rather short legs with a fairly long tail.^[11]

Body size

In the 1980s, the typical weight range of wild Siberian tigers was indicated as 180 to 306 kg (397 to 675 lb) for males and 100 to 167 kg (220 to 368 lb) for females.^[10] Exceptionally large individuals were targeted and shot by hunters.^[27]

In 2005, a group of Russian, American and Indian zoologists published an analysis of historical and contemporary data on body weights of wild and captive tigers, both female and male across all subspecies. The data used include weights of tigers that were older than 35 months and measured in the presence of authors. Their comparison with historical data indicates that up to the first half of the 20th century both male and female Siberian tigers were on average heavier than post-1970 ones. The average historical wild male Siberian tiger weighed 215.3 kg (475 lb) and the female 137.5 kg (303 lb); the contemporary wild male Siberian tiger weighs 176.4 kg (389 lb) on average with an asymptotic limit being 222.3 kg (490 lb); a wild female weighs 117.9 kg (260 lb) on average. Historical Siberian tigers and Bengal tigers were the largest ones, whereas contemporary Siberian tigers are on average lighter than Bengal tigers. The reduction of the body weight of today’s Siberian tigers may be explained by concurrent causes, namely the reduced abundance of prey because of illegal hunting and that the individuals were usually sick or injured and captured in a conflict situation with people.^[28]

Measurements taken by scientists of the Siberian Tiger Project in the Sikhote-Alin range from 178 to 208 cm (70 to 82 in) in head and body length measured in straight line, with an average of 195 cm (77 in) for males; and for females ranging from 167 to 182 cm (66 to 72 in) with an average of 174 cm (69 in). The average tail measures 99 cm (39 in) in males and 91 cm (36 in) in females. The longest male measured 309 cm (122 in) in total length including a tail of 101 cm (40 in) and with a chest girth of 127 cm (50 in). The longest female measured 270 cm (110 in) in total length including tail of 88 cm (35 in) and with a chest girth of 108 cm (43 in).^[29] A male captured by members of the Siberian Tiger Project weighed 206 kg (454 lb), and the largest radio-collared male weighed 212 kg (467 lb).^[30]^[31]

The Siberian tiger is often considered to be the largest tiger.^[32] A wild male, killed in Manchuria by the Sungari River in 1943, reportedly measured 350 cm (140 in) “over the curves”, with a tail length of about 1 m (3 ft 3 in). It weighed about 300 kg (660 lb). Dubious sources mention weights of 318 and 384 kg (701 and 847 lb) and even 408 kg (899 lb).^[33]

In 2019, one of the largest Siberian tiger was recorded that was thought to weigh 384.09 kg (846.8 lb) and measure over 3.4 m (11 ft) from nose to tail.^[34]

Skull

The skull of the Siberian tiger is characterized by its large size. The facial region is very powerful and very broad in the region of the canines.^[11] The skull prominences, especially in the sagittal crest and crista occipitalis, are very high and strong in old males, and often much more massive than usually observed in the biggest skulls of Bengal tigers. The size variation in skulls of Siberian tigers ranges from 331 to 383 mm (13.0 to 15.1 in) in nine individuals measured. A female skull is always smaller and never as heavily built and robust as that of a male. The height of the sagittal crest in its middle part reaches as much as 27 mm (1.1 in), and in its posterior part up to 46 mm (1.8 in).^[35]

Female skulls range from 279.7 to 310.2 mm (11.01 to 12.21 in). The skulls of male Caspian tigers from Turkestan had a maximum length of 297.0 to 365.8 mm (11.69 to 14.40 in), while that of females measured 195.7 to 255.5 mm (7.70 to 10.06 in). A tiger killed on the Sumbar River in Kopet Dag in January 1954 had a greatest skull length of 385 mm (15.2 in), which is considerably more than the known maximum for this population and slightly exceeds that of most Siberian tigers. However, its condylobasal length was only 305 mm (12.0 in), smaller than those of the Siberian tigers, with a maximum recorded condylobasal length of 342 mm (13.5 in).^[29] The biggest skull of a Siberian tiger from northeast China measured 406 mm (16.0 in) in length, which is about 20–30 mm (0.79–1.18 in) more than the maximum skull lengths of tigers from the Amur region and northern India,^[12] with the exception of a skull of a northern Indian tiger from the vicinity of Nagina, which measured 413 mm (16.25 in) “over the bone”.^[36]

Fur and coat

A Siberian tiger cub at the Pittsburgh Zoo

The ground colour of Siberian tigers’ pelage is often very pale, especially in winter coat. However, variations within populations may be considerable. Individual variation is also found in form, length, and partly in colour, of the dark stripes, which have been described as being dark brown rather than black.^[35]

The fur of the Siberian tiger is moderately thick, coarse and sparse compared to that of other felids living in the former Soviet Union. Compared to the extinct westernmost populations, the Siberian tiger’s summer and winter coats contrast sharply with other subspecies. Generally, the coat of western populations was brighter and more uniform than that of the Far Eastern populations. The summer coat is coarse, while the winter coat is denser, longer, softer, and silkier. The winter fur often appears quite shaggy on the trunk and is markedly longer on the head, almost covering the ears. Siberian and Caspian tigers had the thickest fur amongst tigers.^[11]^[10]

The whiskers and hair on the back of the head and the top of the neck are also greatly elongated. The background colour of the winter coat is generally less bright and rusty compared to that of the summer coat. Because of the winter fur’s greater length, the stripes appear broader with less defined outlines. The summer fur on the back is 15–17 mm (0.59–0.67 in) long, 30–50 mm (1.2–2.0 in) along the top of the neck, 25–35 mm (0.98–1.38 in) on the abdomen, and 14–16 mm (0.55–0.63 in) on the tail. The winter fur on the back is 40–50 mm (1.6–2.0 in), 70–110 mm (2.8–4.3 in) on the top of the neck, 70–95 mm (2.8–3.7 in) on the throat, 60–100 mm (2.4–3.9 in) on the chest and 65–105 mm (2.6–4.1 in) on the abdomen. The whiskers are 90–115 mm (3.5–4.5 in).^[11]

Distribution and habitat

Sikhote-Alin in Primorsky Krai

A tiger in Bastak Nature Reserve

The Siberian tiger once inhabited much of the Korean Peninsula, Manchuria and other parts of north-eastern China, the eastern part of Siberia and the Russian Far East, perhaps as far west as Mongolia and the area of Lake Baikal, where the Caspian tiger also reportedly occurred.^[11] During the late Pleistocene and Holocene, it was likely connected to the South China tiger population through corridors in the Yellow River basin, before humans interrupted gene flow.^[37]

Today, its range stretches south to north for almost 1,000 km (620 mi) the length of Primorsky Krai and into southern Khabarovsk Krai east and south of the Amur River. It also occurs within the Greater Xing’an Range, which crosses into Russia from China at several places in southwest Primorye. This region represents a merger zone of the East Asian temperate broadleaf and mixed forest and the taiga, resulting in a mosaic of forest types that vary in elevation and topography. Key habitats of the Siberian tiger are Korean pine forests with a complex composition and structure.^[38]

The faunal complex of the region is represented by a mixture of Asian and boreal life forms. The ungulate complex is represented by seven species, with Manchurian wapiti, Siberian roe deer, and wild boar being the most common throughout the Sikhote-Alin mountains but rare in higher altitude spruce-fir forests. Sika deer are restricted to the southern half of the Sikhote-Alin mountains. Siberian musk deer and Amur moose are associated with the conifer forests and are near the southern limits of their distribution in the central Sikhote-Alin mountains.^[39]

In 2005, the number of Amur tigers in China was estimated at 18–22, and 331–393 in the Russian Far East, comprising a breeding adult population of about 250, fewer than 100 likely to be sub-adults, more than 20 likely to be less than 3 years of age. More than 90% of the population occurred in the Sikhote Alin mountain region.^[3] An unknown number of tigers survive in the reserve areas around Baekdu Mountain, on the border between China and North Korea, based on tracks and sightings.^[2]

In August 2012, a Siberian tiger with four cubs was recorded for the first time in northeastern China’s Hunchun National Nature Reserve located in the vicinity of the international borders with Russia and North Korea.^[40]^[41] Camera-trap surveys carried out in the spring seasons of 2013 and 2014 revealed between 27 and 34 tigers along the China-Russian border.^[7] In April 2014, World Wide Fund for Nature personnel captured a video of a tigress with cubs in inland China.^[42] The tiger population in the Changbai Mountains dispersed westwards between 2003 and 2016.^[43] Camera trap surveys between 2013 and 2018 revealed about 55 Siberian tigers in four forested landscapes in northeastern China: Laoyeling, Zhangguangcai Range, Wandashan and Lesser Khingan Mountains. Feces, urine and hair was used to genetically identify 30 tigers in this region. However, only Laoyeling is thought to support a breeding population.^[44]

Ecology and behavior

A Siberian tiger photographed by a camera trap

Siberian tigers are known to travel up to 1,000 km (620 mi) over ecologically unbroken country.^[11] In 1992 and 1993, the maximum total population density of the Sikhote-Alin tiger population was estimated at 0.62 tigers in 100 km² (39 sq mi). The maximum adult population estimated in 1993 reached 0.3 tigers in 100 km² (39 sq mi), with a sex ratio of averaging 2.4 females per male. These density values were much lower than what had been reported for other subspecies at the time.^[45] In 2004, dramatic changes in land tenure, population density, and reproductive output in the core area of the Sikhote-Alin Zapovednik Siberian Tiger Project were detected, suggesting that when tigers are well protected from human-induced mortality for long periods, the adult female population density increases significantly. When more adult females survived, the mothers shared their home ranges with their daughters once the daughters reached maturity. By 2007, population density of tigers was estimated at 0.8±0.4 tigers in 100 km² (39 sq mi) in the southern part of Sikhote-Alin Zapovednik, and 0.6±0.3 tigers in 100 km² (39 sq mi) in the central part of the protected area.^[46]

Siberian tigers share habitat with Amur leopards (P. pardus orientalis), but in the Changbai Mountains have been recorded more often in lower elevations than leopards.^[47]

Hunting and diet

A diorama at the Museo Civico di Storia Naturale di Milano shows a tiger chasing a sika deer

Prey species of the tiger include ungulates such as Manchurian wapiti (Cervus canadensis xanthopygus), Siberian musk deer (Moschus moschiferus), long-tailed goral (Naemorhedus caudatus), moose (Alces alces), Siberian roe deer (Capreolus pygargus) and sika deer (Cervus nippon), wild boar (Sus scrofa), and even sometimes small size Asiatic black bears (Ursus thibetanus) and brown bears (Ursus arctos). Siberian tigers also take smaller prey like hares, rabbits, pikas and even salmon.^[33]^[38] Scat was collected along the international border between Russia and China between November 2014 and April 2015; 115 scat samples of nine tigers contained foremost remains of wild boar, sika deer and roe deer.^[48]

Between January 1992 and November 1994, 11 tigers were captured, fitted with radio-collars and monitored for more than 15 months in the eastern slopes of the Sikhote-Alin mountain range. Results of this study indicate that their distribution is closely associated with distribution of Manchurian wapiti, while distribution of wild boar was not such a strong predictor for tiger distribution. Although they prey on both Siberian roe deer and sika deer, overlap of these ungulates with tigers was low. Distribution of moose was poorly associated with tiger distribution. The distribution of preferred habitat of key prey species was an accurate predictor of tiger distribution.^[38]

Results of a three-year study on Siberian tigers indicate that the mean interval between their kills and estimated prey consumption varied across seasons: during 2009 to 2012, three adult tigers killed prey every 7.4 days in summer and consumed a daily average of 7.89 kg (17.4 lb); in winter they killed more large-bodied prey, made kills every 5.7 days and consumed a daily average of 10.3 kg (23 lb).^[49]

Interspecific predatory relationships

Siberian tiger. Frame from a camera trap

Taxidermy exhibit portraying a tiger fighting a brown bear, Vladivostok Museum

Following a decrease of ungulate populations from 1944 to 1959, 32 cases of Amur tigers attacking both Ussuri brown (Ursus arctos lasiotus) and Ussuri black bears (U. thibetanus ussuricus) were recorded in the Russian Far East, and hair of bears were found in several tiger scat samples. Tigers attack black bears less often than brown bears, as the latter live in more open habitats and are not able to climb trees. In the same time period, four cases of brown bears killing female tigers and young cubs were reported, both in disputes over prey and in self-defense. Tigers mainly feed on the bear’s fat deposits, such as the back, hams and groin.^[11]

When Amur tigers prey on brown bears, they usually target young and sub-adult bears, besides small female adults taken outside their dens, generally when lethargic from hibernation.^[27] Predation by tigers on denned brown bears was not detected during a study carried between 1993 and 2002.^[50] Ussuri brown bears, along with the smaller black bears constitute 2.1% of the Siberian tiger’s annual diet, of which 1.4% are brown bears.^[51]^[52]

The effect the presence of tigers has on brown bear behavior seems to vary. In the winters of 1970–1973, Yudakov and Nikolaev recorded two cases of bears showing no fear of tigers and another case of a brown bear changing path upon crossing tiger tracks.^[53] Other researchers have observed bears following tiger tracks to scavenge tiger kills and to potentially prey on tigers.^[11]^[51] Despite the threat of predation, some brown bears actually benefit from the presence of tigers by appropriating tiger kills that the bears may not be able to successfully hunt themselves.^[51] Brown bears generally prefer to contest the much smaller female tigers.^[54] During telemetry research in the Sikhote-Alin Nature Reserve, 44 direct confrontations between bears and tigers were observed, in which bears in general were killed in 22 cases, and tigers in 12 cases.^[55] There are reports of brown bears specifically targeting Amur leopards and tigers to abstract their prey. In the Sikhote-Alin reserve, 35% of tiger kills were stolen by bears, with tigers either departing entirely or leaving part of the kill for the bear.^[56] Some studies show that bears frequently track down tigers to usurp their kills, with occasional fatal outcomes for the tiger. A report from 1973 describes twelve known cases of brown bears killing tigers, including adult males; in all cases the tigers were subsequently eaten by the bears.^[57]^[58]

The relationship between the Amur tiger and the Himalayan bear is not specifically studied. Numerous publications on these species there are mainly episodic and survey data on this issue are collected by different authors in selected areas which do not give a complete picture of the nature.^[51]

Tigers depress wolf (Canis lupus) numbers, either to the point of localized extinction or to such low numbers as to make them a functionally insignificant component of the ecosystem. Wolves appear capable of escaping competitive exclusion from tigers only when human pressure decreases tiger numbers. In areas where wolves and tigers share ranges, the two species typically display a great deal of dietary overlap, resulting in intense competition. Wolf and tiger interactions are well documented in Sikhote-Alin, where until the beginning of the 20th century, very few wolves were sighted. Wolf numbers may have increased in the region after tigers were largely eliminated during the Russian colonisation in the late 19th century and early 20th century. This is corroborated by native inhabitants of the region claiming that they had no memory of wolves inhabiting Sikhote-Alin until the 1930s, when tiger numbers decreased. Today, wolves are considered scarce in tiger habitat, being found in scattered pockets, and usually seen travelling as loners or in small groups. First hand accounts on interactions between the two species indicate that tigers occasionally chase wolves from their kills, while wolves will scavenge from tiger kills. Tigers are not known to prey on wolves, though there are four records of tigers killing wolves without consuming them.^[59] Tigers recently released are also said to hunt wolves.^[60]

This competitive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters in the Far East to tolerate the big cats, as they limit ungulate populations less than wolves, and are effective in controlling wolf numbers.^[61]

Siberian tigers also compete with the Eurasian lynx (Lynx lynx) and occasionally kill and eat them. Eurasian lynx remains have been found in the stomach contents of Siberian tigers in Russia.^[11] In March 2014, a dead lynx discovered in Bastak Nature Reserve bore evidence of predation by a Siberian tiger. The tiger apparently ambushed, pursued, and killed the lynx but only consumed it partially. This incident marks one of the first documented cases of a tiger preying on a lynx, and indicates that the tiger might have been more intent on eliminating a competitor than on catching prey.^[62]

Reproduction and life cycle

A tiger at the Rehabilitation and Reintroduction Center for Amur (Siberian) Tigers in the village of Alekseevka, Primorsky Krai, Russia

Three orphaned Siberian tigers rescued after their mothers were killed by poachers are released back to the wild in Russia

Siberian tigers mate at any time of the year. A female signals her receptiveness by leaving urine deposits and scratch marks on trees. She will spend 5 or 6 days with the male, during which she is receptive for three days. Gestation lasts from 3 to 3½ months. Litter size is normally two or four cubs but there can be as many as six. The cubs are born blind in a sheltered den and are left alone when the female leaves to hunt for food. Cubs are divided equally between sexes at birth. However, by adulthood there are usually two to four females for every male. The female cubs remain with their mothers longer, and later they establish territories close to their original ranges. Males, on the other hand, travel unaccompanied and range farther earlier in their lives, making them more vulnerable to poachers and other tigers.^[63] A Siberian tiger family comprising an adult male, a female and three cubs were recorded in 2015.^[64]

At 35 months of age, tigers are sub-adults. Males reach sexual maturity at the age of 48 to 60 months.^[65]^[66]

The average lifespan for Siberian tigers ranges from 16–18 years. Wild individuals tend to live between 10–15 years, while in captivity individuals may live up to 25 years.^[67]^[68]

Threats

Results of genetic analysis of 95 wild Siberian tiger samples from Russia revealed that genetic diversity is low, only 27–35 individuals contributed to their genes. Further exacerbating the problem is that more than 90% of the population occurred in the Sikhote Alin mountain region. Tigers rarely move across the development corridor, which separates this sub-population from the much smaller sub-population in southwest Primorye province.^[24]

The winter of 2006–2007 was marked by heavy poaching.^[46] Poaching of tigers and their wild prey species is considered to be driving the decline, although heavy snows in the winter of 2009 could have biased the data.^[3] In northern China’s Huang Ni He National Nature Reserve, poachers set up foremost snare traps, but there is not sufficient personnel to patrol this 75 km² (29 sq mi) area throughout the year.^[69] In Hunchun National Nature Reserve, poaching of ungulate species impedes recovery of the tiger population.^[70]

In the past

After the dissolution of the Soviet Union, illegal deforestation and bribery of park rangers facilitated poaching of Siberian tigers. Local hunters had access to a formerly sealed off lucrative Chinese market, and this once again put the region’s tiger population at risk of extinction.^[63] While improvement in the local economy has led to greater resources being invested in conservation efforts, an increase in economic activity has led to an increased rate of development and deforestation. The major obstacle in preserving the tiger is the enormous territory individual tigers require; up to 450 km² (170 sq mi) is needed by a single female and more for a single male.^[71]

The Siberian tiger was once common in the Korean Peninsula.^[11] It was eradicated during the period of Korea under Japanese rule between 1910 and 1945.^[72]

Conservation

Tigers are included on CITES Appendix I, banning international trade. All tiger range states and countries with consumer markets have banned domestic trade as well.^[73] At the 14th Conference of the Parties to CITES in 2007, stronger enforcement measures were called for, as well as an end to tiger farming.^[74]

In 1992, the Siberian Tiger Project was founded, with the aim of providing a comprehensive picture of the ecology of the Amur tiger and the role of tigers in the Russian Far East through scientific studies. By capturing and outfitting tigers with radio collars, their social structure, land use patterns, food habits, reproduction, mortality patterns and their relation with other inhabitants of the ecosystem, including humans is studied. These data compilations will hopefully contribute toward minimizing poaching threats because of traditional hunting. The Siberian Tiger Project has been productive in increasing local capacity to address human-tiger conflict with a Tiger Response Team, part of the Russian government’s Inspection Tiger, which responds to all tiger-human conflicts; by continuing to enhance the large database on tiger ecology and conservation with the goal of creating a comprehensive Siberian tiger conservation plan; and training the next generation of Russian conservation biologists.^[75]

In August 2010, China and Russia agreed to enhance conservation and cooperation in protected areas in a transboundary area for Amur tigers. China has undertaken a series of public awareness campaigns including celebration of the first Global Tiger Day in July 2010, and International Forum on Tiger Conservation and Tiger Culture and China 2010 Hunchun Amur Tiger Culture Festival in August 2010.^[76]

Siberian Tiger at Yerevan Zoo, Armenia.

Reintroduction

Further information: Reintroduction, Species translocation, and Siberian Tiger Introduction Project

Inspired by findings that the Amur tiger is the closest relative of the Caspian tiger, there has been discussion whether the Amur tiger could be an appropriate subspecies for reintroduction into a safe place in Central Asia. The Amu-Darya Delta was suggested as a potential site for such a project. A feasibility study was initiated to investigate if the area is suitable and if such an initiative would receive support from relevant decision makers. A viable tiger population of about 100 animals would require at least 5,000 km² (1,900 sq mi) of large tracts of contiguous habitat with rich prey populations. Such habitat is not presently available in the delta and so cannot be provided in the short term. The proposed region is therefore unsuitable for the reintroduction, at least at this stage of development.^[77]

Comparison of the distribution of all tiger subspecies (1900 vs. 1990)

A second possible introduction site in Kazakhstan is the Ili River delta at the southern edge of Lake Balkhash. The delta is situated between the Saryesik-Atyrau Desert and the Taukum Desert and forms a large wetland of about 8,000 km² (3,100 sq mi). Until 1948, the delta was a refuge of the extinct Caspian tiger. Reintroduction of the Siberian tiger to the delta has been proposed. Large populations of wild boar inhabit the swamps of the delta. The reintroduction of the Bukhara deer, which was once an important prey, is under consideration. The Ili delta is therefore considered as a suitable site for introduction.^[78]

In 2010, Russia exchanged two captive Siberian tigers for Persian leopards with the Iranian government, as conservation groups of both countries agreed on reintroducing these animals into the wild within the next five years. This issue is controversial since only 30% of such releases have been successful. In addition, the Siberian tiger is not genetically identical to the Caspian tiger.^[9] Another difference is the climatic, with temperatures higher in Iran than in Siberia. Introducing exotic species into a new habitat could inflict irreversible and unknown damage.^[79] In December 2010, one of the tigers exchanged died in Eram Zoo in Tehran.^[80] Nevertheless, the project has its defenders, and Iran has successfully reintroduced the Persian onager and Caspian red deer.^[79]

In 2005, re-introduction was planned as part of the rewilding project at Pleistocene Park in the Kolyma River basin in northern Yakutia, Russia, provided the herbivore population has reached a size warranting the introduction of large predators.^[81]^[82]

In captivity

A tigress with cub in captivity in DierenPark Amersfoort

In recent years, captive breeding of tigers in China has accelerated to the point where the captive population of several tiger subspecies exceeds 4,000 animals. Three thousand specimens are reportedly held by 10–20 “significant” facilities, with the remainder scattered among some 200 facilities. This makes China home to the second largest captive tiger population in the world, after the U.S., which in 2005 had an estimated 4,692 captive tigers.^[83] In a census conducted by the U.S.-based Feline Conservation Federation, 2,884 tigers were documented as residing in 468 American facilities.^[84]

In 1986, the Chinese government established the world’s largest Siberian tiger breeding base, the Harbin Siberian Tiger Park, and was meant to build a Siberian tiger gene pool to ensure the genetic diversity of the tiger. The Park and its existing tiger population would be further divided into two parts, one as the protective species for genetic management and the other as the ornamental species. It was discovered that when the Heilongjiang Northeast Tiger Forest Park was founded it had only 8 tigers, but according to the current breeding rate of tigers at the park, the worldwide number of wild Siberian tigers will break through 1,000 in late 2010.^[85] South Korea expected to receive three tigers pledged for donation in 2009 by Russia in 2011.^[86]^[87]

Attacks on humans

Sign warns Caution! Tigers nearby! (Russian: Осторожно! Тигры рядoм!).

See also: Tiger attack

The Siberian tiger very rarely becomes a man-eater.^[11]^[63] Numerous cases of attacks on humans were recorded in the 19th century, occurring usually in central Asia excluding Turkmenistan, Kazakhstan and the Far East. Tigers were historically rarely considered dangerous unless provoked, though in the lower reaches of the Syr-Darya, a tiger reportedly killed a woman collecting firewood and an unarmed military officer whilst passing through reed thickets. Attacks on shepherds were recorded in the lower reaches of Ili. In the Far East, during the middle and late 19th century, attacks on people were recorded. In 1867 on the Tsymukha River, tigers killed 21 men and injured 6 others. In China’s Jilin Province, tigers reportedly attacked woodsmen and coachmen, and occasionally entered cabins and dragged out both adults and children.^[11]

A tiger family depicted in a Korean scroll from the late 18th century

According to the Japanese Police Bureau in Korea, in 1928 a tiger killed one human, whereas leopards killed three, wild boars four and wolves killed 48.^[88] Six cases were recorded in 20th century Russia of unprovoked attacks leading to man-eating behaviour. Provoked attacks are however more common, usually the result of botched attempts at capturing them.^[63] In December 1997, an injured Amur tiger attacked, killed and consumed two people. Both attacks occurred in the Bikin River valley. The anti-poaching task force Inspection Tiger investigated both deaths, tracked down and killed the tiger.^[89]

In January 2002, a man was attacked by a tiger on a remote mountain road near Hunchun in Jilin province, China, near the borders of Russia and North Korea. He suffered compound fractures but managed to survive. When he sought medical attention, his story raised suspicions as Siberian tigers seldom attack humans. An investigation of the attack scene revealed that raw venison carried by the man was left untouched by the tiger. Officials suspected the man to be a poacher who provoked the attack.^[90] The following morning, tiger sightings were reported by locals along the same road, and a local TV station did an on-site coverage. The group found tiger tracks and blood spoor in the snow at the attack scene and followed them for approximately 2,500 meters, hoping to catch a glimpse of the animal. Soon, the tiger was seen ambling slowly ahead of them. As the team tried to get closer for a better camera view, the tiger suddenly turned and charged, causing the four to flee in panic.^[91] About an hour after that encounter, the tiger attacked and killed a 26-year-old woman on the same road.^[92] Authorities retrieved the body with the help of a bulldozer. By then, the tiger was found lying 20 meters away, weak and barely alive.^[93] It was successfully tranquilized and taken for examination, which revealed that the tiger was anemic and gravely injured by a poacher’s snare around its neck, with the steel wire cutting deeply down to the vertebrae, severing both trachea and esophagus. Despite extensive surgery by a team of veterinarians, the tiger died of wound infection.^[94]^[95] Subsequent investigation revealed that the first victim was a poacher who set multiple snares that caught both the tiger and a deer.^[96] The man was later charged for poaching and harming endangered species. He served two years in prison.^[97] After being released from prison, he worked in clearing the forest of old snares.^[98]

In an incident at the San Francisco Zoo in December 2007, a tiger escaped and killed a visitor, and injured two others. The animal was shot by the police. The zoo was widely criticized for maintaining only a 12.5 ft (3.8 m) fence around the tiger enclosure, while the international standard is 16 ft (4.9 m). The zoo subsequently erected a taller barrier topped by an electric fence. One of the victims admitted to taunting the animal.^[99]

Zookeepers in Anhui province and the cities of Shanghai and Shenzhen were attacked and killed in 2010.^[100] In January 2011, a tiger attacked and killed a tour bus driver at a breeding park in Heilongjiang province. Park officials reported that the bus driver violated safety guidelines by leaving the vehicle to check on the condition of the bus.^[101] In September 2013, a tiger mauled a zookeeper to death at a zoo in western Germany after the worker forgot to lock a cage door during feeding time.^[102] In July 2020, a female tiger attacked and killed a 55-year-old zookeeper at the Zürich Zoo in Switzerland.^[103]

In culture

Heraldic arms of the Jewish Autonomous Oblast in Russia

The English name ‘Siberian tiger’ was coined by James Cowles Prichard in the 1830s.^[104] The name ‘Amur tiger’ was used in 1933 for Siberian tigers killed by the Amur River for an exhibition in the American Museum of Natural History.^[105]

The Tungusic peoples considered the tiger a near-deity and often referred to it as “Grandfather” or “Old man”. The Udege and Nanai people call it “Amba”.^[106] The Manchu considered the Siberian tiger as Hu Lin, the king.^[63] Since the tiger has a mark on its foreheads that looks like a Chinese character for ‘King’ (Chinese: 王; pinyin: Wáng), or a similar character meaning “Great Emperor”, it is revered by the Udege and Chinese people.^[11] The Siberian tiger is a national symbol of the Korean people due to its profound impact on traditional Korean culture.^[
March 20, 2025