Salmon

From Wikipedia, the free encyclopedia

Salmon is the common name for several species of fish of the family Salmonidae. Several other fish in the family are called trout. Salmon live in both the Atlantic and Pacific Oceans, as well as the Great Lakes and other land locked lakes.

Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. Folklore has it that the fish return to the exact spot where they were born to spawn, and modern research shows that usually at least 90% of the fish that spawn in a particular stream were born there.^{[citation needed]} In Alaska, the crossing over to other streams allows salmon to populate new streams, such as those that emerge as a glacier retreats. The precise method salmon use to navigate has not been entirely established, though their keen sense of smell is certainly involved. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. However, even in those species of salmon that may survive to spawn more than once (iteroparity), post-spawning mortality is quite high (perhaps as high as 40 to 50%.) Those species average about two or, perhaps, three spawning events per individual.^{[citation needed]}

Salmon has long been at the heart of the culture and livelihood of coastal dwellers. Most peoples of the Northern Pacific shore had a ceremony to honor the first return of the year. For many centuries, people caught salmon as they swam upriver to spawn. A famous spearfishing site on the Columbia River at Celilo Falls was inundated after great dams were built on the river. The Ainu, of northern Japan, taught dogs how to catch salmon as they returned to their breeding grounds en masse. Now, salmon are caught in bays and near shore. Drift net fisheries have been banned on the high seas except off Northumberland on the east coast of England.^{[citation needed]}

Salmon population levels are of concern in the Atlantic and in some parts of the Pacific but in northern British Columbia and Alaska stocks are still abundant. The Skeena River alone has millions of wild salmon returning which support commercial fisheries, aboriginal food fisheries, sports fisheries and the area's diverse wildlife on the coast and around communities hundreds of miles inland in the watershed. The Columbia River salmon population is now less than 3% of what it was when Lewis and Clark arrived at the river.^[1]

Both Atlantic and Pacific Salmon are important to recreational fishing around the world.

In the southern hemisphere, there is the Australian salmon, which is a salt water species not related in any way to the salmonidae. It is found along the southern coastline of Australia and Tasmania. Commonly caught there with large beach nets, its use as a commercial fish has been declining over the last 20 years.

[edit] Life history of salmon

In order to lay her roe, the female salmon uses her tail fin to excavate a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering 30 square feet.^[2] The eggs usually range from orange to red in color. One or more males will approach the female in her redd, depositing his sperm, or milt, over the roe.^[3] 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 will make as many as 7 redds before her supply of eggs is exhausted. The salmon then die within a few days of spawning.^[3]

The eggs will hatch into alevin or sac fry. The fry quickly develop into parr with camouflaging vertical stripes. The parr stay for one 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. It is estimated that only 10% of all salmon eggs survive long enough to reach this stage.^[4] The smolt body chemistry changes, allowing them to live in salt water. Smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to osmoregulation in the ocean.

The salmon spend one to five years (depending on the species) in the open ocean where they will become sexually mature. The adult salmon returns primarily to its natal stream to spawn. When fish return for the first time they are called whitling in the UK and grilse or peel in Ireland. Prior to spawning, depending on the species, the salmon undergoes changes. They may grow a hump, develop canine teeth, develop a kype (a pronounced curvature of the jaws in male salmon). All will change from the silvery blue of a fresh run fish from the sea to a darker color. Condition tends to deteriorate the longer the fish remain in freshwater, and they then deteriorate further after they spawn becoming known as kelts. 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 900 miles and climb nearly 7000 feet from the Pacific ocean as they return to spawn.

The age of a salmon can be deduced from the growth rings on its scales, examined under the microscope.^{[citation needed]} Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in rings (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 conditions, 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.

How does a salmon get its red colour? The red colour of salmon is due to a pigment called astaxanthin .

A salmon is basically a white fish. The red pigment is made by algae and single cell organisms, which are eaten by shrimps; the pigment is then stored in their shell and flesh. When salmon eat shrimps they also accumulate the pigment in their fatty tissue. In view of the fact that salmon do not lose the pigment, they will turn red in time. As the diet of salmon differs, a tremendous variety of colours exist in natural salmon, ranging from light pink to deep red.

Most salmon these days are cultured. This takes place in large nets in quiet waters (fjords, bays) or in tanks on land. Most cultured salmon come from Norway, Scotland, Iceland, Alaska and Chile. These salmon are mainly fed with fishmeal. This does not contain shrimp, which means the salmon will stay white. The consumer, however, does not want white salmon, even though the taste is the same. For this reason astaxanthin is added to salmon feed. In most cases the astaxanthin is made chemically; alternatively it is extracted from shrimp flour. Another possibility is the use of dried red yeast, which provides the same pigment. However, the synthetic mixture is cheaper

Astaxanthin is a carotenoid, meaning it is a compound similar to carotene. Other carotenoids are responsible for the colour of tomatoes, peppers and carrots. Humans also store astaxanthin in fatty tissues, but we do not get enough into our system to turn red. Flamingos owe their red colour to astaxanthin in the same way as salmon do.

[edit] Salmon as food

Salmon is a popular food. Consuming salmon is considered to be reasonably healthy due to the fish's high protein and low fat levels and to its high Omega-3 fatty acids content. Salmon is also a source of cholesterol, ranging 23 - 214 mg/100g depending on the species [1]. According to reports in the journal Science, however, farmed salmon may contain high levels of dioxins. PCB (polychlorinated biphenyl) levels may be up to eight times higher in farmed salmon than in wild salmon, and Omega-3 content may also be lower than in wild caught individuals. According to a 2006 study published in the Journal of the American Medical Association, however, the benefits of eating even farmed salmon still outweigh any risks imposed by contaminants [2]. It is also noteworthy that wild salmon generally has among the lowest methylmercury contamination levels of all fish.^{[citation needed]} A simple rule of thumb is that the vast majority of Atlantic salmon available on the world market are farmed (greater than 99%), whereas the majority of Pacific salmon are wild-caught (greater than 80%). Farmed salmon outnumber wild salmon 85 to 1.^[5]

[edit] Environmental pressures

Many wild Salmon stocks have seen a marked decline in recent decades, especially north Atlantic populations which spawn in western European waters, and wild salmon of the Snake River system in the Northwest USA. The causes of these declines likely include a number of factors, among them:

• Disease transfer from open net cage salmon farming, especially sea lice. The European Commission (2002) concluded “The reduction of wild salmonid abundance is also linked to other factors but there is more and more scientific evidence establishing a direct link between the number of lice-infested wild fish and the presence of cages in the same estuary.” See Scientific Evidence.
• Overfishing in general but especially commercial netting in the Faroes and Greenland.
• Ocean and river warming which can delay spawning and accelerate transition to smolting.
• Ulcerative dermal necrosis (UDN) infections of the 1970s and 1980s which severely affected adult salmon in freshwater rivers.
• Loss of suitable freshwater habitat, especially degradation of stream pools and reduction of suitable material for the excavation of redds.
• The construction of dams, weirs, barriers and other "flood prevention" measures, which bring severe adverse impacts to river habitat and on the accessibility of those habitats to salmon. This is particularly true in the northwest USA, where large numbers of dams have been built in many river systems, including over 400 in the Columbia River Basin.
• Loss of invertebrate diversity and population density in rivers because of modern farming methods and various sources of pollution, thus reducing food availability.
• Reduction in freshwater base flow in rivers and disruption of seasonal flows, because of diversions and extractions, hydroelectric power generation, irrigation schemes, and slackwater reservoirs, which inhibit normal migratory processes and increase predation for salmon.

There are efforts to relieve this situation. As such, several government and NGOs are sharing in research and habitat restoration efforts.

• NOAA's Office of Protected Resources maintains a list of Endangered Species, the Endangered Species Act
• Sweden has generated a protection program as part of its Biodiversity Action Plan
• State of Salmon maintains an IUCN redlist of endangered salmon

• The Kamchatka Peninsula, in the Russian Far East, contains the world's greatest salmon sanctuary.

• Bear Lake, Alaska, is the site of salmon enhancement activities since 1962.^[6]

Salmon flesh is generally orange to red in colour, although there are some examples of white fleshed wild salmon. The natural colour of salmon results from carotenoid pigments, largely astaxanthin (E161j), in the flesh.^[7] Wild salmon get these carotenoids from eating krill and other tiny shellfish. Because consumers have shown a reluctance to purchase white fleshed salmon, astaxanthin, and very minutely canthaxanthin (E161g)), are added as artificial colourants to the feed of farmed salmon because prepared diets do not naturally contain these pigments. Astaxanthin is a potent antioxidant that stimulates the development of healthy fish nervous systems and that enhances the fish's fertility and growth rate. Research has revealed canthaxanthin may have negative effects on the human eye, accumulating in the retina at high levels of consumption.^[7] Today the concentration of carotenoids (mainly canthaxanthin and astaxanthin) exceeds 8 mg/kg of flesh and all fish producers try to reach a level that represents a value of 16 on the "Roche Color Card", a colour card used to show how pink the fish will appear at specific doses. This scale is specific for measuring the pink colour due to astaxanthin and is not for the orange hue obtained with canthaxanthin. The development of processing and storage operations, which can be detrimental on canthaxanthin flesh concentration, has led to an increased quantity of pigments added to the diet to compensate for the degrading effects of the processing. In wild fish, carotenoid levels of up to 20-25 mg are present, but levels of canthaxanthin are, in contrast, minor.^[7]

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 either to cold smoked salmon or to salmon cured in a brine solution (also called gravlax).

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.

[edit] Aquaculture

Salmon aquaculture is the major economic contributor to the world production of farmed fin-fish, representing over $1 billion US annually. Other commonly cultured fish species include: tilapia, catfish, sea bass, carp, bream, and trout. Salmon farming is very big in Chile, Norway, Sweden, Scotland,and Canada, and is the source for most salmon consumed in America and Europe. Atlantic salmon are also farmed in Russia, Tasmania, Australia and the UK.

Salmon are carnivorous and are currently fed a meal produced from catching other wild fish and other marine organisms. Consequently, as the number of farmed salmon increase, so does the demand for other fish to feed the salmon. Work continues on substituting vegetable proteins for animal proteins in the salmon diet. Unfortunately though, this substitution results in lower levels of the highly valued Omega-3 content in the farmed product. Intensive salmon farming now uses open net cages which have low production costs but have the drawback of allowing disease and sea lice to spread to local wild salmon stocks.

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 then released into rivers, often in an attempt to increase the salmon population. This practice was very common in countries like 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, limiting a company's chances of benefiting financially from their investment. Because of this, the method has mainly been used by various public authorities as a way of artificially increasing salmon populations in situations where they have declined due to overharvest, construction of dams, and habitat destruction or disruption. Unfortunately, there can be negative consequences to this sort of population manipulation, including genetic "dilution" of the wild stocks, and 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 then catch them.

[edit] Species

The various species of salmon have many names, and varying behaviors.

[edit] Atlantic Ocean species

Atlantic ocean species belong to the genus Salmo. They include,

• Atlantic salmon or Salmon (Salmo salar), is the species after which all the others are named.

[edit] Pacific Ocean species

Pacific species belong to the genus Oncorhynchus, some examples include;

• Cherry salmon (Oncorhynchus masu or O. masou) is found only in the western Pacific Ocean in Japan, Korea and Russia and also landlocked in central Taiwan's Chi Chia Wan Stream. ^[8]
• Chinook salmon (Oncorhynchus tshawytscha) is also known locally as King, Tyee, Spring salmon, Quinnat, Tule, or Blackmouth salmon. Chinook are the largest of all Pacific salmon, frequently exceeding 30 lbs. (14 kg).^[9]
• Chum salmon (Oncorhynchus keta) is known locally as Dog or Calico salmon. This species has the widest geographic range of the Pacific species^[10] : south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific; north to the Mackenzie River in Canada in the east and to the Lena River in Siberia in the west.
• Coho salmon (Oncorhynchus kisutch) is also known locally as Silver salmon. This species is found throughout the coastal waters of Alaska and British Columbia and up most clear-running streams and rivers.
• Pink salmon (Oncorhynchus gorbuscha), known as humpies in south east Alaska, are found from northern California and Korea, throughout the northern Pacific, and from the Mackenzie River in Canada to the Lena River in Siberia, usually in shorter coastal streams. It is the smallest of the Pacific species, with an average weight of 3.5 to 4 lbs. (1.6 - 1.8 kg).^[11]
• Sockeye salmon (Oncorhynchus nerka) is known in the USA as Red salmon.^[12] This lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō Island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish, shrimp and squid; sockeye feed on plankton that they filter through gill rakers.^[3]
• Steelhead or Steelhead trout or Rainbow trout (Oncorhychus mykiss) are river spawners, usually found in the same rivers that produce chinook, especially the Columbia, Snake, Skeena, and other large rivers on the Pacific Coast. Steelhead have also been introduced into some rivers surrounding the Laurentian Great Lakes.

[edit] Other species

• Land-locked salmon (Salmo salar sebago) live in a number of lakes in eastern North America. This subspecies of Atlantic Salmon is non-migratory, even when access to the sea is not barred.
• Kokanee salmon is a land-locked form of sockeye salmon.
• Huchen or Danube salmon (Hucho hucho), the largest permanent fresh water salmonid

[edit] Salmon in mythology

In Norse mythology, when Loki, god of mischief and strife, killed Baldr, god of beauty and light, he jumped into the river and transformed himself into a salmon in order 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.^[13]

In the mythology of the Gaels, the hero Fionn mac Cumhaill, leader of the Fianna, gained powers of perception from a salmon. The young Fionn met the poet Finegas, near the river Boyne and studied under him. Finegas had spent seven years trying to catch the salmon of knowledge, which lived in a pool on the Boyne: whoever ate the salmon would gain all the knowledge in the world. Eventually he caught it, and told the boy to cook it for him. While cooking it Fionn burst a blister on the salmons skin, burning his thumb, and instinctively put his thumb in his mouth, swallowing a piece of the salmon's skin. This imbued him with the salmon's wisdom.^[14]

[edit] Salmon in popular culture

• "The Salmon Dance", a 2007 single by The Chemical Brothers, features fun facts about salmon and a dance. The video shows a salmon lip-syncing to the lyrics, rapped by Fat Lip.