Salmon
Salmon is the common name for several species of fish of the Salmonidae family. Several other fishes 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. The Kamchatka Peninsula, in the Russian Far East, contains the world's greatest salmon sanctuary.
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 spawning in a stream were born there. In Alaska, the crossing over to other streams allows salmon to populate new streams, such as those that emerge as a glacier retreats. How they navigate is still a mystery, though their keen sense of smell may be involved. In all species of Pacific salmon, the mature individuals die within a few weeks of spawning.
Coastal dwellers have long respected the salmon. Most peoples of the Northern Pacific shores had a ceremony to honor the first return of the year. For many centuries, people caught the salmon as they swam upriver. 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. Long drift net fisheries have been banned on the high seas except off the coast of Ireland.
Salmon population levels are of concern in the Atlantic and 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.
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.
Life history
The wild salmon find mates in their native streams then the female salmon lays salmon eggs in the bottom gravel nests called redds. These eggs usually range from an orange to red in colour. The eggs are fertilized by the male and later 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 native stream before becoming smolts which are distinguished by their bright silvery colour with scales that are easlily rubbed off. 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 changes, allowing them to osmoregulate in the ocean.
At sea before their first return to freshwater they are called grilse. They migrate out into the ocean where they will develop in about two to eight years, (depending on the species) into mature salmon. After living and growing in the open ocean, the adult salmon will return to its native stream, breed, spawn and die. When fish return for the first time they are called whitling in the UK. When it matures prior to spawning, depending on the species, the salmon undergoes changes. They may grow a hump, develop canine teeth, develop a fytke ( large upgrowth of the lower jaw in male Atlantic Salmon). All will change from the silvery blue of a fresh run fish from the sea to a beautiful red colour. Condition tends to deteriorate the longer the fish are in freshwater and they then deteriorate further after they spawn becoming known as kelts. No one knows why they go back to the stream they were born in to die, but they make amazing journeys sometimes hundreds of miles inland and fight up against strong rapids to reproduce and start the next generation.
The ages of any salmon can be deduced from the growth rings on their scales when examined under the microscope. Freshwater growth shows as densely crowded rings; sea growth as widely spaced rings representing rapid growth and 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 survive. 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.
Environmental pressures
Many wild Salmon stocks have seen a marked decline in recent decades, especially the north Atlantic populations which spawn in western European waters. The cause of this decline is not well understood but is likely to include a number of factors including:
- The Faeroes and Greenland salmon netting industry
- Ocean and river warming which can delay spawning and accelerate transition to smolting.
- UDN infections of the 1970s and 1980s which severely impacted adult salmon in freshwater rivers.
- Loss of suitable freshwater habitat, especially suitable spawning redd material. Flood prevention measures frequently have severe adverse impacts on river habitat status.
- Loss of invertebrate diversity and population density in rivers because of modern farming methods and diverse pollution thus reducing food availability.
- Reduction in freshwater flow in rivers because of over abstraction, hydroelectricity generation, irrigation schemes etc.
- Man made obstructions in rivers such as dams and weirs.
Salmon as food
Salmon is a popular food, and reasonably healthy due to its high protein and Omega-3 fatty acids and its overall low fat levels. According to reports by Science, however, farmed salmon may contain high levels of dioxins. PCB ( Polychlorinated biphenyl) levels may also be up to 8 times higher in farmed salmon compared to wild salmon, and Omega-3 content may also be lower than wild caught species. Wild salmon are a healthy food, but according to the British FSA ( Food Standards Agency) the benefits of eating even farmed salmon still outweigh the risks. Also it is important to note, salmon is generally one of the least tainted by methylmercury of all fish.
A simple rule of thumb is that the vast majority of Atlantic salmon available on the world market is farmed (greater than 99%), whereas the majority of Pacific salmon is wild-caught (greater than 80%).
Salmon is generally a red-flesh fish, although there are some examples of white fleshed wild salmon. The natural colour of salmon results from carotenoids — astaxanthin and to a lesser degree, canthaxanthin — in the fish flesh. Wild salmon get these carotenoids from eating krill and other tiny shellfish. Farm salmon get them in their feed, along with other essential nutrients. Astaxanthin is a potent antioxidant that also stimulates fish nervous systems and improves fertility and growth.
Canned salmon in the U.S. is usually wild Pacific catch, though some farmed salmon is available in canned form. Alaskan salmon is always wild catch. 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 meat may contain anisakidae, marine parasites that cause Anisakiasis. Before the availability of refrigeration, Japanese did not consume raw salmon. Salmon and salmon roes were not used to make sashimi (raw fish) and sushi until recently.
 Poached salmon |
 White Alaskan Salmon |
 Salmon roe at the Shiogama seafood market in Japan |
 Ovary of the salmon was opened and loosened |
Aquaculture
Salmon is a minor contributor in the world production of finfish aquaculture which includes many other species like: tilapia, sea bass, carp, bream, and trout. Salmon are carnivorous and are currently fed a meal produced from catching other wild fish, so as the number of farmed salmon increase, the demand for other fish to feed the salmon increases. 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 spread to local wild salmon stocks. Alaska has developed a safer form of salmon production called ocean ranching. Salmon are raised in hatcheries until they are old enough to become independent. They are released into the ocean far from any wild salmon streams, then they are free to live and develop fully out in the open ocean until it is time for them to complete the normal salmon cycle of returning to fresh water to spawn and die. When they sense they are going to spawn they immediately return to where they were released. Local fishermen catch them when they return.
Species
The various species of salmon have many names.
Atlantic Ocean species
- Atlantic salmon or Salmon (Salmo salar), is the species after which all the others are named.
- Land-locked salmon (Salmo salar sebago) live in a number of lakes in eastern North America. This subspecies is non-migratory, even when access to the sea is not barred.
- Another Atlantic species, Salmo trutta, is usually classified as a trout, despite being a closer relative of Atlantic Salmon than any of the Pacific species of salmon. See Brown trout.
Pacific Ocean species
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? Pacific Ocean
Salmon |
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 Sockeye
Salmon
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Species
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nerka O. tshawytscha O. gorbuscha O. keta O. kisutch O. masou |
- Sockeye salmon (Oncorhynchus nerka) is known locally as "Red Salmon" or "Blueback Salmon." This species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaido 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.
- Chinook salmon (Oncorhynchus tshawytscha) is also known locally as King, Tyee, Spring Salmon, Quinnat, Tule, or Blackmouth salmon.
- Pink salmon or Humpback salmon (Oncorhynchus gorbuscha) is found from northern California and Korea, throughout the northern Pacific, and from the Mackenzie River in Canada to the Lena River in Siberia.
- Chum salmon (Oncorhynchus keta) is known locally as Dog or Calico salmon. This species has a wide geographic range: south to the Sacramento River in California in the eastern Pacific and the island of Kyushu 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 or Silver salmon (Oncorhynchus kisutch) is found throughout the coastal waters of Alaska and British Columbia and up most clear-running streams and rivers.
- Cherry salmon (Oncorhynchus masu or O. masou) is found only in the western Pacific Ocean in Japan, Korea and Russia.