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. The
Kamchatka Peninsula, in the
Russian Far East, contains the world's greatest salmon sanctuary.
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
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. 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. Even in those species of salmon that may survive to spawn more than once , however, post-spawning mortality is quite high Those species average about two or, perhaps, three spawning events per individual.
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 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. 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 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.
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 female salmon excavates a shallow depression, called a
redd, in the gravel of the streambed wherein she lays her
eggs. The eggs usually range from orange to red in color. One or more males will approach the female as she deposits the eggs, fertilizing them. The female then covers the eggs by disturbing the gravel at the upstream edge of the depression. 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. 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.
At sea, before their first return to freshwater, the juveniles are called
grilse. They spend two to eight years in the open ocean where they will become sexually mature. The adult salmon returns to its natal stream to spawn. When fish return for the first time they are called
whitling in the
UK. Prior to spawning, depending on the species, the salmon undergoes changes. They may grow a hump, develop canine teeth, develop a
kype . 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.
The age of a salmon can be deduced from the growth rings on its scales, examined under the microscope. 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 analogous to the growth rings visible in a tree trunk. Freshwater growth shows as densely crowded rings; sea growth as widely spaced rings, 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 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.
Salmon as food
Salmon is a popular
food, and is reasonably healthy due to its high
protein and
Omega-3 fatty acids content and to its overall low
fat levels. According to reports in the journal
Science, however, farmed salmon may contain high levels of
dioxins. PCB levels may be up to 8 times higher in farmed salmon compared to wild salmon, and
Omega-3 content may also be lower than in wild caught individuals. Wild salmon are a healthy food, and according to the British FSA the benefits of eating even farmed salmon still outweigh the risks. It is also important to note that 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 are farmed , whereas the majority of
Pacific salmon are wild-caught .
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
astaxanthin in the flesh. Wild salmon get these carotenoids from eating
krill and other tiny
shellfish. The pigment is however, along with
canthaxanthin and other
Vitamins, added artificially as colourants to the feed of farmed salmon, because their given feed does not contain these pigments. Astaxanthin is a potent antioxidant that stimulates the health and development of fish nervous systems and improves the fish's fertility and growth. Canthaxanthin is known to have negative effects on the human eye, causing retina deposition in large intakes .
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 .
Raw salmon flesh may contain
Anisakis is a genus [i] of parasitic [i] nematode [i]s, which have a life cycle involving fish [i] a ...
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 and
sushi.
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:
- Disease transfer from open net cage salmon farming; especially sea lice. The European Commission 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 .
- 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 infections of the 1970s and 1980s which severely affected adult salmon in freshwater rivers.
- Loss of suitable freshwater habitat, especially suitable material for the excavation of redds.
- The construction of dams, weirs, barriers and other "flood prevention" measures frequently have severe adverse impacts on river habitat and on the accessibility of those habitats to salmon.
- 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 because of diversions and extractions, hydroelectric power generation, irrigation schemes etc.
There are efforts to relieve this situation. As such, several government and NGOs are sharing and participating in documentation efforts.
- NOAA's Office of Protected Resources maintains a , the Endangered Species Act
- Sweden has generated a protection program as part of its Biodiversity Action Plan
- maintains an IUCN redlist of
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
Norway,
Sweden,
Scotland,
Canada, and
Chile and is the source for most salmon consumed in America and Europe. Atlantic salmon are also farmed in
Russia and in
Tasmania,
Australia.
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 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.
Species
The various species of salmon have many names.
Atlantic Ocean species
Atlantic ocean species belong to the genus
Salmo. They include,
- Atlantic salmon or Salmon , is the species after which all the others are named.
- Land-locked salmon live in a number of lakes in eastern North America. This subspecies is non-migratory, even when access to the sea is not barred.
- 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
Pacific species belong to the genus
Oncorhynchus is a genus [i] of the family [i],
Salmonidae. ...
, some examples include;
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The
Klamath River, approximately 250 mi long, is a major river of the Pacific [i] coast in south ...
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 is also known locally as King, Tyee, Spring Salmon, Quinnat, Tule, or Blackmouth salmon.
- Pink salmon or Humpback salmon is found from northern California and Korea
One of the world's oldest civilization [i]s, Korea began with the founding of Gojoseon [i] in 2333 ...
, throughout the northern Pacific, and from the
Mackenzie River in Canada to the
Lena River in Siberia.
...
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 is found throughout the coastal waters of Alaska and British Columbia and up most clear-running streams and rivers.
- Cherry salmon is found only in the western Pacific Ocean in Japan, Korea and Russia.
Other species
- Huchen or Danube salmon , the largest permanent fresh water salmonid
External links
- University of Washington Libraries collection of documents describing salmon of the Pacific Northwest
- [pdf] , Kevin Ho, Columbia University, 2005.
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- A registered non-profit for sustainable development of salmon habitat in the Pacific Northwest.
- A salmon restoration organization.
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- [pdf] from the Monterey Bay Aquarium
- by Linda Joyce Forristal, worldandi.com, 2003 - Salmon specific.
- by Judith E. Foulke, FDA Consumer, September 1993 - General talk on consumer fraud in the fish industry, with a section on salmon coloring.
- A collection of food recipes containing salmon.
- Salmon recipes listed by cooking method.
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Further reading
- , Xanthippe Augerot and the State of the Salmon Consortium, University of California Press, 2005, hardcover, 152 pages, ISBN 0-520-24504-0
- Trout and Salmon of North America, Robert J. Behnke, Illustrated by Joseph R. Tomelleri, The Free Press, 2002, hardcover, 359 pages, ISBN 0-7432-2220-2
- , By Molly Cone, Sierra Club Books, 48 pages, ISBN 0-87156-572-2 - A book for juveniles describes the restoration of 'Pigeon Creek'.
- Salmon, Their Fight for Survival, By Anthony NetBoy, © 1973, Houghton Mifflin Co., 613 pages, ISBN 0-395-14013-7
