Atlantic salmon
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| Salmo salar Linnaeus, 1758 |
Atlantic salmon, known scientifically as Salmo salar, is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the Atlantic.[1][2]
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[edit] Life stages
Most Atlantic salmon follow an anadromous fish migration pattern,[2] in that they undergo their greatest feeding and growth in salt water, but adults return to spawn in native freshwater streams where the eggs hatch and juveniles grow through several distinct stages.
Atlantic salmon do not require salt water, however, and numerous examples of fully freshwater ("landlocked") populations of the species exist throughout the Northern Hemisphere.[2] In North America, the landlocked strains are frequently known as ouananiche.
[edit] Freshwater phase
The freshwater phases of Atlantic salmon vary between 1 to 4 years, according to river location. While the young in southern rivers such as the English Channel are only one year old when they leave, those further north north such as in Scottish rivers can be over four years old. The average age correlates to temperature exceeding 7°C.[1]
The first phase is the alevin stage. During this phase, the fish stays in the breeding ground and uses the remaining nutrients in their yolk sack. During this developmental stage, the young grow and become active hunters. Once they are able to do so, they reach the fry stage. The fish grows and subsequently leaves the breeding ground in search of food. During this time, they move to areas with areas of higher prey concentration. The final freshwater stage is when they develop into parr in which they prepare for the trek to the Atlantic Ocean.
During these times, the Atlantic salmon are very susceptible to predation. Nearly 40% are eaten by trout alone. Other predators include other fish and birds.
[edit] Saltwater phases
When parr develop into smolt, they begin the trip to the ocean, which predominantly happens between March and June. Migration usually lasts at least 28 days. During this time, they become preyed upon largely by pike and gulls. The young salmon stage in estuaries and readily acclimate to the changing salinity. Once ready, young smolt leave, preferring an ebb tide.
Having left their natal streams, they experience a period of rapid growth during the 1 to 4 years they live in the ocean. Typically, Atlantic salmon migrates from its home stream to an area on the continental plate off West Greenland. During this time in the salmon's life, they face predation from Greenland sharks, skate, cod, and halibut. Some dolphins have been noticed playing with dead salmon, but it is still unclear whether they consume them.
Once large enough, Atlantic salmon change into the grilse phase where they become ready to return to precise fresh water tributary in which they were born. After returning to its natal stream the salmon will cease eating altogether prior to spawning. Although it is largely unknown how they return to the same spot, it has been suggested that odour — the exact chemical signature of that stream — plays an important rôle in this process. Once above around 250 g, the fish no longer become prey for birds and many fish, although seals do prey upon them. Seals that commonly eat Atlantic salmon are the Grey Seal and Common Seal. Survivabilty to this stage has been estimated at between 14 and 53%.[1]
[edit] Taxonomy
The Atlantic salmon was described to science by zoologist and taxonomist Carolus Linnaeus in 1758, one year after he was ennobled with the name Carl von Linné. It was not until later however that the differently coloured smolts were found to be the same species.
It was given its scientific binomial name by Linnaeus, Salmo salar, from the Latin words "Salmo" meaning salmon, and "salar" meaning "leaper".[3]
[edit] Physiology
The colouration of young Atlantic salmon does not resemble their adult stage. While they live in freshwater they have blue and red spots. While they mature they take on a silver blue sheen. When they are adults the easiest way of identifing them is by the black spots predominantly above the lateral line, although its caudal fin is usually unspotted. When they reproduce males take on a slight green or red coloration. The salmon has a fusiform body, and well developed teeth. All fins, save for the adipose, are bordered with black.
[edit] Distribution and habitat
In the United States and elsewhere, efforts to restore salmon to their native habitats are underway and there is some slow but steady progress. Restoration and protection of the habitat itself is key to this process. In the Great Lakes, Atlantic salmon have been introduced successfully, but the actual percentage of salmon reproducing naturally is very low. Most are stocked annually. Atlantic salmon were native to Lake Ontario but were extirpated by habitat loss and overfishing in the late 1800s. The state of New York has since been annually stocking its adjoining rivers and tributaries with the fish and in many cases do not allow active pursuit of the species.[2][4]
[edit] Diet
After hatching, young salmon begin a feeding response with a couple days. After the yolk sac is aborbed by the body, they begin to hunt. Juveniles start with tiny invertebrates, but as they mature they may occasionally eat small fishes. During this time they hunt both in the substrate, and also those in the current. Some have been known to also eat salmon eggs. The most commonly eaten foods include caddisflies, blackflies, mayflies, and stoneflies.[1]
In adulthood, fish feed on much larger food. Arctic squid, sand eels, amphipods, Arctic shrimp, and sometimes herring. During this feeding time the fish's size increases dramatically.[1]
[edit] Behaviour
Fry and parr have been said to be territorial, but evidence showing that they guard territories is inconclusive. While they may occasionally be aggressive towards each other, the social hierarchy is still unclear. Many have been found to school, especially when leaving the estuary.
Adult Atlantic salmon are considered much more aggressive than other salmon and are more likely to attack other fish than others. Where they have become an invasive threat it has become a concern that they are attacking native salmon such as Chinook salmon and Coho salmon.[1]
[edit] Breeding
Atlantic salmon breed in the rivers of Western Europe from Northern Portugal north to Norway, Iceland, Greenland, and the east coast of North America from Connecticut in the United States north to northern Labrador in Arctic Canada. At sea, it is found mainly in the waters off Greenland and in migrations to and from its natal streams.[1] Until the early 1800s, Atlantic salmon were native to the waters of central New York. When dams were constructed on the Oswego River their spawning areas were cut off and they went extinct in the area.
Unlike the various Pacific salmon species, the Atlantic salmon is iteropartic, which means the fish does not automatically die after spawning, and may recondition themselves, return to the sea to repeat the migration and spawning pattern several times.[5][2] Nevertheless, migration and spawning exact an enormous physiological toll on the individual fish, such that repeat spawners are the exception rather than the norm.[5]
[edit] Aquaculture
In its natal streams, Atlantic salmon are considered a prized recreational fish, pursued by avid fly anglers during its annual runs. At one time, the species supported an important commercial fishery and a supplemental food fishery. However, the wild Atlantic salmon fishery is commercially dead; after extensive habitat damage and overfishing, wild fish make up only 0.5% of the Atlantic salmon available in world fish markets. The rest are farmed, predominantly from aquaculture in Chile, Canada, Norway, Russia, the UK and Tasmania in Australia. Sport fishing communities mainly from Iceland and Scandinavia have joined in the North Atlantic Salmon Fund (NASF) to buy away commercial quotas in an effort to save the wild species of Salmo salar.[5]
[edit] Aquaculture techniques
Adult male and female fish are anaesthetized. Eggs and sperm are "stripped", after the fish are cleaned and cloth dried. Sperm and eggs are mixed, washed, and placed into fresh water. Adults recover in flowing, clean, well aerated water.[6] Some researchers have even studied cryopreservation of their eggs. [7]
Fry are generally reared in large freshwater tanks for 12 to 20 months. Once the fish have reached the smolt phase, they are taken out to sea where they are held for up to two years. During this time the fish grow and mature in large cages off the coasts of Canada, America, or parts of Europe.[5]
Generally, cages are made of two nets. Inner nets, which wrap around the cages, hold the salmon. Outer nets, which are held by floats, keep predators out.[6]
[edit] Controversy
Many Atlantic salmon inevitably escape from cages at sea. Those salmon who further breed tend to lessen the genetic diversity of the species leading to lower survival rates, and lower catch rates. On the West Coast, the non-native salmon can be an invasive threat, especially in Alaska and parts of Canada. This causes them to compete with native salmon for resources. Extensive efforts are underway to prevent escapes and the spread of Atlantic salmon in the Pacific and elsewhere.[4]
[edit] Human impact
Currently, overfishing, habitat loss and aquacultured salmon escapes are the greatest threats to natural Atlantic salmon populations.
In New England, many efforts are underway to restore salmon to the region by knocking down obsolete dams and updating others with fish ladders and other contraptions that have proven effective in the West with Pacific salmon. There is some success thus far, with populations growing in the Penobscot River and the Connecticut River. There has also been some success in establishing Atlantic salmon in Fish Creek, a tributary of Oneida Lake in central New York.
Atlantic salmon however, remains a popular fish for human consumtion.[2] It is commonly sold fresh, canned, or frozen.
[edit] Legislation
The first laws regarding the Atlantic salmon were started nearly 800 years ago.
[edit] England and Wales
Edward I instated a penalty for collecting salmon during certain times of the year. His son Edward II continued, regulating the constrution of weirs. Enforcement was overseen by those appointed by the Justices of the Peace. Because of confusing laws, and the fact that the appointed conservators had little power, most laws were barely enforced.
Based upon this, in 1860 a Royal Commission was appointed to thoroughly investigate the Atlantic Salmon and the laws governing the species. The results caused the 1861 Salmon Fisheries Act. The Salmon Fisheries Act placed control of inforcing the laws under the Home Office's control. Control however was later taken from the Home Office, and transferred to the Board of Trade and than later to the Board of Agriculture and Fisheries.
Another act was later passed in 1865 that imposed charges to fish and catch limits. It also caused the formation of local boards that had jusidiction over a certain river. The next significant act was passed in 1907 which allowed board to charge 'duties' to catch other freshwater fish, including trout.
Despite legislation, board decreased until in 1948 the River Boards Act gave authority of all freshwater fish and also the prevention of polution to one board per river. In total it created 32 boards altogether.
In 1974, all the 32 boards were reduced to 10 regional water authoritys (RWAs). Although only the Northumbrian, Welsh, north west and south west RWA's had considerable salmon population, all ten also cared for trout and freshwater eels.
The last significant law was passed. It was called the The Salmon and Freshwater Fisheries Act which passed in 1975. It, among other things, regulated fishing licences, fishing seasons, size limits, and banned obstructing the salmon's migratory paths.[1]
[edit] Scotland
Legislation in Scotland to help Atlantic salmon began in 1318 by Alexander II. It prohibited certain types of traps in rivers.
During the 15th century many laws were passed, many that regulated fishing times, and worked to ensure smolts could safely pass downstream. James III even closed a meal mill because of its history of killing fish attracted to the wheel. Because the fish was held in such high regard, poachers were severely punished. A poacher's punishment was lugging at the tron, which involved nailing a wooden shaft to one's ear for a time.
More recent legislation has established commissioners who manage disticts. Furthermoore, the Salmon and Freshwater Fisheries Act in 1951 required that the Secretary of State be given data about the catches of salmon and trout to help establish catch limits.[1][6]
[edit] United States of America
Fishing in the United States of America is controlled by the United States Fish and Wildlife Service, which was created in 1939.
The only act targeting the fish is the Atlantic Salmon Convention Act of 1982 which makes sure the Secretary of State receives reports, recommendations about laws regarding the species, and proposals from the group.
[edit] NASCO
North Atlantic Salmon Conservation Organization (NASCO) is an international council made up of Canada, Denmark, the European Union, Iceland, Norway, the Russian Federation, and the United States of America, with its headquarters in Edinburgh.[1] It was established in 1983 to help protect Atlantic salmon stocks, through the cooperation between nations. They work to restore habitat and promote conservation of the salmon.
[edit] References
- ^ a b c d e f g h i Shearer, W (1992). The Atlantic Salmon. Halstead Press.
- ^ a b c d e f (1983) The Audubon Society Field Guide to North American Fishes, Whales & Dolphins, 395.
- ^ Barton, M: "Biology of Fishes.", pages 198-202 Thompson Brooks/Cole 2007
- ^ a b Mills, D (1989). Ecology and Management of Atlantic Salmon. Springer-Verlag.
- ^ a b c d Heen, K (1993). Salmon Aquaculture. Halstead Press.
- ^ a b c Sedgwick, S (1988). Salmon Farming Handbook. Fishing News Books LTD.
- ^ Bromage, N: "Broodstock Management and Egg and Larval Quality" Blackwell Science 1995
[edit] Sources
- World Conservation Monitoring Centre (1996). Salmo salar. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006.
- Salmo salar (TSN 161996). Integrated Taxonomic Information System. Accessed on 30 January 2006.
- "Salmo salar". FishBase. Ed. Ranier Froese and Daniel Pauly. 10 2005 version. N.p.: FishBase, 2005.
[edit] External links
- Atlantic Salmon in Maine, report by the United States National Research Council (2004)
- The Atlantic Salmon Federation
- State of Maine, Atlantic Salmon Commission
- University of Massachusetts information regarding Atlantic salmon
- Atlantic salmon's page on World Wide Fund for Nature's webiste
- Alaska Fish and Game Atlantic salmon page
- Atlantic Salmon Trust, an organization working to protect the Atlantic salmon
