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Atlantic salmon

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Atlantic salmon
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Salmoniformes
Family:
Salmonidae
Genus:
Salmo
Species:
S. salar
Binomial name
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 and the Pacific.[1][2]

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.

Freshwater phase

A newly hatched Atlantic salmon alevin which, in around 24 hours, will absorb the yolk sack and become a fry

The freshwater phases of Atlantic salmon vary between 1 to 5 years, according to river location. While the young in southern rivers, such as those to the English Channel, are only one year old when they leave, those further 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 gills 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.

Saltwater phases

When parr develop into smolt, they begin the trip to the ocean, which predominantly happens between March and June. Migration usually acclimatise 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 humans, 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. Survivability to this stage has been estimated at between 14 and 53%.[1]

Nomenclature

The Atlantic salmon was given its scientific binomial name by zoologist and taxonomist Carolus Linnaeus in 1758. It was not until later, however, that the differently coloured smolts were found to be the same species.

The name, Salmo salar, is from the Latin "Salmo", meaning salmon, and "salar", meaning "leaper".[3]

Physiology

An adult Atlantic salmon displaying its black spotting and blue colouration

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 identifying 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 colouration. The salmon has a fusiform body, and well developed teeth. All fins, save for the adipose, are bordered with black.

Distribution and habitat

Around the North Atlantic, 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 but issues of excessive harvest and competition with farmed and escaped salmon are also primary considerations. 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 19th century. 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]. Wild salmon on entering rivers as adults [1]have characteristically pointed fins which help scientists distinguish from farmed or escaped salmon.

Diet

After hatching, young salmon begin a feeding response within a couple days. After the yolk sac is absorbed 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]

Behavior

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]

Breeding

Very young fertilised salmon eggs; notice the developing eyes and vertebral column.

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 and Arctic Canada. Atlantic salmon which have escaped from the aquaculture industry have also been found breeding in rivers tributary to the Pacific Ocean in British Columbia on Canada's west coast. At sea, the species 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 iteroparous, 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]

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]

Aquaculture techniques

File:Salmon farming.jpg
An Atlantic salmon farm which holds yearlings for up to two years. Many hold broodstock for even longer in these conditions to help ensure large, sexually mature adults.

Adult male and female fish are anaesthetised. 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, the USA, 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]

Controversy

Many Atlantic salmon 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 of Northern America, 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]

Human impact

Salmon decline in Lake Ontario goes back to the 1700s-1800s, due to logging, soil erosion, as well as dam and mill construction. By 1896 the species was declared extirpated from the lake.[8]

In the 1950s it was discovered that salmon from rivers in the US and Canada, as well as from Europe, gathered in the sea around Greenland and the Faroe Islands. A massive commercial fishing industry was established, taking salmon in drift nets. After an initial series of record annual catches, the numbers crashed: between 1979 and 1990, catches fell from four million to 700,000.[9]

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. In Ontario, the Atlantic Salmon Restoration Program was started in 2006 and is one of the largest freshwater conservation programs in North America. It has stocked Lake Ontario with over 700,000 young Atlantic salmon. In November 2007, a migrating salmon was observed in the Credit River.[10] 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 consumption.[2] It is commonly sold fresh, canned, or frozen.

Legislation

The first laws regarding the Atlantic salmon were started nearly 800 years ago.

England and Wales

Edward I instated a penalty for collecting salmon during certain times of the year. His son Edward II continued, regulating the construction 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 enforcing 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 then 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 jurisdiction 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 pollution to one board per river. In total it created 32 boards altogether.

In 1974, all the 32 boards were reduced to 10 regional water authorities (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 Salmon and Freshwater Fisheries Act was passed in 1975. Among other things, it regulated fishing licences, fishing seasons, size limits, and banned obstructing the salmon's migratory paths.[1]

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.

More recent legislation has established commissioners who manage districts. Furthermore, 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]

United States

Fishing in the United States is controlled by the United States Fish and Wildlife Service, and by NOAA Fisheries.

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.

Several populations of Atlantic Salmon are in serious decline, and are listed as threatened under the Endangered Species Act.

Quebec

In Quebec, the daily catch limit for Atlantic salmon is 1 fish over 63 cm, 2 fish under 63 cm or 1 fish over and 1 under 63 cm, provided that the smaller fish was the first one caught (a provision designed to prevent an angler from continuing to fish if a large fish is already in possession). The annual catch limit is 7 Atlantic salmon of any size.

NASCO

The 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, with its headquarters in Edinburgh [2]. 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.

References

  1. ^ a b c d e f g h i Shearer, W (1992). The Atlantic Salmon. Halstead Press.
  2. ^ a b c d e f The Audubon Society Field Guide to North American Fishes, Whales & Dolphins. Chanticleer Press. 1983. p. 395.
  3. ^ Barton, M: "Biology of Fishes.", pages 198-202 Thompson Brooks/Cole 2007
  4. ^ a b Mills, D (1989). Ecology and Management of Atlantic Salmon. Springer-Verlag.
  5. ^ a b c d Heen, K (1993). Salmon Aquaculture. Halstead Press.
  6. ^ a b c Sedgwick, S (1988). Salmon Farming Handbook. Fishing News Books LTD.
  7. ^ N. Bromage (1995). Broodstock Management and Egg and Larval Quality. Blackwell Science.
  8. ^ Harb, M. "Upstream Battle", Canadian Geographic Magazine, June 2008, p. 24
  9. ^ "Salmon campaigner lands top award". BBC News. 2007-04-22. {{cite news}}: Check date values in: |date= (help); Cite has empty unknown parameter: |1= (help)
  10. ^ Harb, M. "ibid", p. 24

Sources

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