Atlantic salmon

Atlantic salmon
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Salmoniformes
Family: Salmonidae
Genus: Salmo
Species: S. salar
Binomial name
Salmo salar
Linnaeus, 1758

The Atlantic salmon (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 north Atlantic and (due to human introduction) the north Pacific.[1][2]

It is also commercially known as bay salmon, black salmon, caplin-scull salmon, fiddler, grilse, grilt, kelt, landlocked salmon, ouananiche, outside salmon, parr, Sebago salmon, silver salmon, slink, smolt, spring salmon or winnish.[3]

Contents

Life stages

Most Atlantic salmon follow an anadromous fish migration pattern,[2] in that they undergo their greatest feeding and growth in salt water; however, 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

The freshwater phases of Atlantic salmon vary between one and eight years, variably according to river location.[4] 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, and in Ungava Bay, northern Quebec, smolts as old as 8 years have been encountered.[4] The average age correlates to temperature exceeding 7 °C (45 °F).[1]

The first phase is the alevin stage, when the fish stay in the breeding ground and use the remaining nutrients in their yolk sac. During this developmental stage, the young gills develop and they become active hunters. Next is the fry stage, where the fish grow and subsequently leave the breeding ground in search of food. During this time, they move to areas with 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 allows acclimation 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 one to four years they live in the ocean. Typically, Atlantic salmon migrate from their home streams to an area on the continental plate off West Greenland. During this time, they face predation from humans, Seals, 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 their natal streams, the salmon will cease eating altogether prior to spawning. Although largely unknown, odor — the exact chemical signature of that stream — is suspected to play an important role in how salmon return to the area where they hatched. 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 gray and common seals. 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 Carl 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," according to M. Barton,[5] but more likely meaning "resident of salt water." Lewis and Short's Latin Dictionary (Clarendon Press, Oxford, 1879) translates `salar' as meaning `a kind of trout' from its use in the `Idylls' of the poet Ausonius (4th Century CE).

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 adult, the easiest way of identifying them is by the black spots predominantly above the lateral line, although the 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 the adipose, are bordered with black.

Distribution and habitat

Beginning around 1990 the rates of Atlantic salmon mortality at sea more than doubled, and by 2000 the numbers of Atlantic salmon had dropped to critically low levels.[7] In the western Atlantic fewer than 100,000 of the important multi-sea-winter salmon were returning. Rivers of the coast of Maine, plus southern New Brunswick and much of mainland Nova Scotia saw runs drop precipitously, and even disappear.

Beginning in the mid-1990s the Atlantic Salmon Federation in cooperation with partners were developing sonic tracking technology, and by 2008 the salmon have been tracked from rivers such as the Restigouche and the Miramichi as far along their migration routes as the Strait of Belle Isle, between Labrador and Newfoundland - and half way to feeding grounds in Greenland.

For whatever reasons, possibly related to improvements in ocean feeding grounds, returns in 2008 have been very positive. On the Penobscot returns had been about 940 in 2007, and by mid-July 2008 the return was 1,938. Similar stories were played out in rivers from Newfoundland to Quebec.

The problems at sea remain, and there is a concerted international effort called SALSEA, to find out more about the mortality at sea. It is organized by the North Atlantic Salmon Conservation Organization (NASCO).

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 does not allow active pursuit of the species.[2][8] Wild salmon on entering rivers as adults have characteristically pointed fins which help scientists distinguish from farmed or escaped salmon.

Diet

Young salmon begin a feeding response within a few 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 fish. During this time, they hunt both in the substrate and in the current. Some have been known to eat salmon eggs. The most commonly eaten foods include caddisflies, blackflies, mayflies, and stoneflies.[1]

As adults, the fish feed on much larger food: Arctic squid, sand eels, amphipods, Arctic shrimp, and sometimes herring, and the fishes' size increases dramatically.[1]

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]

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 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. The species constructs a nest or "redd" in the gravel bed of a stream. The female creates a powerful downdraught of water with her tail near the gravel to excavate a depression. After she and a male fish have respectively shed eggs and milt (sperm) upstream of the depression, the female again uses her tail, this time to shift gravel to cover the eggs and milt which have lodged in the depression. 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 19th century, 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 locally.

Unlike the various Pacific salmon species which die after spawning semelparous, 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, although most spawn once or twice.[2][9] Nevertheless, migration and spawning exact an enormous physiological toll on the individual fish, such that repeat spawners are by far the exception rather than the norm.[9] Atlantic salmon show high diversity in age of maturity and may mature as parr, 1–5 sea-winter fish, and in rare instances, at older sea ages. All these ages at maturity may occur in the same population, constituting a ‘bet hedging’ strategy against variation in stream flows.[4]

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 Norway, Chile, Canada, the UK, Faroe Islands, Russia 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.[9]

Aquaculture techniques

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.[10] Some researchers have even studied cryopreservation of their eggs.[11]

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.[9]

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.[10]

Controversy

In the past some Atlantic salmon have escaped from cages at sea. In the Atlantic Ocean this has resulted in some breeding with native populations but generally most surviving offspring were from the domesticated Atlantics, not hybrids.

On the West Coast of Northern America, Aquaculturists have taken great care to ensure the non-native salmon cannot escape from their open net pens and it is now not considered a major concern. There is no evidence that Atlantic salmon can survive and establish wild populations in the Pacific. "From 1905 until 1935 in excess of 8.6 million Atlantic salmon of various life stages (predominantly advanced fry) were intentionally introduced to more than 60 individual B.C. lakes and streams. Historical records indicate that in a few instances mature sea-run Atlantic salmon were captured in the Cowichan River, however a self-sustaining population never materialized. Environmental assessments by the U.S. National Marine Fisheries Service, the Washington Department of Fish and Wildlife and the B.C. Environmental Assessment Office have concluded that the potential risk of Atlantic salmon colonization in the Pacific Northwest is low.[12]

Human impact

Salmon decline in Lake Ontario goes back to the 18th-19th centuries, due to logging and soil erosion, as well as dam and mill construction. By 1896, the species was declared extirpated from the lake.[13]

In the 1950s, salmon from rivers in the US and Canada, as well as from Europe, were discovered to gather 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.[14]

Currently, overfishing, habitat loss and aquacultured salmon escapes are the greatest threats to natural Atlantic salmon populations. Overfishing at sea is generally considered the primary negative factor, however, even though marine exploitation rates estimated for various Newfoundland stocks for the period 1984–1991 averaged 45% on small (<63 cm) salmon and 74.2% on large salmon (>63 cm), closure of the Newfoundland commercial salmon fishery beginning in 1992 has not resulted in general increases in salmon populations through the present.[7]

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 and Connecticut Rivers. In Ontario, the Atlantic Salmon Restoration Program[15] 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 October 2007 salmon was video recorded running in Toronto's Humber River by the Old Mill. In November 2007, a migrating salmon was observed in the Credit River.[13] 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.

Beaver impact

The decline in anadromous salmonid species over the last two to three centuries is correlated with the decline in the North American beaver and European beaver, although some fish and game departments continue to advocate removal of beaver dams as potential barriers to spawning runs. Migration of adult Atlantic salmon may be limited by beaver dams during periods of low stream flows, but the presence of juvenile Salmo salar upstream from the dams suggests the dams are penetrated by parr.[16] Downstream migration of Atlantic salmon smolts was similarly unaffected by beaver dams, even in periods of low flows.[16] A 2003 study of Atlantic salmon and sea trout (Salmo trutta morpha trutta) spawning in the Numedalslågen River and 51 of its tributaries in southeastern Norway were unhindered by beaver.[17] In a restored, third-order stream in northern Nova Scotia, beaver dams generally posed no barrier to Atlantic salmon migration except in the smallest upstream reaches in years of low flow where pools were not deep enough to enable the fish to leap the dam or without a column of water over-topping the dam for the fish to swim up.[18] The importance of winter habitat to salmonids afforded by beaver ponds may be especially important (and underappreciated) in streams of northerly latitudes without deep pools where ice cover makes contact with the bottom of shallow streams.[16] In addition, the up to 8 year long residence time of juveniles in freshwater may make beaver-created permanent summer pools a crucial success factor for Atlantic salmon populations. In fact, two year-old Atlantic salmon parr in beaver ponds in eastern Canada showed faster summer growth in length and mass and were in better condition than parr upstream or downstream from the pond.[19]

Legislation

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

England and Wales

Edward I instituted 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 appointed conservators having little power, most laws were barely enforced.

Based upon this, a Royal Commission was appointed in 1860 to thoroughly investigate the Atlantic salmon and the laws governing the species, resulting in the 1861 Salmon Fisheries Act. The act placed enforcement of the laws under the Home Office's control, but it 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 passed in 1865 imposed charges to fish and catch limits. It also caused the formation of local boards having jurisdiction over a certain river. The next significant act, passed in 1907, allowed the board to charge 'duties' to catch other freshwater fish, including trout.

Despite legislation, board effects decreased until, in 1948, the River Boards Act gave authority of all freshwater fish and the prevention of pollution to one board per river. In total, it created 32 boards.

In 1974, all the 32 boards were reduced to 10 regional water authorities (RWAs). Although only the Northumbrian, Welsh, northwest and southwest RWA's had considerable salmon populations, 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, seasons, and 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 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 were 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 the Secretary of State be given data about the catches of salmon and trout to help establish catch limits.[1][10]

United States

Several populations of Atlantic salmon are in serious decline, and are listed as endangered under the Endangered Species Act (ESA). Currently, runs of 11 rivers in Maine are on the list - Kennebec, Androscoggin, Penoboscot, Sheepscot, Ducktrap, Cove Brook, Pleasant, Narraguagus, Machias, East Machias and Dennys. The Penobscot is the "anchor river" for Atlantic salmon populations in the US. Returns in 2008 have been around 2,000, more than double the 2007 return of 940.

Section 9 of the ESA makes it illegal to take an endangered species of fish or wildlife. The definition of "take" is to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct".[20]

Canada

The federal government has prime responsibility for protecting the Atlantic salmon, but over the last generation, there has been a continued effort to shift management as much as possible to provincial authorities through memoranda of understanding, for example. A new Atlantic salmon policy is in the works, and in the past three years there has been an attempt by government to pass a new version of the century-old Fisheries Act through Parliament.

Federal legislation regarding at-risk populations is weak. Inner Bay of Fundy Atlantic salmon runs were declared endangered in 2000. As of 2008, no recovery plan is in place.

It takes constant pressure from nongovernmental organizations, such as the Atlantic Salmon Federation, for improvements in management, and for initiatives to be considered. For example, the technology for mitigation of acid rain-impacted rivers used in Norway is needed in 54 Nova Scotia rivers. Yet, an initiative of the ASF and the Nova Scotia Salmon Association raised the funds to get a project in place, in West River-Sheet Harbour.

In Quebec, the daily catch limit for Atlantic salmon is one fish over 63 cm (25 in), two fish under 63 cm or one fish over and one under 63 cm, provided 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 seven 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.[21] 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.

Sustainable consumption

In 2010, Greenpeace International has added the Atlantic salmon to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries".[22]

See also

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. ^ Atlantic salmon. Seafood Portal.
  4. ^ a b c Klemetsen A, Amundsen P-A, Dempson JB, Jonsson B, Jonsson N, O’Connell MF, Mortensen E (2003). "Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories". Ecology of Freshwater Fish. doi:10.1034/j.1600-0633.2003.00010.x. 
  5. ^ Barton, M.: "Biology of Fishes.", pages 198-202 Thompson Brooks/Cole 2007
  6. ^ Atlantic Salmon Life Cycle Connecticut River Coordinator's Office, U.S. Fish and Wildlife Service. Updated: 13 September 2010.
  7. ^ a b . B. Dempson, C. J. Schwarz, D. G. Reddin, M. F. O’Connell, C. C. Mullins, and C. E. Bourgeois (2001). "Estimation of marine exploitation rates on Atlantic salmon (Salmo salar L.) stocks in Newfoundland, Canada". ICES Journal of Marine Science: 331–341. http://icesjms.oxfordjournals.org/content/58/1/331.full.pdf. Retrieved 2011-05-07. 
  8. ^ Mills, D. (1989). Ecology and Management of Atlantic Salmon. Springer-Verlag. 
  9. ^ a b c d Heen, K. (1993). Salmon Aquaculture. Halstead Press. 
  10. ^ a b c Sedgwick, S. (1988). Salmon Farming Handbook. Fishing News Books LTD. 
  11. ^ N. Bromage (1995). Broodstock Management and Egg and Larval Quality. Blackwell Science. 
  12. ^ R. M. J. Ginetz (May, 2002). "On the Risk of Colonization by Atlantic Salmon in BC waters" (PDF). B.C. Salmon Farmers Association. http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5065406. 
  13. ^ a b Harb, M. "Upstream Battle", Canadian Geographic Magazine, June 2008, p. 24
  14. ^ "Salmon campaigner lands top award". BBC News. 2007-04-22. http://news.bbc.co.uk/1/hi/sci/tech/6571241.stm. 
  15. ^ Atlantic Salmon Restoration Program
  16. ^ a b c P. Collen & R. J. Gibson (2001). "The general ecology of beavers (Castor spp.), as related to their influence on stream ecosystems and riparian habitats, and the subsequent effects on fish – a review" (PDF). Reviews in Fish Biology and Fisheries 10 (4): 439–461. doi:10.1023/A:1012262217012. http://www.springerlink.com/content/v48769740n817601/fulltext.pdf. 
  17. ^ Howard Park & Øystein Cock Rønning (2007). "Low potential for restraint of anadramous salmonid reproduction by beaver Castor fiber in the Numedalslågen river catchment, Norway". River Research and Applications 23 (7): 752–762. doi:10.1002/rra.1008. 
  18. ^ Barry A. Taylor, Charles MacInnis, Trevor A. Floyd (2010). "Influence of Rainfall and Beaver Dams on Upstream Movement of Spawning Atlantic Salmon in a Restored Brook in Nova Scotia, Canada". River Research and Applications: 183–193. doi:10.1002/rra.1252. 
  19. ^ Douglas B. Sigourney, Benjamin H. Letcher & Richard A. Cunjak (2006). "Influence of beaver activity on summer growth and condition of age-2 Atlantic salmon parr". Transactions of the American Fisheries Society 135 (4): 1068–1075. doi:10.1577/T05-159.1. 
  20. ^ (16 U.S.C. 1532(19)) http://www.epa.gov/EPA-SPECIES/1998/May/Day-01/e11668.htm
  21. ^ http://www.nasco.int/
  22. ^ Greenpeace International Seafood Red list

Sources

External links