Atlantic salmon

The Atlantic salmon was given its scientific binomial name by Swedish zoologist and taxonomist Carl Linnaeus in 1758. The name, Salmo salar, derives from the Latin salmo, meaning salmon, and salar, meaning leaper, according to M. Barton, but more likely meaning "resident of salt water" . Lewis and Short's Latin Dictionary (Clarendon Press, Oxford, 1879) translates salar as a kind of trout from its use in the Idylls of the poet Ausonius (4th century CE). Later, the differently coloured smolts were found to be the same species. Other names used for the Atlantic salmon are: bay salmon, black salmon, caplin-scull salmon, fiddler, sebago salmon, silver salmon, outside salmon and winnish. At different points in their maturation and life cycle, they are known as parr, smolt, grilse, grilt, kelt, slink, and spring salmon. Atlantic salmon that do not journey to sea are known as landlocked salmon. ==Description==

, showing the kype characteristic of breeding males Atlantic salmon are the largest species in the genus Salmo. After two years at sea, the fish average in length and in weight. Specimens that spend four or more winters feeding at sea, or are repeat spawners, can be much larger. An Atlantic salmon netted in 1960 in Scotland, in the estuary of the river Hope, weighed , the heaviest recorded in all available literature. Another netted in 1925 in Norway measured in length, the longest Atlantic salmon on record. The colour of young Atlantic salmon does not resemble the adult stage. While they live in fresh water, they have blue and red spots. At maturity, they take on a silver-blue sheen. The easiest way of identifying them as an adult is by the black spots predominantly above the lateral line, though the caudal fin is usually unspotted. When they reproduce, males take on a slight green or red colour. The salmon has a fusiform body, and well-developed teeth. All fins, except the adipose fin, are bordered with black. ==Distribution and habitat==

, in Norway The natural breeding grounds of Atlantic salmon are rivers in Europe and the northeastern coast of North America. In Europe, Atlantic salmon are still found as far south as Spain, and as far northeast as the Pechora River in Russia. Atlantic salmon have spread north to colonise Svalbard (78°N) from 2002–2006 onward, due to the warming of the climate there. Because of sport-fishing, some of the species' southern populations in northern Spain are growing smaller. The species distribution is easily influenced by changes in freshwater habitat and climate. Atlantic salmon are a cold-water fish species and are particularly sensitive to changes in water temperature. The Housatonic River, and its Naugatuck River tributary, hosted the southernmost Atlantic salmon spawning runs in the United States. However, there is a 1609 account by Henry Hudson that Atlantic salmon once ran up the Hudson River. In addition, fish scale evidence dating to 10,000 years BP places Atlantic salmon in a coastal New Jersey pond. Two publications from 1988 and 1996 questioned the notion that Atlantic salmon were prehistorically plentiful in New England, when the climate was warmer as it is now. This argument was primarily based on a paucity of bone data in archaeological sites relative to other fish species, and the assertion that historical claims of abundance may have been exaggerated. This argument was later challenged in another paper which claimed that lack of archaeological bone fragments could be explained by salmon bones being rare at sites that still have large salmon runs and that salmonid bones in general are poorly recovered relative to other fish species. Atlantic salmon populations were significantly reduced in the United States following European settlement. The fur trade, timber harvesting, dams and mills and agriculture degraded freshwater habitats and lowered the carrying capacity of most North American streams. Beaver populations were trapped to near-extinction by 1800, and log drives and clear-cutting further exacerbated stream erosion and habitat loss. As timber and fur gave way to agriculture, freshwater Atlantic salmon habitat was further compromised. According to historian D.W. Dunfield (1985) "over half of the historical Atlantic salmon runs had been lost in North America by 1850". As early as 1798, a bill for the preservation of Atlantic Salmon was introduced in Canadian Parliament, to protect populations in Lake Ontario. In the Gulf Region of Nova Scotia it was reported that 31 of the 33 Atlantic salmon streams were blocked off by lumber dams, leading to the extirpation of early-run fish in many watersheds. The inshore Atlantic salmon fishery became a major export of the New World, with major fishing operations establishing along the shores of major river systems. The southernmost populations were the first to disappear. Young salmon spend one to four years in their natal river. When they are large enough (c. ), they smoltify, changing camouflage from stream-adapted with large, gray spots to sea-adapted with shiny sides. They also undergo some endocrinological changes to adapt to osmotic differences between fresh water and seawater habitat. When smoltification is complete, the parr (young fish) now begin to swim with the current instead of against it. With this behavioural change, the fish are now referred to as smolt. When the smolt reach the sea, they follow sea surface currents and feed on plankton or fry from other fish species such as herring. During their time at sea, they can sense the change in the Earth magnetic field through iron in their lateral line. When they have had a year of good growth, they will move to the sea surface currents that transport them back to their natal river. It is a major misconception that salmon swim thousands of kilometres at sea; instead they surf through sea surface currents. It is possible they find their natal river by smell, although this is not confirmed; only 5% of Atlantic salmon go up the wrong river. The range of an individual Atlantic salmon can thus be the river where they are born and the sea surface currents that are connected to that river in a circular path. Wild salmon continued to disappear from many rivers during the twentieth century due to overfishing and habitat change. ==Ecology==

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. Plankton such as euphausiids are important food for pre-grilse but amphipods and decapods are also consumed. The most commonly eaten foods include caddisflies, blackflies, mayflies, stoneflies, Other fish consumed include herring, alewives, smelts, scomberids, sand lance, and small cod. In North America, the landlocked strains are frequently known as ouananiche. Freshwater phase The freshwater phases of Atlantic salmon vary between two and eight 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, and in Ungava Bay, northern Quebec, smolts as old as eight years have been encountered. Migration and spawning exact an enormous physiological toll on individuals, such that repeat spawners are the exception rather than the norm. Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern Spain. The proportions of hybrids in samples of salmon ranged from 0 to 7-7% but these proportions were not significantly homogeneous among locations, resulting in a mean hybridization rate of 2-3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in Europe. 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 salmon upstream of the dams suggests they are penetrated by parr. Downstream migration of Atlantic salmon smolts was similarly unaffected by beaver dams, even in periods of low flows. 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. The importance of winter habitat to salmonids afforded by beaver ponds may be especially important in streams of northerly latitudes without deep pools where ice cover makes contact with the bottom of shallow streams. ==Relationship to humans==

Atlantic salmon is a popular fish for human consumption European fishermen gillnetted for Atlantic salmon in rivers using hand-made nets for many centuries and gillnetting was also used in early colonial America. In its natal streams, Atlantic salmon are considered prized recreational fish, pursued by fly anglers during its annual runs. At one time, the species supported an important commercial fishery, but having become endangered throughout its range globally, wild-caught Atlantic salmon are now virtually absent from the market. Instead, nearly all are from aquaculture farms, predominantly in Norway, Chile, Canada, the UK, Ireland, Faroe Islands, Russia and Tasmania in Australia. on farmed Atlantic salmon Adult male and female fish are anaesthetised; their eggs and sperm are "stripped" after the fish are cleaned and cloth dried. Sperm and eggs are mixed, washed, and placed into freshwater. Adults recover in flowing, clean, well-aerated water. Some researchers have even studied cryopreservation of their eggs. 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 US, or parts of Europe. Advancements in cage technologies have allowed for reduction in fish escapes, improvement in growing conditions, and maximization of aquaculture production volume per unit area of growing space. A study in 2000 demonstrated that the genes of farmed Atlantic salmon intrude wild populations mainly through wild males breeding with farmed females, though farmed specimens showed reduced capacity for breeding success overall compared to their wild counterparts. Further study in 2018 discovered extensive cross-breeding of wild and farmed Atlantic salmon in the Northwest Atlantic, showing that 27.1% of fish in 17 out of 18 rivers examined are artificially stocked or hybrids. Farming of Atlantic salmon in open cages at sea has also been linked, at least in part, to a decline in wild stocks attributed to the passing of parasites from farmed to wild individuals. On the west coast of the United States and Canada, aquaculturists are generally under scrutiny to ensure that non-native Atlantic salmon cannot escape from their open-net pens, however occasional incidents of escape have been documented. During one incident in 2017, for example, up to 300,000 potentially invasive Atlantic salmon escaped a farm among the San Juan Islands in Puget Sound, Washington. Washington went on in 2019 to implement a gradual phase out of salmon farming to be completed by 2025. Despite being the source of considerable controversy, the likelihood of escaped Atlantic salmon establishing an invasive presence in the Pacific Northwest is considered minimal, largely because a number of 20th century efforts aimed at deliberately introducing them to the region were ultimately unsuccessful. From 1905 until 1935, for example, in excess of 8.6 million Atlantic salmon of various life stages (predominantly advanced fry) were intentionally introduced to more than 60 individual British Columbia lakes and streams. Historical records indicate, in a few instances, mature sea-run Atlantic salmon were captured in the Cowichan River; however, a self-sustaining population never materialized. Similarly unsuccessful results were realized after deliberate attempts at introduction by Washington as late as the 1980s. Consequently, environmental assessments by the US National Marine Fisheries Service (NMFS), the Washington Department of Fish and Wildlife and the BC Environmental Assessment Office have concluded the potential risk of Atlantic salmon colonization in the Pacific Northwest is low. Future prospects A study of Næve et al. (2022) estimated the impact of 50 years of genetic selection and tried to predict the impact it could have until 2050. In order to do this, a common garden experiment was used to model and simulate past and future effects for 11 generations of genetic selection of increased growth rate in Atlantic salmon. To model the contribution that breeding has made in the industry from generation 0 (harvested in 1975– 1978) to generation 11 (harvested in 2017 – 2019), and to simulate growth until 2050 (generation 24), the Norwegian salmon aquaculture production between 2016 and 2019 was used as a base case. The simulation of the expected growth until 2050 (generation 24) gave five different scenarios : Historical (H1), Forecast 1 (F1), Forecast 2 (F2), Forecast 3 (F3) and Forecast 4 (F4). Changes in thermal growth coefficient (TGC) per generation were used in the model to simulate the differences in the five scenarios. The genetic data, H1, and the most conservative forecast scenario, F1, simulate what can be expected in 2050 if the trend from generation 0 through 11 is maintained. The following forecast scenarios assume a greater increase in genetic growth with a larger increase in the TGC in the generations to come. In the next two generations, more advanced selection methods such as marker assisted selection (from generation 10) and genomic selection (from generation 11) were implemented. This resulted in increased gain in selection for growth and simulated F2 and F3. The most progressive scenario, F4, aimed at exploring the effect in the industry when the full genetic potential is utilized. This assumes a further development of advanced techniques in the years to come. The authors of the article found that the daily yield of the biomass increased with increasing generations in the historic and forecast scenarios. Further, the production time in seawater to reach the harvest weight of 5100 g is expected to be reduced by 53% in 2050. When production time can be reduced, this will also reduce e.g. time at risk of diseases. In the most progressive scenario, mortality in seawater was expected to be reduced by up to 50%. Further, the authors found that production per license can increase by up to 121%. Additionally, 77% of the new volume needed to achieve five million tonnes in 2050, may be provided by genomic selection. However, one should keep in mind that this article was published by the firm Aquagen, and can possibly be biased and too optimistic. ==Conservation==

of Quebec as recreation., Sweden shows a Norwegian salmon. The IUCN rates Salmo salar with a conservation status of "near threatened". Human activities have impacted salmon populations across parts of its range. The major threats are from overfishing and habitat change. In the 1950s, salmon from rivers in the United States and Canada, as well as from Europe, were discovered to gather in the sea around Greenland and the Faroe Islands. A commercial fishing industry was established, taking salmon using 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.Beginning around 1990, the rates of Atlantic salmon mortality at sea more than doubled in the western Atlantic. Rivers of the coast of Maine, southern New Brunswick and much of mainland Nova Scotia saw runs drop precipitously, and even disappear. An international effort to study the increased mortality rate was organized by the North Atlantic Salmon Conservation Organization. In 2007 at least one sport fishing organization from Iceland and Scandinavia blamed less fish caught by recreational anglers on overfishing at sea, and thus created the North Atlantic Salmon Fund to buy commercial quotas in the Atlantic from commercial fishermen in an effort to preserve wild Salmo salar stocks. Recreational fishing of stocked, landlocked Atlantic salmon is now authorized in much of the US and Canada where it occurs in large numbers, but this is subject to regulations in many states or provinces which are designed to maintain the continuity of the species. Strict catch limits, catch and release practices and forced fly fishing are examples of those regulations. However, catch and release angling can be an additional stressor on Atlantic salmon populations, especially when its impacts are combined with the existing pressures of climate change, overfishing, and predation. in 2006, which is one of the largest freshwater conservation programs in North America. It has since stocked Lake Ontario and surrounding tributaries with upwards of 6,000,000 young Atlantic salmon, with efforts growing each year. 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 techniques 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. Lake Champlain now has Atlantic salmon. The Atlantic Salmon Federation is involved in restoration efforts along the eastern United States and Canada, where their projects are focused on removing barriers to fish passage and eradicating invasive species. Recent documented successes in the reintroduction of Atlantic salmon include the following: • In October 2007, salmon were video-recorded running in Toronto's Humber River by the Old Mill. • In November 2015, salmon nests were observed in Connecticut in the Farmington River, a tributary of the Connecticut River where Atlantic salmon had not been observed spawning since "probably the Revolutionary War". However, both state and federal experts indicated that this find likely represented a dwindling wave of returning stocked fish from massive salmon restoration efforts that had concluded years earlier in 2012. Significant doubt was cast on fish returning to spawn in meaningful numbers after 2017, when the last generation of stocked salmon would return. • In April 2024, as a result of river restoration it was reported that the Atlantic salmon are once again spawning in the upper waters of the River Derwent in the heart of the United Kingdom for the first time in 100 years. NASCO The North Atlantic Salmon Conservation Organization is an international council made up of Canada, the European Union, Iceland, Norway, the Russian Federation, the United Kingdom, and the United States, with its headquarters in Edinburgh. 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. In December 2021, NASCO published an updated interactive map of their Rivers Database, showing the stock status of wild Atlantic salmon populations across the species range. ==Legislation==

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 on 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 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, the 32 boards, which by then were integrated into regional river authorities, were reduced to 10 regional water authorities (RWAs). Although only the Northumbrian Water Authority, Welsh National Water Development Authority, Northwest Water Authority and Southwest Water Authority had significant salmon populations, all ten also regulated and conserved trout and freshwater eel fisheries The Salmon and Freshwater Fisheries Act was passed in 1975. Among other things, it regulated fishing licenses, seasons, and size limits, and banned obstructing the salmon's migratory paths. In 1318, King Robert I enacted legislation setting a minimum size for cruives, "so that no fry of fish are impeded from ascending and descending..." Laws on catching fish upon royal lands were frequently updated, demonstrating their importance. The export of salmon was economically important in Aberdeen; beginning in the 15th century, the fish could be preserved through salting and barreling, allowing them to be exported abroad, including as far away as the Baltic. The volume of the early Scottish salmon trade is impossible to determine, since surviving custom records date only from the 1420 onward, and since Aberdeen burgesses enjoyed an exemption on salmon customs until the 1530s. 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. 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. Canada The federal government has prime responsibility for protecting the Atlantic salmon, but over the last generation, effort has continued 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, the government has attempted 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. A recovery and action plan is in place. Nongovernmental organizations, such as the Atlantic Salmon Federation, constantly demand for improvements in management, and for initiatives to be considered. For example, the ASF and the Nova Scotia Salmon Association desire the use of technology for mitigation of acid rain-affected rivers such as used in Norway is in 54 Nova Scotia rivers and managed to raise the funds to get a project in place in one river. In Quebec, the daily catch limit for Atlantic salmon is dependent on the individual river. Some rivers are strictly catch and release with a limit of 3 released fish. Each catch must be declared. Some rivers allow you to keep between 1 or 2 grilse (30 cm to 63 cm), while some of the more prolific rivers (mainly on the north coast) will allow you to keep 1 salmon over 63 cm. The annual catch limit is 4 Atlantic salmon of small size and only 1 of those may be bigger than 63 cm. In Lake Ontario, the historic populations of Atlantic salmon became extinct, and cross-national efforts have been under way to reintroduce the species, with some areas already having restocked naturally reproducing populations. ==See also==