alevin which, within around 24 hours, will absorb the yolk sac and become a fry
Hybridization[edit source | edit]
When in shared breeding habitats, Atlantic salmon will hybridize with brown trout (Salmo trutta). 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 they were not significantly heterogeneous 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.
Aquaculture[edit source | edit]
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 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, Ireland, Faroe Islands, Russia and Tasmania in Australia. Sport fishing communities, mainly from Iceland and Scandinavia, have joined in the North Atlantic Salmon Fund to buy away commercial quotas in an effort to save the wild species of Salmo salar.
Process[edit source | edit]
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 fresh water. 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 USA, or parts of Europe.
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.
Controversy[edit source | edit]
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 escape is no longer considered a major concern. Evidence of Atlantic salmon surviving and establishing wild populations in the Pacific is lacking. 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 BC 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. 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.
Human impact[edit source | edit]
Human activities have heavily damaged salmon populations across their range. The major impacts were from overfishing and habitat change, and the new threat from competitive farmed fish. 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. When dams were constructed on the Oswego River, their spawning areas were cut off and they went extinct locally.
In the 1950s, salmon from rivers in the US and Canada, as well as from Europe, were discovered to gather in the sea around Green