e 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 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.
Overfishing at sea is generally considered the primary negative factor, 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.
Beginning around 1990, the rates of Atlantic salmon mortality at sea more than doubled. In the western Atlantic, fewer than 100,000 of the important multiple 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. In the mid-1990s, the Atlantic Salmon Federation in cooperation with partners developed sonic tracking technology, and by 2008, the salmon had 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 halfway to feeding grounds off Greenland. The problems at sea remain, leading to 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.
Possibly because of improvements in ocean feeding grounds, returns in 2008 were very positive. On the Penobscot River in Maine, returns were about 940 in 2007, and by mid-July 2008, the return was 1,938. Similar stories were reported in rivers from Newfoundland to Quebec. In 2011, more than 3,100 salmon returned to the Penobscot, the most since 1986, and nearly 200 ascended the Narraguagus River, up from the low two digits just a decade before.
Recovery[edit source | edit]
Around the North Atlantic, efforts