By Asbjørn Bergheim*
Wild stocks are in a weakened state and the rapidly growing farming of salmon is often blamed for this worrying situation. Undoubtedly, interactions between salmon aquaculture and wild salmon stocks are a part of the problem but the degree of impact from the industry is difficult to estimate.
About 2,500 salmon rivers flow into the North Atlantic (www.nasco.int). The annual catches of salmon at sea peaked in the mid-1970s at about 12,000 tons, but the catches have declined markedly to about 1,500 tons in recent years. Part of the reason for reduced catches is due to the introduction of restrictive management measures in fisheries (www.nasco.int), while reduced abundance of salmon is another obvious major reason. Also, monitoring of salmon stocks in rivers indicates that the marine survival has declined dramatically.
The International Council for the Exploration of the Sea, or ICES (www.ices.dk) is the world’s leading scientific organization concerning marine ecosystems. The organization annually provides reliable estimates of the state of Atlantic salmon. Both in Canada and Europe, the returning number of salmon from sea to their home rivers has declined (Figure 2 a, b) concurrently with the reduced catches at sea. Not least, the falling percentage of large salmon returning after two or more winters at sea clearly indicates this reduced marine survival.
According to The Atlantic Salmon Trust (www.atlanticsalmontrust.org), the species is “in danger of extinction”, especially in its southern range: Portuguese rivers no longer have salmon and the river populations in NW Spain and in southern France are on the edge, despite heroic efforts by the fishery managers. On the other side of the Atlantic Ocean, the situation is unfortunately much the same where 40,000 annual salmon runs in the rivers of the Bay of Fundy in the 1970’s have declined to about 200 ascending salmon at present. However, the picture is a mixed one. In 2014, the rivers of Russia’s Kola Peninsula had notable high runs and catches of salmon and, for example, the Irish river Slaney had its best spring returns for thirty years.
The estimated number of salmon caught by anglers in Norwegian rivers in 2015 was totally 132,000 individuals, up 10% compared with the average number over the last decade (www.kyst.no). River fishing in Norway is strictly regulated and subject to maximum catch quotas. All salmon angled in rivers that are not incorporated in the quota regulations have to be released. Some 25,000 salmon or 19% of the total 2015 catch were reported released to contribute to maintaining the rivers’ strains. Norway’s salmon strains are considered vigorous despite the fact that eleven strains out of 110 are critically endangered or extinct (www.nina.no).
A main cause of the present high return rate of spawners in Norwegian rivers is supposed to be the low number of sea lice in the fjords during spring 2013 at the time of smolt migration (www.imr.no). The lice treatment attempts at the cage farms were successfully performed that year and the number of returning large salmon in 2016, representing this generation, will probably exceed the average number for these highly desired fish.
ICES has classified the following factors that can affect the mortality of salmon at sea: Growth, food and competition; Salmon fisheries; By-catches in pelagic fisheries; Freshwater influence; Marine environment and pollution; Marine parasites and diseases; and Marine predation. Salmon aquaculture is considered a potential threat to the wild stocks in the inshore zone. In an international symposium held ten years ago (Oct. 2005), representatives from the farming industry and experts on wild stocks stated that “the industry’s future success requires that the product is perceived to be safe and healthy, that it is not associated with degradation of the natural environment, and that the industry is perceived as open, transparent, and willing to focus on welfare issues and environmentally sustainable practices” (www.icesjms.oxfordjournals.org).
Unlike other major salmon farming regions, Chile does not have native wild salmon populations. The species that are dominating the salmon industry, Atlantic salmon and coho, are introduced from their endemic regions and the disease and parasite problems affecting the industry thus represent no significant impact on wild fish populations.
Dr. AsbjØrn Bergheim is a senior researcher in the Dept. of Marine Environment at the International Research Institute of Stavanger. His fields of interest within aquaculture are primarily water quality vs. technology and management in tanks, cages and ponds, among others.