Agriculture and Environment: Salmon

Environmental Impacts of Production: Wild & Farmed Fish

Caged salmon escape virtually everywhere that salmon are farmed.

The introduction of a species to an area inevitably has unforeseen consequences. Salmon that escape from aquaculture operations can cause a wide range of impacts including competition for food and spawning habitat with both wild salmon and other species.

Escapes can interbreed and can cause genetic pollution that reduces the hardiness of wild salmon. Also, they can spread diseases that either did not previously exist in the area or were not previously a problem for wild populations.

There are large numbers of escapes. In Norway as many as 1.3 million salmon escape each year, and a full third of the salmon spawning in coastal rivers are of escaped origin. In 1997, 300,000 salmon escaped in Puget Sound in a single instance when net cages were ripped open accidentally (Weber 1997).

In 2000 an estimated 500,000 fish escaped in Scotland (Berry and Davison 2001). The year before, there were 16 reported escape incidents involving 440,000 farmed fish. Often the escapes involve much smaller numbers (only 10,000 or so might escape as a result of a single accident), but the cumulative impact on an ecosystem over the course of a year can be quite large.

There is considerable evidence that in some areas the escapes are becoming significant populations in their own right. The number of escapes in Scotland has increased more than threefold since 1998, but less than 60,000 wild salmon were caught in 1999. On the West Coast of Scotland, an estimated 22% of the "wild" catch is, in fact, escaped farmed salmon (Staniford 2001). In some of Norway's rivers, there are as many as four escaped farmed salmon for every wild one (Ellis and Associates 1996).

With an estimated half a million escapes in 2000 off the Scottish coast, farmed fish and wild fish may be interbreeding. As farmed fish are selectively bred for characteristics favourable for aquaculture, breeding between the two populations could alter the genetic makeup of wildfish and decrease their fitness to survive in the wild environment.

The significance of escapes can be demonstrated by the example of New Brunswick, Canada, where the first salmon farms were built in 1979. Within 4 years, 5% of the salmon in the nearby Magaguadavic River were escaped salmon from the farming operation. By 1995, 90% of the salmon in the river were escapes (Weber 1997). When escapes are an insignificant portion of the population in the wild, they probably pose a rather limited risk. However, when they dominate the numbers in the wild, they can very quickly become one of the major reasons for the demise of wild populations.

Farmers have every incentive to eliminate escapes because represent significant costs for buying and feeding animals. However, in some instances the releases are not accidental. Some 4 million salmon are estimated to have escaped in Chile since the industry started (Claude and Oporto 2000). In 2002 when salmon prices declined, Chilean producers actually released hundreds of thousands of salmon rather than pay to harvest them.

There is another important issue, however, when discussing the issue of escapes. This is the impact of deliberate releases from hatcheries that are intended to increase or even create salmon runs in specific river systems. For more than a century, salmon species have been released throughout the world into a wide range of river systems that did not include salmon previously. In the eastern United States, Alaskan salmon were released more than a 100 years ago in an attempt to reintroduce salmon in rivers where Atlantic salmon were extinct.

In the case of Chile, salmon were released into the wild in 1905, 1914, 1946, and 1952 in an attempt to colonise river systems thought to be suitable but with no comparable fish populations. None of the Chilean releases were successful (Claude and Oporto 2000). The implications of this for wild species are not clear.

Sea lice and other diseases spread by farmed salmon can have a devastating effect on wild salmon and other fish. Researchers found that 86% of wild migrating juvenile salmon in two Norwegian fjords died as a result of sea lice infestations that they contracted while migrating past salmon farms (Pearson and Black 2001, as cited in Berry and Davison 2001).

This contributes to the continuing decline of wild salmon, which in turn upsets the ecological balance in marine and freshwater systems. It also reduces revenue from commercial harvesting and sport fishing. The application of biological engineering to salmon has resulted in the creation and patenting of transgenic, or genetically altered salmon.

There has been pressure on the U.S. Food and Drug Administration to consider a petition to farm and sell the salon within the United States. The faring of such fish further increases the likelihood of salmon aquaculture affecting wild salmon populations as well as other organisms within the environment (Kay 2002).


Extracts from "World Agriculture & Environment" by Jason Clay - buy the book online from Island Press

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