Agriculture and Environment: Salmon

Environmental Impacts of Production: Impact on Predators

Salmon in net cages attract predators such as seals, river otters, sharks, kingfishers, eagles, cormorants, and great blue herons.

The effect on these animals of consuming salmon that have antibiotics and other chemicals in them is not known.


Nor is it clear how greatly they have been impacted by various methods salmon farmers employ to keep them away. One of the methods is simply to kill them. Seals, for example, can be shot by salmon farmers in British Columbia, though the farmers must obtain permits to do so.

350 seals shot each year in Scotland alone
It is estimated that at least 500 are shot by salmon farmers each year in British Columbia, where harbour seals are estimated to cost the industry $10 million a year (Weber 1997). In Scotland the industry estimates that 350 seals are shot each year, while environmentalists put the figure at 5,000 (Weber 1997).

Close to 6,000 sea lions killed in Chile
From the 1980s to the mid-1990s, some 5,000 to 6,000 sea lions were killed in Chile by salmon farmers. In addition, an unknown number of dolphins and even an occasional minke whale were killed (Claude and Oporto 2000).

According to one study (Brunetti et al. 1998, as cited in Claude and Oporto 2000), sea lions cost the Chilean salmon industry about $21 million in damage annually (in direct costs as well as the cost of security, etc.). This amount was some 3% of sales.

Farmers also use predator nets, or nets above and around the salmon cage, to prevent predators from getting too close to the cage. Netting used to exclude marine mammals and birds can entangle and drown animals. Some producers leave the dead animals there as a way to scare away others.

Acoustic devices to drive away other species
Acoustic devices that emit a high-pitched sound can be used to scare away seals and sea lions. In some instances these devices have been so successful that they have also caused the withdrawal of resident populations of harbour porpoise and whales.

The extent of the impact of any of these methods on bird and mammal populations is unclear, but potentially they could have a great impact, especially in areas where salmon farms are highly concentrated.

Credits

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

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