Environmental issues with salmon

Salmon population levels are of concern in the Atlantic and in some parts of the Pacific. Salmon are typically anadromous - they rear and grow in freshwater, migrate to the ocean to reach sexual maturity, and then return to freshwater to spawn. Determining how environmental stressors and climate change will affect these fisheries is challenging due to their lives split between fresh and saltwater. Environmental variables like warming temperatures and habitat loss are detrimental to salmon abundance and survival. Other human influenced effects on salmon like overfishing and gillnets, sea lice from farm raised salmon, and competition from hatchery released salmon have negative effects as well.

Environmental pressures

The population of wild salmon declined markedly in recent decades, especially North Atlantic populations which spawn in the waters of western Europe and eastern Canada, and wild salmon in the Snake and Columbia River system in the Pacific Northwest. The decline is attributed to the following factors:

Marine variables

Sea lice

The transfer of parasites from open-net cage salmon farming, especially sea lice, has reduced numbers of wild salmon. The European Commission (2002) concluded, "The reduction of wild salmonid abundance is also linked to other factors but there is more and more scientific evidence establishing a direct link between the number of lice-infested wild fish and the presence of cages in the same estuary.", however it is impossible to verify this statement from the reference provided. It is reported that wild salmon on the west coast of Canada are being driven to extinction by sea lice from nearby salmon farms. Dr Krkosek and his research group found, with their electronic modeling predictions, two of the best runs ever recorded for wild salmon instead of the expected collapsed salmon fishery.