1. Waste feed and faecal matter from farmed salmon can lead to nutrient pollution and a decrease in biodiversity around salmon cages. Toxic chemicals used to treat disease and parasites pollute the surrounding environment and harm native species.
2. Farmed salmon frequently escape pens and risk contamination of, or competition with, wild salmon stocks. Recent studies have found farmed salmon present in 87 per cent of North American rivers.
3. Disease and parasite outbreaks plague the salmon farming industry. This risks transfer to wild stocks. Farming companies often must cull these fish but sometimes they go to market and are found in local supermarkets.
Most farmed salmon raised in Canada are Atlantic salmon, including in the Pacific waters of British Columbia where the species is not native.
Farmed salmon are harvested from their open-net marine cages after about 36 months, weighing about 4.5 kilograms.
Farmed salmon generally share their cage with over 10,000 other salmon.
Farmed salmon are fed feed containing fishmeal and fish oil derived mainly from wild pelagic fish. A recent study suggests wild fish used in aqua-feed must be cut by at least half to be more sustainable.
Salmon in open-net cages face predators such as seals and marine birds that try to break through the net often causing fish to escape. Marine mammals are frequently shot or drowned, including at-risk species.