Research Document 1998/162

Ecological and behavioural interactions between farmed and wild Atlantic salmon: consequences for wild salmon in the Maritimes region

By G. Lacroix and I. Fleming

Abstract

The concentration of hatcheries and sea cages for Atlantic salmon farming in several areas of the Maritime Provinces introduces the probability that ecological interactions between farmed and wild Atlantic salmon will occur. Farmed salmon escape as fry, parr and smolts into fresh water and as smolts, post-smolts and adults in coastal marine areas, and they can move from one habitat to the other and interact directly or indirectly with wild salmon. In fresh water, the entry of escaped farmed spawners can influence natural migration and spawning, and behavioural interactions can affect mating selectivity and interbreeding that control genetic interactions and population performance. Between the fry and smolt stages, competition for food and space can increase with the intoduction of large numbers of conspecific organisms with a distinct developmental and size advantage. In addition, predator-prey relationships can potentially be altered by flooding streams with farmed fry, parr and smolts. These interactions would lead to changes in productibity of native salmon populations through processes affecting growth and survival. In the marine environment, the migratory behaviour of post-smolts and adults through areas with many closely spaced cage sites and high densities of farmed fish could be altered and wild fish could fall prey to the predators around cage sites. Exposure to many cage sites also would increase the probability of disease and parasite transmission to wild fish. These interactions could increase the marine mortality rate of wild salmon from local and distant stocks that migrated through cage site areas. The apparently large number of escaped farmed salmon remaining in the marine in the marine environment also increases the probability of dispersal and interaction with wild salmon stocks outside of aquaculture areas. Although interactions between farmed and wild salmon have been shown to occur, few of these have been investigated in the Maritime Provinces and their impacts on wild salmon remain unknown.

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