Pacific salmon in Atlantic waters
A century of Pacific salmon introductions to Atlantic waters is summarized. Movements of fish were initiated in the last century, and in many countries large quantities of eggs have been introduced into rivers on both sides of the North Atlantic Ocean. The motivations for such programmes, the techniques used, and the results arc analysed for most of the documented attempts to introduce these species in the Atlantic area, with special attention being given to recent introductions (since 1950). Programmes for the introduction of Pink salmon (Oncorhynchus gorbuscha) in Newfoundland (Canada) and the Kola Peninsula (USSR) are reviewed in detail, and the use of coho salmon (Oncorhynchus kisutch) for ranching (New Hampshire, USA) and farming (Europe) is described. Pacific salmon released in Atlantic oceanic areas have shown in most cases an aptitude for survival, growth, homing, and spawning, even in areas where environmental characteristics are substantially different from their home waters. Survival rates are generally lower than in the original range and straying relatively important. However, in spite of significant returns, all attempts to establish reproducing sea-going populations have failed in the northern hemisphere. Although not developing rapidly, the use of coho salmon for aquaculture in Europe has an interesting potential. The possible causes of success or failure of the different attempts are discussed; they include an analysis of the adaptive mechanisms of populations which exist in their original habitat, and the influence of the ecological characteristics of the receiving country on the biology of the species. With the exception of the limited initial transplants of the last century, one may note that most introductions were made in areas which did not satisfy the optimum environmental requirements of the species, and where temperature regimes were probably the main limiting factors. They were also made in insufficient numbers or during a period too limited to allow sufficient time for genetic adaptation to the new environment. The consequences of these introductions on native populations of Atlantic species are also discussed. It is concluded that ecological influence on native stocks has been limited in the cases described, and the existing experimental knowledge of the interactions between species is discussed. The risk of disseminating diseases, although no severe problems appear to have been created, must be considered carefully, as do all cases of live fish transfers in or out of the natural range of the species. In conclusion, the influence of the development of aquaculture practices on wild stocks is drafted.