SOME FACTORS WHICH INFLUENCE THE SURVIVAL OF HATCHERY ATLANTIC SALMON (SALMO-SALAR) SMOLTS UTILIZED FOR ENHANCEMENT PURPOSES

Sixty-nine groups of 2+ Atlantic salmon smolts and 27 groups of 1+ smolts produced at the Mactaquac Hatchery were marked with modified Carlin tags and released in the Saint John River, N.B., during the 1973-1988 period. During the same period, 35 groups of tagged 1+ smolts produced at the Mersey Hatchery were released in the LaHave River, N.S. The numbers of tagged adult salmon subsequently recovered in distant and local commercial fisheries, in Native food fisheries, by anglers and at collection facilities operated by the Department of Fisheries and Oceans provided a measure of the survival of the various smolt groups. Neither release date nor river discharge at time of release significantly influenced the survival of tagged smolts. Survival rates for groups of smolts released in the LaHave River fluctuated from year to year in a pattern similar to that observed for groups of smolts released in the Saint John River. The year-to-year fluctuation in the survival of the LaHave and Saint John smolts was correlated and considered to reflect changing conditions at sea. Stepwise multiple regression analysis indicated that 44-68% of the variation in the survival rate of the 1+ and 2+ smolts was attributable to smolt weight at time of release, smolt quality (as determined by an index) and to sea conditions during a particular year. The results of the analysis provide rationale for modifying hatchery rearing practices and facilities to increase mean smolt weight and to improve smolt quality.