MARINE SURVIVAL OF NORTH-AMERICAN AND EUROPEAN ATLANTIC SALMON - EFFECTS OF GROWTH AND ENVIRONMENT

Return rate, growth, and sea-surface temperature were analyzed to assess factors affecting Atlantic salmon (Salmo salar) post-smolt survival. Return rales from distinct North American river systems showed similar trends over a broad geographical range. A retrospective growth analysis was made by measuring intercirculi spacing patterns of the first sea-year zone of scales for fish of known stock survivorship. Observed growth patterns suggest that winter may be critical to smolt survival of North American stocks. An exploratory analysis of sea-surface temperature trends for north-eastern and northwestern portions of the Atlantic Ocean was used to characterize habitat area as defined by temperature minima and maxima. Thermally-defined habitat was then compared with Atlantic salmon production indices. Findings for North American stocks suggest that the distribution of winter habitat in the Labrador Sea and Denmark Strait was critical. For European stocks, the findings suggest reduced overall post-smolt habitat in recent years which may have resulted from cooling in the North Sea and wanning along the southern extent of nursery habitat. Our research shows the potential impact of global-scale environmental factors on Atlantic salmon production and recruitment. © 1993 Conseil International pour l’Exploration de la Mer.