Swimming performance of Anadromous Atlantic salmon, Salmo salar L., during their spawning migration in the Exploits River, Newfoundland, Canada

Swimming performance, muscle activity patterns and plasma non-esterified fatty acid profiles were examined in wild Atlantic salmon (Salmo salar L.) during their upstream spawning migration and downstream post-spawning migrations. These studies were conducted on the Exploits River, Newfoundland, Canada between June of 1994 and October of 1996. Significant reductions in sustained and prolonged swimming performances were observed during the upstream migration of adult Atlantic salmon. Associated with the reductions in swimming performance, spawning Atlantic salmon demonstrated higher muscle activity indices for any given swimming speed than non-spawning individuals. The greatest loss of swimming performance, and change in muscle activity was observed for females just prior to spawning. Both swimming performance and muscle activity indices were correlated with observed changes in temperature and body cross sectional area. The change in cross sectional area was more pronounced among females and was related to the final stages of ovarian maturation. Sustained, prolonged and burst swimming performance of Atlantic salmon kelts were significantly lower than those of upstream migrating individuals. Smolts were also investigated. Smolts were capable of swimming significantly faster than adults when swimming speeds were expressed relative to body length. Total plasma non-esterified fatty acid (NEFA) levels declined significantly between freshwater entrance and spawning, and continued to decline during the post-spawning period. Plasma NEFA levels were significantly higher for females but declined to a greater extent during the upstream migration. The rapid decline in plasma NEFAs among females coincided with the largest increase in their gonadosomatic indices. Differences in the circulating levels of polyunsaturated and saturated fatty acids became evident in males and females just prior to spawning. At spawning, males and females possessed similar amounts of all plasma NEFAs and these did not changes during the post-spawning period. Decreases in temperature, changes in body morphology and depletion of lipid (i.e. plasma NEFAs) were observed and recorded during the freshwater migration of Atlantic salmon. Collectively, these factors may have resulted in the pronounced changes in swimming capabilities and muscle activity patterns observed in migrating salmon. The observed changes in the swimming performance and the significant loss of plasma NEFAs suggest that Atlantic salmon may become more susceptible to disturbances in their migrations as they approach sexual maturity and prepare to spawn.