Drifters versus residents: assessing size and age differences in Atlantic salmon (Salmo salar) fry

Abstract

Some young-of-the-year Atlantic salmon (Salmo salar) have a tendency to drift soon after emergence from the gravel, whereas others, called resident fry, set up and defend territories. Little is known about the mechanisms regulating this strong tendency to drift soon after emergence, a phenomenon that can greatly influence survival within a population. This study was carried out in the Western Brook system, Gros Morne National Park, Newfoundland, Canada. The objective was to assess differences, through biometric characteristics, between drifting and resident Atlantic salmon fry by examining both groups of fish caught simultaneously in the same riverine habitat. Resident salmon fry can be up to 4.8% longer and 20.4% heavier compared with drifting fry of similar age (measured in days since emergence). Therefore, it seems that competition, more than prior residence effect, could be part of the driving forces behind this active movement and that differences between subpopulations of Atlantic salmon fry can have major repercussions on life history patterns.