Juvenile production variation in salmonids: Population dynamics, habitat, and the role of spatial relationships

Anadromous Atlantic salmon (Salmo salar) exhibit a complex life history that requires the use of habitats that span several different temporal and spatial scales. While fisheries scientists have investigated the various elements of habitat and how they affect Atlantic salmon growth and survival, these studies typically focus on requisite requirements for a single life history stage. Current advances in our understanding of salmonid populations in lotic systems indicates that ignoring the spatial positioning of different habitats and dispersal capabilities of fish between them may affect estimates of habitat quality and production of juvenile Atlantic salmon. Using the concepts of juxtaposition and interspersion, we hypothesize that discrete functional habitat units (FHU) occur within river systems and that the spatial structure of FHU affects fish production. We present a method to delineate FHU using habitat maps, fish ecology, and spatial habitat characteristics. Utilizing a simulation model, we illustrate how modeling FHU structure of spawning and rearing habitat in a river system can improve our understanding of juvenile Atlantic salmon production dynamics. The FHU concept allows a flexible approach to more comprehensive analyses of the impacts of habitat alterations, seasonal habitat shifts, and spatial ecology of salmonids at various scales.