Spatial diffusion modelling of juvenile Atlantic salmon (Salmo salar) shows ontogenetic increase in movement rates

Abstract

For organisms with extensive ontogenetic changes in phenotypes, knowledge of how movement of individuals changes throughout life is pivotal to understanding ecological processes. Here, we study the spatial distribution of a cohort of Atlantic salmon (Salmo salar) from hatching to their third summer of juvenile life, during which they go through a fourfold change in body size. The fish originated from three distinct breeding sites, and their distribution was mapped using electrofishing throughout the river at 10 sampling periods. The spatial distribution throughout ontogeny was analysed using diffusion models. The distribution changed from three distinct nonoverlapping distributions centred on the individual breeding sites at the early first summer stage to a single continuous distribution at the end of the study. The diffusion coefficient increased throughout ontogeny, and spatial distributions were well-described using diffusion models, explaining 46%–89% of the variation. This highlights the utility of diffusion models when considering spatial habitat structure both in conservation and research.