Spatial distribution of Atlantic salmon (Salmo salar) breeders: among- and within-river variation and predicted consequences for offspring habitat availability

Abstract

The spatial distribution of breeders within populations may have important implications for offspring habitat availability in species where mobility of early life stages is restricted. Here we address this issue using time series of spawner distributions from eight Norwegian Atlantic salmon ( Salmo salar ) populations. Whereas spawners distribute themselves uniformly along the length of the rivers in some populations, others show a heavily skewed distribution. Linear mixed models identified pronounced and temporally consistent among-population differences in spawner distributions. Using a model of limited juvenile dispersal from nests following emergence, we show that the observed spawner distributions are predicted to result in significant proportions of rivers being inaccessible for young of the year during early life stages, and the magnitude of this effect differs among populations (e.g., ranging from 27% to 59% for dispersal distance of 250 m). Thus, assuming population regulation during early but not later juvenile stages, consistent differences in spawner distributions among populations such as those observed here may translate into differences in productivity (i.e., carrying capacity) as well as egg densities required for populations to reach their spawning targets.