The following dendrogram shows the similarity of the lists of species for the different types of riverbed. Rocky and silty and sandy riverbeds, due to their low species richness, were immediately distinguished from the other types of bottoms. Among the latter, riverbeds dominated by coarser sediments like a mixture of sand and gravel were distinguished from those with a finer or mixed texture. There was also a strong similarity between clayey silt bottoms and silty sand bottoms (roughly 90% of species in common), which together cover most of the riverbed in the freshwater course.

Clayey silt and silty sand bottoms were preferred by 16 species and avoided by 23 species. From five to ten species avoided gravelly sand bottoms, mixed sediments and clayey sand bottoms, while 12 to 15 species preferred these sediment types. However, sediment type did not appear to be a factor in habitat selection for many species. Sandy silt bottoms and bedrock bottoms were excluded from the analysis due to insufficient sample sizes.

Probably because of the correlation between depth and sediment type, fishes frequenting clayey silt and silty sand bottoms often have a river affinity, are more mobile and have longer spawning migrations. In contrast, fishes favouring other sediment types share different ecological characteristics.



Jacques Leclerc