A study of terrestrial and aerial macroinvertebrates on river banks and their contribution to drifting fauna and salmonid diets in a Scottish catchment

Macroinvertebrates of terrestrial and aerial origin were examined on the river banks, in the drifting community and in the stomach contents of salmonids at seven stream sites within the river Nethy catchment in Scotland over a 12 month period. Differences between sites (which varied from moorland to forest), had some influence on the taxonomic composition and diversity of riparian macroinvertebrates but not on the proportion of terrestrial and aerial organisms in the drift or in salmonid guts. The abundances of terrestrial and aerial organisms collected on the river banks and in the drift were not related to the combination of riparian vegetation and altitude. The abundance on the river banks of terrestrial and aerial macroinvertebrates, particularly those possessing wings, varied seasonally and was positively correlated with temperature. Terrestrial and aerial prey contributed up to 86% of the salmonid diet. Organisms most abundant on the river banks were not always the predominant organisms in the drift or those selected by salmonids. This study concludes that it is necessary to examine the riparian and benthic macroinvertebrates (the original prey sources) and the drift (as the actual source of salmonid forays) directly to elucidate salmonid trophic pathways.