Upstream Movements of the Benthic Invertebrates in the Speed River, Ontario

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Abstract
Investigation of the benthic fauna of the Speed River, Ontario, was carried out from June 1966 to September 1967. Upstream movement of substantial numbers of invertebrates was detected using solid-walled traps with induced current, and Terylene net traps. The mechanism for this was largely positive rheotaxis, but positive skototaxis and the release of phototactic control probably governed the distance covered. During the winter, statistically greater movement occurred in areas adjacent to the banks than in midstream, but in summer the midstream areas contributed most of the migrants. Artificially darkening the traps increased the biomass moving into them. Movements upstream counteracted 6.5% of downstream drift by numbers and 4% by weight, but no comparison of relative distance travelled was made. The upstream movement was of sufficient quantity and species diversity to account for recolonization of dried-out or erosion-denuded areas.