Density, Distribution, and Movement of Nipigon Bay Fishes in Relation to a Pulp and Paper Mill Effluent

Abstract

Density of pelagic fish in accessible portions of Nipigon Bay was lower offshore, less than 100 fish/10,000 m³, and greater nearshore, less than 1800 fish/10,000 m³. Conditions at Red Rock caused intense aggregation there and caused species dominance to shift to sucker at the mill discharge from yellow perch elsewhere. Plume shape and direction did not alter the localized pattern of distribution. Two typical responses to plume concentrations were found using suckers fitted with ultrasonic transmitters. Fish released in high discharge concentrations (>15% dilution by volume) became disoriented for as much as several hours, then appeared to search for "background" conditions. Fish released in low discharge concentrations (<15%) immediately initiated an avoidance reaction. Although individuals tended to avoid areas of altered water quality, the community aggregated at Red Rock in response to, perhaps, increased production of benthic macroinvertebrates. However, telemetry indicated that residence time was short in the area of altered water quality.