Biological Events during Ice Breakup in the Great Whale River (Hudson Bay)

Abstract

The physical events and changes of abundance of freshwater and marine organisms were documented daily at the mouth of the Great Whale River to a distance of about 5 km in the freshwater plume extending in Hudson Bay. For the 2-wk period before, during, and after the ice breakup, water flow and concentration of coarse (>500 μm) particulate organic matter (CPOM) decreased, while transparency and temperature increased. The Great Whale River outflow to coastal Hudson Bay for that period was estimated to contain 8.8 t of CPOM and 1021 million insects (primarily simulids). Insect drift was positively related to river flow during daylight hours, whereas night drift intensified with receding flow values. The maximum drift of freshwater–anadromous fish larvae (coregonids and Lota lota) coincided with peak flow at ice breakup. A stratified under-ice freshwater plume isolated the freshwater drift material (CPOM, insect larvae, and fish larvae) from the marine community and increased the distance at which terrigenous material was exported into Hudson Bay. During the short period of ice breakup, the Great Whale River contributes substantial amounts of material, which probably stimulates biological production on the coast of Hudson Bay.