Mass Mortality of Estuarine Fauna at Bideford, P.E.I., Associated with Abnormally Low Salinities

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Abstract
Spring thaw discharges large quantities of fresh water into estuaries in the Gulf of St. Lawrence. Surface freshwater layers of 1 m are normal but deeper water usually remains at close to full salinity. Shallow-water animals are adapted to withstand low salinities but those from deeper water are not. In May 1967 an up-estuary gale caused the buildup of an extraordinarily deep freshwater layer in Bideford River, P.E.I.; salinities at 3 m fell to less than 1‰. Scuba surveys after this phenomenon revealed extensive mortalities in a variety of species. Several of these species often occur in low-salinity areas and it is suggested that mortalities resulted from the very rapid salinity change combined with warming water temperatures.