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

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.