Oyster Mortalities in the Upper Rappahannock River and in the Virginia Tributaries of the Lower Potomac - Their Association with High River Discharge and Low Salinity

摘要

This report was prepared at the request of a majority of the oyster growers in the Virginia tributaries of the lower Potomac River and in the upper Rappahannock River. Growers in these two areas began experiencing excessive losses during the 1977-78 and 1978-79 growing seasons; losses during the winter and spring of 1980 were especially severe. Salinity data, available for the period 1970 through 1980 demonstrates the persistence of salinities at levels which would inhibit growth and feeding and which could cause excessive mortalities. The annual mean river discharge for the Rappahannock River at the gaging station near Fredricksburg demonstrates that the volume of freshwater entering the Rappahannock during 1979 was greater than any year previously recorded. This unusally high rate of discharge is responsible for the low salinities and no doubt for the heavy oyser mortalities reported.