RELATIONSHIP BETWEEN COD FISHERY ACTIVITIES AND THE POPULATION OF HERRING-GULLS ON THE NORTH SHORE OF THE GULF OF ST-LAWRENCE, QUEBEC, CANADA

The history of herring gull (Larus argentatus) populations nesting alo ng the North Shore of the Gulf of St Lawrence and the commercial fishi ng activities there are closely related. Coastal cod (Gadus morhua) su pply the main fishery in this part of the Gulf and traditionally have resulted in significant amounts of fish offal being discarded at sea a nd in fishing ports. Using commercial catch data of cod landings, and information from herring gull surveys conducted in the migratory bird sanctuaries on the North Shore from 1925 to 1993, the relationship bet ween the cod fishery and herring gull populations was investigated. Be tween 1925 and 1975 the fisheries harvested a mean of 5 234 t of cod a nnually, with high and low catches of 11 000 and 1 700 t, respectively . During the same period, the herring gull population in the sanctuari es increased from 650 to 8000 pairs. After 1975, and until 1993, the a nnual mean harvest was 5771 t peaking in 1983 at 11 500 t. There was t hen a steady decline until a complete fishery collapse in 1993. During the same period, the herring gull population increased from 8 000 pai rs in 1975 to 14 000 pairs in 1988, but then dropped dramatically in m ost sanctuaries and was estimated at only 3000 pairs in 1993. This gen eral decline of gulls appears to be related to the decrease in commerc ial fishing activities in the region, but not uniformly so. (C) 1997 I nternational Council for the Exploration of the Sea.