Predatory-Phase Sea Lampreys (Petromyzon marinus) in the Great Lakes

Abstract

Incidentally caught predatory-phase sea lampreys were obtained from the commercial fisheries of the Laurentian Great Lakes, together with related catch data, in return for a reward offered to fishermen. Catches of sea lampreys per unit of fishing effort in Lake Superior generally paralleled other indices of sea lamprey abundance. Recently metamorphosed sea lampreys tended to appear early in the season in deepwater fisheries, typically those directed toward cisco (Coregonus spp.), whereas older specimens were taken more often in gear set at shallower depths during summer and fall. The proportion of male sea lampreys in the collections decreased annually between spring and fall, due apparently to a shoreward movement of the males. Large lake trout (Salvelinus namaycush) appeared to be the preferred prey of the sea lamprey. From studies of the stomach contents, sea lamprey feeding activity appeared to reach a peak in late summer or early fall, thereafter declining until the cessation of feeding in early spring. Growth rate reached a maximum in late summer or early fall. Greatest length was attained between January and March, after which a decrease in length was observed. Predatory-phase sea lampreys remained concentrated near the mouths of their parent streams if sufficient numbers of prey were present. Their distribution in the Great Lakes was related to the location of prey.Key words: sea lamprey, predation, Great Lakes fishery