Adult Biology of the River Lamprey (Lampetra ayresi) and the Pacific Lamprey (Lampetra tridentate) from the Pacific Coast of Canada

Abstract

River lamprey (Lampetra ayresi) metamorphose in late July with downstream migration occurring in the following year from May to July. Once adults enter salt water they begin to feed immediately by consuming chunks of flesh primarily from herring and young salmon. From June until September they increase in size by an estimated 11–14 cm and 12–18 g. In 1975, 667 000 lamprey were estimated to be in the Strait of Georgia resulting in the deaths of 60 000-000 juvenile fish. Between September and late winter river lamprey return to freshwater. Spawning occurs in the spring, from April to June and adults die after spawning. The length of adult life from the onset of metamorphosis until death following spawning is 2 yr. Pacific lamprey (Lampetra tridentata) begin metamorphosis in July and the known period of entry into salt water is from December until June. Feeding can commence in freshwater or salt water by mid-October. Pacific lamprey move into water deeper than 20–70 m and are present in all major fishing grounds off Canada's west coast. A relatively high incidence of lamprey attacks has been observed on sockeye and pink salmon that are aggregating in preparation to return to freshwater. The smallest mature or maturing pacific lamprey found in this study measured 16 cm and the largest measured 72 cm. Adults may spend [Formula: see text] in salt water before returning to freshwater from April to June and completing their upstream migrations by late September. Stocks that return in the spring exhibit exceptional migratory instincts often migrating considerable distances in freshwater to the uppermost regions of tributary streams before they spawn from April to July in the following year. After entry into freshwater and prior to spawning, adults shrink in length by approximately 20%. The average life span from the onset of metamorphosis until death following spawning probably is 5 yr. A nonanadromous form that appears to be a new species exists in lakes and attacks a large percentage of resident salmonids.Key words: Pacific lamprey, river lamprey, life history, fish parasites, Pacific fishes