PREDATION BY SEA LAMPREY (PETROMYZON-MARINUS) ON LAKE TROUT (SALVELINUS-NAMAYCUSH) IN SOUTHERN LAKE ONTARIO, 1982-1992

Dead lake trout (Salvelinus namaycush) killed by sea lamprey (Petromyz on marinus) were collected from the bottom of Lake Ontario using botto m trawls. The number of dead lake trout per hectare could be predicted from the number of type A-1 sea lamprey marks observed on live fish i n September gillnet surveys (r(2) = 0.60, P < 0.01) but not from the s um of marks of types A-1, A-2, and A-3 combined. Sea lamprey selective ly attacked and killed the largest lake trout. The lengths and ages of live fish with A-1 marks increased as the population of longer, older lake trout in the lake increased, and the length distributions of fis h killed by sea lamprey were not different (P > 0.05) from those of li ve fish with A-1 marks in 5 of 6 years where comparisons could be made . Compared with Lake Superior strain lake trout, Seneca Lake strain fi sh were only 0.41 times as likely to be attacked by sea lamprey and we re less likely to die from an attack (both differences P < 0.05). Cons ervative estimates of the numbers of lake trout killed by sea lamprey in southern Lake Ontario from October to mid-November ranged from 17 0 00 in 1988 to 121 000 in 1984.