REPRODUCTIVE POTENTIAL AND FECUNDITY OF LAKE TROUT STRAINS IN SOUTHERN AND EASTERN WATERS OF LAKE ONTARIO, 1977-1994

We assessed the reproductive potential of various genetic strains of h atchery lake trout (Salvelinus namaycush) in southern and eastern Lake Ontario fi om indices of fecundity and indices of male abundance. Ind ices were constructed from catches of mature lake trout in gill nets d uring September 1980 to 1994 after correcting for mortality from sea l ampreys (Petromyzon marinus) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual la ke trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined f rom mature females collected in 1977 to 1981 and 1994, were nos differ ent (P > 0.05) among genetic strains. For all strains combined, fecund ity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0. 003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than f ish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. T he strain which dominated fecundity and mature male indices shifted du ring the study from Seneca Lake strain to Lake Superior strain and the n back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appear ance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994-1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.