DYNAMICS OF REPRODUCTION BY HATCHERY-ORIGIN LAKE TROUT (SALVELINUS-NAMAYCUSH) AT STONY ISLAND REEF, LAKE-ONTARIO

Natural recruitment from hatchery-origin lake trout in the Great Lakes has been minimal, except in Lake Superior and a few limited areas in Lake Huron. Quantitative studies of survival between egg deposition an d fry emergence were conducted on a spawning reef in the eastern basin of Lake Ontario to determine variables associated with poor reproduct ion of hatchery-origin lake trout. Thirty to 90 mesh bags were buried in the substrate of Stony Island Reef in 1990, 1991, and 1992 to colle ct eggs and fry. Bags were retrieved on three dates over the six month period between the end of spawning and fry emergence. Mean egg abunda nce in the substrate increased significantly (P < 0.01) from 700 m(-2) in 1990 to 3,572 m(-2) In 1991 and 3,355 m(-2) in 1992. Change in egg abundance probably resulted from an increase in the proportion of Sen eca strain spawners, rather than an increase in the total number of ad mits in the eastern basin. Mean embryo survival from spawning to late November or early December was 45% (range, 27-57%), approximately 7.5% (range, 7.4-7.5%) to mid-April, and about 3% (range, 1.8-3.9%) to the time of emergence in mid-May. Much of the early mortality of fertiliz ed eggs was probably due to physical shock caused by water currents du ring storms. Mortality later in development was caused by predation an d possibly poor incubation quality of substrate along the base of the reef due to sedimentation. A life history model for lake trout in Lake Ontario was developed and parameters set with the levels of fertiliza tion and egg-to-fry survival rate estimated in this study. Other param eters were estimated from stocking rates and previous studies. Model o utput indicated that the current lake trout population has the potenti al to produce over 1.2 million age-1 fish annually. No evidence exists for this level of recruitment in Lake Ontario. Natural recruitment ma y be limited by a low proportion of eggs incubating in suitable substr ate and/or low survival of fry to age-1. These problems could be due t o a combination of 1) a limited amount of spawning habitat, 2) ineptit ude of some strains to locate ol recognize spawning habitat, 3) diseas e-related mortality during the swim-up life stage, and 4) mortality fr om fish predation shortly after swim-lip. Managers need to reconsider current strategies and time requirements necessary to achieve restorat ion goals and objectives for lake trout in Lake Ontario.