Dynamics of Reproduction by Hatchery-Origin Lake Trout (Salvelinus namaycush) at Stony Island Reef, Lake Ontario

Abstract

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 and fry emergence were conducted on a spawning reef in the eastern basin of Lake Ontario to determine variables associated with poor reproduction 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 collect eggs and fry. Bags were retrieved on three dates over the six month period between the end of spawning and fry emergence. Mean egg abundance 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 Seneca strain spawners, rather than an increase in the total number of adults 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 fertilized eggs was probably due to physical shock caused by water currents during storms. Mortality later in development was caused by predation and 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 fertilization and egg-to-fry survival rate estimated in this study. Other parameters were estimated from stocking rates and previous studies. Model output indicated that the current lake trout population has the potential to produce over 1.2 million age-1 fish annually. No evidence exists for this level of recruitment in Lake Ontario. Natural recruitment may be limited by a low proportion of eggs incubating in suitable substrate and/or low survival of fry to age-1. These problems could be due to a combination of 1) a limited amount of spawning habitat, 2) ineptitude of some strains to locate or recognize spawning habitat, 3) disease-related mortality during the swim-up life stage, and 4) mortality from fish predation shortly after swim-up. Managers need to reconsider current strategies and time requirements necessary to achieve restoration goals and objectives for lake trout in Lake Ontario.