Abstract
Naturalization of a species requires self-sustaining populations without supplementation. Chinook Salmon are stocked into Lake Ontario to control non-native Alewife and provide a sportfishery worth $350 million to local economies. Hatchery stocking is often viewed by anglers and fisheries managers as the principal source of maintaining catch rates, thus, stocking decisions are controversial and set with limited information about contribution of wild salmon. Objectives of this dissertation were to use scale pattern analysis, mass marking and tagging to: 1) determine the relative contribution and distribution of wild and hatchery Chinook Salmon to Lake Ontario fisheries; 2) compare survival, imprinting and straying outcomes of hatchery stocking methods among tributaries and to the hatchery; 3) compare size at age and age at maturity of hatchery and wild salmon; 4) estimate straying rates of hatchery Chinook Salmon in Lake Ontario compared to native populations; and 5) consider the potential for local adaptation and naturalization of Chinook Salmon to Lake Ontario and implications to fisheries management. Wild Chinook Salmon have represented an important component of the fisheries for at least three decades averaging 46% of the lake harvest (range:23-61%) and varying significantly among tributaries (range: 9-59%). Hatchery salmon were significantly larger than wild salmon by 50 mm in July and were 20% more likely to mature at age 2. Recoveries of tagged salmon indicated a well-mixed population in the lake prior to September. Pen-acclimation provided 2.1 times higher relative survival than direct stocking, improved imprinting to tributaries, and significantly reduced straying to the rearing hatchery. Most salmon harvested in tributaries were stocked at those sites (mean=67%, SE=4%) or nearby, indicating good imprinting by both pen and direct-stocked salmon. Straying rates of hatchery Chinook Salmon were similar to those reported in native ranges of western North America, averaging 6.8% (range 0.1-23.9%) among Lake Ontario tributaries, and 11% to the rearing hatchery. Although local adaptation and naturalization may be occurring in some Lake Ontario tributaries, the potential is limited by intensive fisheries and stocking from central hatcheries. Hatchery and wild Chinook Salmon are important drivers of population dynamics and both require consideration when managing predator prey balance.