Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Yolanda Morbey


Chinook salmon (Oncorhynchus tshawytscha) were introduced into the Great Lakes to restore top-down control of the food web and create new recreational fisheries. Soon after introduction, naturalized spawning populations became established, and with continued stocking of hatchery fish, created a mixed source fishery. My research provides new ecological information about the contributions of naturalized fish to the mixed source Chinook salmon fishery in Lake Huron. I examined spawning and foraging habitat use by naturalized and hatchery Chinook salmon using multiple methods to identify sources of individual fish (external tags, hatchery fin clips, and otolith microchemistry). In the Sydenham River, Ontario, one of the earliest sites of documented natural reproduction, hatchery fish composed >50% of spawning fish in 2010 and 2011. Hatchery and naturalized fish arrived and spawned throughout the river in similar patterns despite evidence of hatchery females directly homing to their stocking site. Increased pre-spawning movement by smaller and later arriving females was evidence that similar habitat use may have resulted from despotic behaviour in the limited amount of accessible habitat (≈ 6 km). Thus, hatchery and naturalized fish showed some differences in behaviour but showed no evidence of reproductive isolation in space or time. I used otolith microchemistry and hatchery fin clips to assigning natal source to Chinook salmon captured in the 2008 and 2010 fisheries to examine in-lake stock composition. In the lake, naturalized fish comprised 66% of fish sampled and the majority of these naturalized fish originated from rivers flowing into Georgian Bay (55%) and northern Lake Huron (35%) while most hatchery fish originated from Michigan hatcheries (67%). Furthermore, there was evidence of incomplete mixing and extensive interbasin movement. Georgian Bay rivers contributed fish lake wide, Michigan hatcheries were dominant contributions in Northern Main Basin, and contributions of fish from central and southern Lake Huron rivers were limited. My thesis provides the first individual based examination of habitat use by naturalized and hatchery Chinook salmon in the Great Lakes, providing basic but crucial information needed by researchers and managers for understanding population dynamics and for sustainably managing the lake ecosystem.