Habitat Use and Arrival Timing of Hatchery and Naturalized Chinook Salmon Spawning in a Great Lakes Tributary

Abstract

AbstractLarge‐scale stocking programs have been used to introduce and maintain Chinook Salmon Oncorhynchus tshawytscha fisheries in the Laurentian Great Lakes since the late 1960s, with discoveries of naturalized populations in tributaries soon after the initial introduction. Characterizing ecological differences between hatchery and naturalized Chinook Salmon is becoming increasingly important for sustainable management of this species. We hypothesized that nonheritable traits (i.e., homing) and artificial selection might result in different habitat use and arrival timing between rearing origins occupying the same river, with the potential for reproductive isolation and divergence of naturalized and hatchery strains. In 2010 and 2011, using visual observations and PIT tags, we tracked individual hatchery and naturalized Chinook Salmon that spawned in the Sydenham River (Owen Sound, Ontario), one of the first tributaries in Lake Huron to be colonized by hatchery strays and establish a naturalized population. We estimated that 52–58% of the 3,200–3,300 fish returning to spawn in 3.5 km of accessible spawning habitat were hatchery fish. In females, the extent of prespawning movement increased with arrival date, decreased with fish length, and was lower for hatchery fish. Hatchery females also displayed a higher probability of direct homing to the stocking site than naturalized females. Prespawning movements by males were extensive but did not depend on rearing origin, arrival timing, or body size. We found no evidence of reproductive isolation, however. Spatial distributions of spawning locations were independent of rearing origin for both sexes, and arrival timing in the river was similar between rearing origins for both sexes. The lack of reproductive isolation is likely attributable to the small area of suitable habitat in this river. Our study represents the first comprehensive comparison of spawning habitat use and timing by hatchery and naturalized Chinook Salmon in the Great Lakes.Received October 26, 2016; accepted February 22, 2017 Published online April 24, 2017