Comparison of Adult Steelhead Migrations in the Mid-Columbia Hydrosystem and in Large Naturally Flowing British Columbia Rivers

Abstract The migration of 1,263 adult radio-tagged steelhead Oncorhynchus mykiss was assessed in the Nass, Skeena, Bella Coola, Fraser, and mid-Columbia rivers from 1993 to 2001. Of the summer-run steelhead tagged in the mid-Columbia River, 80–87% eventually continued their upstream migration after being tagged, and 87–90% of those were detected in spawning areas. Similar results were seen for summer-run steelhead tracked on the Nass and Skeena rivers. Mid-Columbia summer-run steelhead stocks that passed five dams en route to their spawning destinations (Methow and Okanogan rivers) traveled at a median rate of 20 km/d, which exceeded the median rates for summer-run steelhead tracked on the Nass (3.8 km/d) and Skeena rivers (12–16 km/d). The upstream migration rates were best explained by river gradient and distance of the study area from the ocean. When the effects of river gradient and reach location were taken into account, impoundment was still a significant factor increasing the upstream migration spe...