Habitat Capacity for Chinook Salmon and Steelhead Spawning and Rearing in the Similkameen River Basin

M. H. Bond
2023
We conducted a geomorphic analysis of potential salmon habitat in the basin, assuming unimpaired passage of Chinook salmon (Oncorhynchus tshawytscha), and steelhead (Oncorhynchus mykiss) into the mainstem Similkameen River past Coyote Falls and the Enloe Dam site. The Similkameen River has been inaccessible to anadromous fish since 1922, when Enloe Dam was constructed at river kilometer 14. We determined the anadromous extent of the basin with a combination of ground survey barrier
more » ... n from the Upper and Lower Similkameen Tribes, and maximum accessible stream gradients derived from topographic information (Canada 20 m DEM and LiDAR 1 m), resulting in 2446 km of accessible habitat out of all 5504 km of streams in our Similkameen River Basin dataset. We used catchment area and average annual precipitation of each reach to estimate stream size and a total average wetted habitat area of 2193 hectares. We estimated spawning gravel areas for each species based on stream slope and pool spacing. The spawning habitat divided by average redd area indicated a redd capacity of 80,705 and 210,729 for Chinook salmon and steelhead, respectively. In addition, we estimated juvenile rearing habitats in large rivers (large stream banks, bars, mid-channel, and side channel), and smaller streams (pools and riffles). For each estimated habitat type area, we applied literature-derived parr densities to estimate a total parr rearing habitat capacity of 6,645,841 and 10,252,583 for Chinook salmon and steelhead, respectively. Applying an average parr to smolt survival for each species, we estimate parr at capacity would result in ca. 1.5 million Chinook smolts and 2.9 million steelhead smolts, similar to previous estimates for the Similkameen River. At recent smolt to adult survival rates for the Upper Columbia, smolt abundances of these magnitudes would likely result in ca. 7,800-47,000 Chinook salmon spawners, and 29,500-118,300 steelhead spawners returning to the Similkameen River.
doi:10.25923/xf8y-x065 fatcat:nxfsthcggvcadgcj4hjgvzresy