Use of PIT and Acoustic Tags to Estimate Survival of Adult Sockeye Salmon in the Okanagan Basin

The Canadian portion of the Okanagan River supports the majority of the total sockeye salmon (Oncorhynchus nerka) production in the Columbia Basin. However, the Okanagan River is listed as one of the most endangered rivers in British Columbia, mainly due to impacts from agriculture, irrigation, and urban development.  To contribute to the restoration and understanding of Okanagan River sockeye we acoustically tagged and tracked adult sockeye migrating into the Okanagan River to determine migration timing, fate, and critical life history information. Sixty four adult sockeye were trapped and acoustically tagged, while a total of 400 adults were PIT tagged at Wells Dam, south of Pateros, Washington. Tags surgically implanted in four groups each week through July 2010. Subsequent monitoring was conducted via the installation of 25 Vemco VR2W’s placed in strategic locations along both the Washington and British Columbian portions of the Okanagan River and within Osoyoos Lake, the major sockeye rearing lake within the basin. Additionally, for 2010 PIT arrays were installed both at Zosel Dam (ZSL) – the outlet to Osoyoos Lake, and within the Okanagan River (OKC) at VDS 3, Rd 18, Oliver BC. We found 76.5% of the acoustic tags survived the migration into Osoyoos Lake while 59% of all acoustic tagged fish survived to reach the Okanagan River spawning grounds, similarly PIT data from OKC demonstrated 70-75% survival from Wells Dam to OKC. Additionally, Osoyoos Lake is a critical rearing reservoir that consists of three basins that experiences O₂/temp squeezes during hot summer months. Acoustic data suggests less than 12 hour swim timing through the South basin into both the Central and North Basins of Osoyoos Lake. Depth and temperature data indicate refuge of predominantly 8-10^⁰C at ~30m depth within the North Basin. Broadly, the timing of migration during the 2010 season was not hindered by a thermal barrier.