Genetic mixture analyses in support of restoration of a high value recreational fishery for rainbow trout (Oncorhynchus mykiss) from a large lake in interior British Columbia

摘要

Genetic mixture analysis is an important tool to apportion catch amongst potential component populations contributing to a fishery. We used variation at 10 microsatellite DNA loci to assess the level of genetic divergence between two ecotypes of rainbow trout (Oncorhynchus mykiss) that naturally co-occur in Kootenay Lake, southeastern British Columbia, and to exploit such divergence in a mixture analysis. One form, Gerrard rainbow trout, historically matured at sizes greater than 60cm and 5kg, spawns at a lake outlet after upstream migration in a large river tributary to Kootenay Lake, and is highly prized in the recreational fishery. The other form, non-Gerrard rainbow trout, is also native to the lake and matures at smaller sizes and spawns in numerous small streams tributary to Kootenay Lake. Recent declines in growth rate of Gerrard rainbow trout, however, has made them difficult to identify by size in fishery samples. Gerrard (N=130, 6 sites) and non-Gerrard trout N=312, 15 sites) were highly divergent from one another (F-ST=0.14, P<0.001) and constituted distinct genetic groups in model-based clustering analyses. Genetic mixture analyses of fishery samples indicated a high degree of accuracy in estimating mixture proportions; 100% Gerrard simulated fisheries were estimated to contain 99.9% Gerrards (95% confidence intervals of 99.8-100%) while 100% non-Gerrard rainbow trout simulated fisheries were estimated to contain 100.0% non-Gerrard trout (100-100%). Across eight fishery creel samples obtained between 2015 and 2017 (N=527 fish), mixture analysis estimated the fishery to contain an average of 73.4% (95% confidence interval=68.4-74.6%) Gerrard and 26.6% (23.4-31.6%) non-Gerrard trout. Realistic fishery simulations demonstrated strong agreement with empirical results; the average simulated values for Gerrards was 73.4% (65.9-80.0%) and for non-Gerrards was 26.8% (20.0-34.1%). Assignment tests resulted in an average 98.5% (+/- 0.066%) assignment confidence; 3