Parentage-based tagging and genetic stock identification applied to assessment of mixed-stock fisheries and hatchery broodstocks for Chinook salmon in British Columbia, Canada

Genetic stock identification (GSI) and parentage-based tagging (PBT) are being increasingly applied to salmon fisheries and hatchery broodstock management and assessment in Canada. GSI and PBT with single nucleotide polymorphisms (SNPs) were applied in assessment of 2020 Chinook salmon fisheries and hatchery broodstocks in British Columbia (BC), Canada, with 9234 individuals successfully genotyped in fishery samples and 2250 PBT identifications made (24.4% individual identification rate). As PBT identifications provided age of the individual and sex was determined from a SNP in the SNP panel, it was possible to evaluate sex ratios by age observed in the fishery sampling. Fishery catch sex ratios at age two and three years were male-biased, whereas those at age four and five years were female-biased. The combined age and sex information derived from genetics-based fishery sampling illustrates the ancillary information that becomes available relative to coded-wire tag (CWT) sampling if biological sampling of the catch is not conducted. There were 20,342 individuals genotyped in 65 hatchery broodstocks from which 6080 PBT identifications were made. Population-specific contributions to mixed-stock fisheries and exploitation rates were estimated with CWTs and GSI-PBT technologies for 13 populations, and close agreement of estimated population-specific exploitation rates between CWT and genetic methods for the 13 populations was observed (r2(11)= 0.951, P < 0.001). We conclude that a genetic approach can improve upon the results available from the current CWT program for assessment and management of Chinook salmon fisheries and hatchery broodstocks in BC, as well as provide ancillary information to improve wild Chinook salmon assessment and conservation by providing fishery impacts by conservation unit for any fishery in Canada.