Refining indices of risk from salmonid hatcheries

ABSTRACT Objectives The risk to wild populations from domestication selection in hatcheries is commonly indexed with estimates of the proportion of hatchery-origin spawners (pHOS) on natural spawning grounds. Widely used calculations of pHOS are not commensurate with the genetic theory that motivates the use of pHOS as an index of risk from domestication selection. Methods I derive an alternative metric of pHOS that is commensurate with the spatiotemporal variability of natural- and hatchery-origin fish and the genetic theory used to index risk. I describe nuances that are associated with indices of hatchery risk, including how to calculate variances. Results The widely used calculation of pHOS will overestimate the risk when the densities of breeding natural- and hatchery-origin fish differ in space or time. The analytics provided here will improve the empirical estimation of an index of risk from hatchery-origin fish and the associated uncertainty. Conclusions Clarifying the calculations and interpretations of indices of risk to natural-origin fish can help managers balance multiple management goals associated with hatchery production.