Cumulative effects of multiple sources of bias in estimating spawner–recruit parameters with application to harvested stocks of Chinook salmon (Oncorhynchus tshawytscha)

Previous studies of bias in estimating spawner–recruit relationships have usually focused on a single source of bias, and have typically found bias that tends to overestimate productivity and underestimate optimal population size. However, many of these studies have used simulated data contrived to maximize the bias. This study examined the cumulative effects of multiple sources of bias using simulations with life history parameters based on Chinook salmon (Oncorhynchus tshawytscha) stocks used as escapement indicator stocks for management of ocean salmon fisheries. Sources of bias incorporated in the simulations include time series bias, observational errors, and errors in estimating age composition. Cumulative biases in parameter estimates were found to be relatively small in most cases, and the resulting management reference points tended to err in the direction of conservation rather than in the direction of overexploitation. However, the same methods applied to depleted stocks would result in substantial bias that would tend to contribute to overexploitation.