Conservation Targets and Constrained Optimization (Exposing Trade-offs in Mixed Stock Salmon Fisheries)

New policies, based upon the precautionary approach call for finer scale management of salmon fisheries in Canada. A critical and laudable element in the planning of these policies is the analysis of available escapement and harvest trend data so as to provide abundance reference points for as many stocks (or “Conservation unit” aggregates) as possible, and to assess stock status and risk of stock loss relative to those reference points. The implementation of these policies is carried out using Harvest Control Rules (HCR) and conservation benchmarks. In many cases these policies are being applied without an exploration of the costs and trade-offs associated with the chosen methods of implementation or the chosen benchmarks. Using simulation models and the Skeena River Salmon fisheries as a test case it is possible to use constrained optimization to investigate the effects of different harvest control rule application at different scales and with different conservation benchmarks on the harvests of different user groups. Constrained optimization and simulation can demonstrate the trade-offs between harvest taken by different user groups and the effects of different conservation benchmarks on those harvests.