This report investigates the utility of using a numerical simulation model to identify the frequency, timing and magnitude of fishery openings that can protect 80% of the steelhead run from terminal fishing impacts, with 90% certainty, while ensuring that minimum spawning requirements are met. Historical records from the Tyee test fishery were used to examine run timing parameters preliminarily to constructing the simulation model; this exercise identified serious difficulties with the simulation approach due to high variability in the timing and peak period of the run, trends towards conditions that differ from the past, and data shortcomings. The report recommends that a more practical way to achieve 80% protection with 90% certainty would be to apply a rule-of-thumb approach (for example, to allow one day of fishery opening every few days once the run is well underway, provided that cumulative escapement suggests that minimum spawning requirements are likely to be met).