Sensitivity of Fishery Management Performance to Alternative Frequencies of Stock Assessments

We evaluated the influence of assessment frequency (annually or less often) using simulations based on Lake Whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes of North America, which are assessed using age-structured models and managed with a constant mortality target. We also explored the influence of different approaches to setting target harvests in years between full assessments, productivity, recruitment variation, and target mortality rates. Assessment frequency had a modest influence, with a tendency toward lower yield, higher spawning biomass (SSB), and higher interannual variability in yield with less frequent assessments. Populations with low productivity and subject to a high mortality target were most sensitive to the decrease of assessment frequency. High recruitment variation led to more variable management performance metrics, but did not change median values. We saw more substantial effects due to how target harvest was set between full assessments. Retaining the target harvest calculated for the year of the last assessment, between assessment years, led to the highest and most stable yields. Setting target harvest between assessments based on population projections that accounted for yield led to the greatest SSB, whereas projections based on target fishing mortality had the lowest SSB and no benefit in yield.