Background/Aims
Estimates of stock status and catch limits can change dramatically with new data or modeling approaches. Such fluctuations create undesirable socioeconomic impacts. This study evaluated strategies minimizing catch variation while mitigating ecological risks when assessments indicate status changes. We investigated: 1) which assessment parameters cause ±25% bias in overfishing limits, 2) how harvest control rules (HCRs) perform under consistent mis-specification, 3) HCR performance when mis-specification occurs only initially, and 4) impacts of removing the overfishing limit (OFL) constraint requiring Acceptable Biological Catches (ABC) to be less than the OFL.
Methods
We compared four HCRs using management strategy evaluation across two fish life histories. Parameters in the assessment model (natural mortality, stock-recruitment steepness, catch history, and selectivity) were deliberately mis-specified to create ±25% bias in overfishing limits. We examined HCR performance under three reference scenarios: a) correctly specified assessment, b) consistently underestimated parameters (-25% OFL bias), and c) consistently overestimated parameters (+25% OFL bias). Additionally, we evaluated scenarios where mis-specification occurred only during the first assessment and was subsequently corrected. Performance metrics focused on minimizing catch variation and biological risk.
Results
HCR performance varied with life history and initial depletion. All HCRs maintained stable catches at for stocks with the least initial depletion, 0.48B₀. The status quo probability-based HCR stabilized catches for the 0.28B₀ and 0.34B₀ initial depletions after several years. The phase-in HCR performed similarly by preserving total catch while "phasing-in" catches over time. Using a 15% constraint, the ABC constraint HCR was the most conservative by gradually increased catches, while the F constraint HCR produced more stable changes in catch limits relative to the status quo HCR.
Conclusions
Our findings show these HCRs can effectively minimize catch variability and biological risk. The F constraint HCR offers greatest stability, providing potential socio-economic benefits, but increases risk for depleted stocks. Management frameworks with flexible HCRs can better balance competing objectives of stability and conservation, particularly under assessment uncertainty. Managers should consider life history characteristics and stock status when selecting appropriate HCRs.