Dynamic harvest control rules for fish stocks with time-varying productivity
Using three fish stocks with time varying stock recruitment relationships, this study compares harvest control rules and reference point strategies under changing productivity. Results show that adaptive harvest policies can better maintain biomass during low productivity periods and increase yields when productivity improves, supporting more responsive fisheries management.
Subject Tags
- Fisheries
- Ecosystem management
Abstract
Biological reference points are benchmarks against which stock status can be assessed and are central to fisheries management advice. Calculation of non-proxy reference points depends on the demographic parameters of the stock, particularly stock-recruitment parameters. There is growing evidence of non-stationary, pre-recruit mortality parameters that would imply time-varying reference points. It may be possible, however, to develop robust (time-invariant) harvest control rules (HCRs) that can partially mitigate for dynamic mortality parameters via lagged biomass dependency. It is unclear under what conditions either approach would be preferable. To address this question, we use time-varying stock-recruitment relationships for three contrasting stocks and counterfactually manage plausible histories under: (1) constant proxy fishing mortality F target; (2) time-varying target F; (3) constant biomass-linked HCR; and (4) a time-varying biomass-linked HCR. In contrast to a previous study that found conservation gains with constant, status-quo management targets, we find that time-varying HCR policies were able to maintain higher levels of biomass during low-productivity periods and achieve higher yields during periods of high productivity. These benefits result from not fixing reference points to proxies that become outmoded when productivity varies. We find that a time-varying harvest policy may be advantageous when the productivity signal is strong and persistent over decadal time scales. The performance of a time-varying HCR will also be improved when there is a short time lag between assessing productivity and adjusting the fishing mortality rate. By contrast, a time-invariant HCR will be favored for stocks with weaker productivity signals relative to the short-term recruitment variability or longer assessment lags and possibly older recruitment ages. While some generalization is possible, we recommend that time-varying harvest policies be evaluated on a stock-by-stock basis using this approach.
Citation
Jeremy S Collie, Richard J Bell, Paul D Spencer, Rachel C Marshall, Cóilín Minto, Dynamic harvest control rules for fish stocks with time-varying productivity, ICES Journal of Marine Science, Volume 83, Issue 8, August 2026, fsag154, https://doi.org/10.1093/icesjms/fsag154
TNC Authors
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Richard J Bell
Sr. Fisheries Scientist. Provide Food and Water
The Nature Conservancy
Email: rich.bell@tnc.org