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Revisiting Fishery Sustainability Targets
Vincent Cattoni1, Leah F South2,3, David J Warne2,3
1The University of Queensland School of Mathematics and Physics, Saint Lucia, Australia.
Bulletin of Mathematical Biology
|September 16, 2024
Summary
Classic population models suggest harvesting at 40-50% of carrying capacity. However, the Hockey-Stick model, when applied to 284 fish species, often recommends higher population sizes for sustainable harvest.
Area of Science:
- Ecology
- Fisheries Science
- Population Dynamics
Background:
- Density-dependent population dynamic models are crucial for global harvest policies.
- Established models like Beverton-Holt and Ricker typically advise maintaining populations at 40-50% of carrying capacity for maximum sustainable harvest.
- These models form the basis for most fisheries' sustainability targets and biomass reference points.
Purpose of the Study:
- To investigate the recommendations of the Hockey-Stick model compared to classic models (Beverton-Holt, Ricker) for fisheries harvest policies.
- To analyze how model choice and parameter estimation influence optimal population size targets.
- To assess the implications of model uncertainty for fisheries management.
Main Methods:
- Fitted the Hockey-Stick, Ricker, and Beverton-Holt models to population time series data from 284 species in the RAM Stock Assessment database.
- Compared the recommended optimal population sizes (as a proportion of carrying capacity) across the three models.
- Conducted a computational experiment simulating data from each model to evaluate model-fitting performance and uncertainty.
Main Results:
- The Hockey-Stick model generally recommended higher population sizes than the Beverton-Holt and Ricker models (in 69-81% of datasets).
- In 77% of datasets, the Hockey-Stick model suggested targets exceeding 60% of carrying capacity.
- Model fitting showed considerable uncertainty, with the best-fitting model rarely having strong support (>95% probability).
- The Beverton-Holt model often fit best even when it was not the generating model, indicating data limitations.
Conclusions:
- Fisheries data may be insufficient to definitively distinguish between density-dependent growth models.
- The widespread reliance on classic models may lead to suboptimal harvest strategies, particularly for slow-growing species.
- Sustainability targets and biomass reference points may require re-evaluation based on a broader range of population dynamic models.
