Ending overfishing and rebuilding fish stocks to levels that provide for optimum sustainable yield is a concern for fisheries management worldwide. In the US, fisheries managers are legally mandated to end overfishing and to implement rebuilding plans for fish stocks that fall below minimum stock size thresholds. These plans should lead to recovery to target stock sizes within ten years, except in situations where the life history of the stock or environmental conditions dictate otherwise.
Federally-managed groundfish species along the US West Coast have diverse life histories, where some are able to rebuild quickly from overfished status, while others, specifically rockfish, may require decades. A management strategy evaluation (MSE) was conducted to evaluate the performance of alternative strategies for rebuilding four alternative US West Coast life history types. The MSE identified the ability of these strategies to rebuild stocks and the trade-offs among alternative approaches.
Plans that set fishing mortality and rebuilding target years based on a higher initial rebuilding probability of ≥ 60% (i.e. the calculated probability of a stock returning to target sizes under the assumed population dynamics) generally achieved rebuilding by the target year with fewer changes to the harvest rate, particularly for stocks with longer plans. This can offer a measure of predictability for stakeholders.
Additionally, for the strategies that also allowed for a lower threshold probability (40%) during rebuilding, harvest rates were less responsive to noise (e.g. assessment error or transient trends in lower or higher recruitment). This approach was successful in meeting rebuilding targets while limiting the number of changes to harvest rates.
Maintaining a 50% probability of rebuilding was the poorest performing strategy, resulting in a high number of harvest rate changes, an increased frequency of failure to meet targets, and a higher variation in catch. The simplest strategy, which set a constant fishing mortality rate to rebuild the stocks, resulted in higher catches relative to other strategies while the stocks were rebuilding, but it also required longer rebuilding times.
These results highlight the trade-offs that must be considered when identifying rebuilding plans that best meet management goals.
The canary rockfish was one of several species of the rockfish genus that were looked at in the study. Photo: Gerick Bergsma 2010, Marine Photobank