Maximum sustainable yield from interacting fish stocks in an uncertain world: two policy choices and underlying trade-offs

TL;DR

This study evaluates various fisheries management strategies using complex food web models to identify approaches that maximize sustainable yields while balancing ecological and policy trade-offs.

Contribution

It introduces a self-optimising control rule robust to ecosystem instability and compares multiple management plans, highlighting their effectiveness and trade-offs.

Findings

Stock-targeting plans outperform pressure-targeting plans in yield.

The new control rule achieves intermediate yields with robustness.

Multi-species interaction-aware plans are more effective and robust.

Abstract

The case of fisheries management illustrates how the inherent structural instability of ecosystems can have deep-running policy implications. We contrast ten types of management plans to achieve maximum sustainable yields (MSY) from multiple stocks and compare their effectiveness based on a management strategy evaluation (MSE) that uses complex food webs in its operating model. Plans that target specific stock sizes ($B_{\text{MSY}}$) consistently led to higher yields than plans targeting specific fishing pressures ($F_{\text{MSY}}$). A new self-optimising control rule, introduced here for its robustness to structural instability, led to intermediate yields. Most plans outperformed single-species management plans with pressure targets set without considering multispecies interactions. However, more refined plans to "maximise the yield from each stock separately", in the sense of a Nash equilibrium, produced total yields comparable to plans aiming to maximise total harvested biomass, and were more robust to structural instability. Our analyses highlight trade-offs between yields, amenability to negotiations, pressures on biodiversity, and continuity with current approaches in the European context. Based on these results, we recommend directions for developments of EU fisheries policy.