[Publication] Fisheries management in the Baltic Sea. The shift to ecosystem reference points (ERPs)

Background

The Baltic Sea is facing a critical fisheries management failure. Four of the seven key commercial stocks − including Western and Eastern Baltic cod as well as the two main herring stocks − are now critically depleted, with spawning stock biomass (SSB) far below biological limits. A common issue is the structural overestimation of stock size and productivity of most Baltic fish stocks, which led to years of undetected overfishing. These failures reflect both structural weaknesses of the MAP and external pressures, such as climate change, eutrophication and compounded assessment errors. Traditional single-species reference points (e.g. F_MSY, B_lim) have proven insufficient to ensure resilience under deteriorating ecosystem conditions.

Aim

The briefing examines how ecosystem reference points (ERPs) and complementary indicators of stock structure (size and age) can be integrated into EU fisheries management. It evaluates scientific approaches already developed in other regions, their relationship to existing biomass targets, and their operational feasibility in the Baltic Sea. It also assesses how such tools could be anchored in EU law.

Results

The concept of ERPs has emerged as a central tool for improving fisheries management. ERPs extend the scope of management to the ecosystem as a whole, in contrast to conventional single-species targets, such as the fishing mortality at maximum sustainable yield (F_MSY) or the biomass below which the reproductive capacity of the fish stock is impaired (B_lim). They define a “safe operating space” that integrates productivity, trophic relationships and environmental capacity, providing guardrails that can override overly optimistic single-stock advice. For the Baltic Sea − an ecosystem undergoing irreversible physical and biological change − the goal cannot be to restore historical states, but rather to establish contemporary reference conditions that are stable, productive and resilient to current pressures.

Operationalising ERPs is not a theoretical exercise. Case studies from around the world provide concrete examples. The Atlantic menhaden fishery in the United States demonstrated how models of intermediate complexity can balance predator-prey trade-offs, leading to fishing mortality targets reduced by nearly 40% compared to single-species advice. In Europe, ICES has pioneered the F_ECO approach, which scales single-species fishing mortality targets within the F_MSY range according to environmental indicators such as temperature or zooplankton biomass. Other innovations include ecosystem productivity caps, as successfully applied in the Bering Sea, and trophic-based benchmarks that detect ecosystem degradation once cumulative biomass falls below one-third of its reference level.

Beyond ecosystem-scale benchmarks, the Marine Strategy Framework Directive (MSFD) offers a ready-made legal basis for operationalising structural indicators. Descriptor 3.3 (D3.3), which requires monitoring of age and size distributions, can be implemented immediately using available proxies such as the large fish indicator (LFI) and length-based spawning potential ratio (SPR). These metrics provide empirical checks against systematically optimistic stock assessments and can be embedded in harvest control rules (HCR) to enforce precautionary overrides when stock structure deteriorates.

For these approaches to become binding, legal pathways within the Common Fisheries Policy (CFP) must be activated. The Baltic MAP should be amended to include ERPs as binding, precautionary targets comparable to B_lim or MSY B_trigger. Regionalisation under Article 18 further enables Member States, through BALTFISH, to advance ecosystem measures within a nine-month cycle. Together, these pathways make the formal integration of ERPs both feasible and urgent.