Three fishes
Status of fish and shellfish stocks provides essential knowledge for authorities working to manage them sustainably. Photo: Jörgen Wiklund

Stock assessments

Page reviewed:  11/06/2025

The Department of Aquatic Resources (SLU Aqua) conducts annual analyses and biological assessments for more than 100 species and stocks of fish and shellfish. The results serve as scientific input to both national and international fisheries management.

These biological assessments provide a knowledge base for various authorities managing fishery resources. The aim of management is to keep stocks within biologically safe limits and thereby achieve key environmental objectives.

Stock assessments and advice within ICES

Many fish species migrate across wide areas and are not restricted by national fishing zone boundaries. These species require international cooperation, which takes place within the International Council for the Exploration of the Sea (ICES), involving participants from all coastal states around the Baltic Sea, the North Sea and the North-East Atlantic. Around 50 researchers from SLU Aqua participate in ICES work, distributed across various working groups.

Based on annual stock assessments, ICES provides advice on recommended catch levels according to a management objective of maximum sustainable yield. For a number of internationally managed species, the EU’s fisheries ministers then decide on the annual catch quota for each stock and how the quota is to be allocated between countries.

Read more about the ICES process in the text From data collection to quota decision. All ICES advice is published openly and can be searched via ICES's latest advice webpage.

Stock assessments of nationally managed species

For species managed at national level—such as perch, pike, pike-perch, and whitefish along Sweden’s coasts, as well as many species in the five largest Swedish lakes (Vänern, Vättern, Mälaren, Hjälmaren and Storsjön)—SLU Aqua conducts the stock assessments and provides biological evaluations to the responsible management authorities.

These analyses use three categories of indicators: fishing mortality, biomass/abundance, and size/age structure. For each stock, these indicators are combined to assess the biological status of the stock according to the following classification:

  • The stock is very likely within biologically safe limits
  • The stock is likely within biologically safe limits
  • The stock is likely not within biologically safe limits
  • The stock is very likely not within biologically safe limits
  • The stock cannot be assessed

Analyses of both internationally and nationally managed species are, as of 2023, published annually on SLU’s web portal Fiskbarometern.se 

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