Baltic International Fish Survey Working Group (WGBIFS)

The Baltic International Fish Survey Working Group (WGBIFS) plans, coordinates, and implements demersal trawl surveys and hydroacoustic surveys in the Baltic Sea including the Baltic International Acoustic Survey (BIAS), the Baltic Acoustic Spring Survey (BASS), and the Baltic International Trawl Surveys (BITS) in the 1st and 4th quarter on an annual basis. The group compiles results from these surveys and provides the herring, sprat, cod and flatfish abundance indices for the Baltic Fisheries Assessment Working Group (WGBFAS) to use as tuning fleets.

In 2024, WGBIFS compiled survey results from 2023 and the first quarter of 2024, planned and coordinated all surveys for the second half of 2024 and the first quarter of 2025 relevant to the assessments of the Baltic fish stocks. Data collected during the recent BITS surveys were added to the ICES Database of Trawl Surveys (DATRAS). Also, the Tow-Database was corrected and updated accordingly. The Access-databases for aggregated acoustic data and the ICES database of acoustic-trawl surveys for disaggregated data were updated. All countries registered collected litter materials to DATRAS.

The area coverage and the number of control hauls in the BASS, BIAS and GRAHS in 2023 were considered to be appropriate to the calculation of tuning indices and the data can be used for the assessment of Baltic herring and sprat stocks. The number of valid hauls accomplished during the 4th quarter 2023 and 1st quarter 2024 BITS were considered by the group as appropriate to tuning series and the data can be used for the assessment of Baltic and Kattegat cod and flatfish stocks. BIAS survey standard deviation for Central Baltic herring acoustic index was calculated.

WGBIFS is planning to continue with comparison exercises between the StoX method and traditional Gulf of Riga Herring Survey calculation method in the coming years before the final transition to a transparent reproducible pathway into the ICES Transparent Assessment Framework (TAF) can be done. Work towards transitioning to TAF will continue during this 3-year period until all methodological and database differences are resolved.

Issues related to the data quality of demersal trawl surveys were discussed. Focus was directed towards visualization and comparison of the main results. It was also suggested that the group should more focus on the comparison of haul parameters between the participating countries. The group plans to revisit this issue during the next meeting.

Information on how different countries are handling the closed areas (offshore wind power plants and marine protected areas), that are restricted for scientific vessels to conduct the surveys, was gathered. A study, that explored how the spatio-temporal coverage of the acoustic surveys could be improved through the modelling approaches, was presented.

Survey manuals were reviewed and several suggestions about the possible changes and corrections were listed. Inquiries from other ICES expert groups were discussed and addressed.