Working Group on Baltic International Fish Survey (WGBIFS; outputs from 2020 meeting)

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 2020, WGBIFS completed the following tasks: (1) compiled survey results from 2019 and the first half of 2020, (2) planned and coordinated all Baltic fish stocks assessment relevant surveys for the second half of 2020 and the first half of 2021, (3) updated the common survey manuals according to decisions made during the annual WGBIFS meeting. Data from the recent BITS was added to the ICES Database of Trawl Surveys (DATRAS). The Tow-Database, which allows planning the spatial distribution of hauls in the areas where the seabed is suitable for safety trawling, was corrected and updated. The Access-databases for aggregated acoustic data and the ICES database of acoustic-trawl surveys for disaggregated data were also updated. All countries also registered collected litter materials to DATRAS.

The area coverage and the number of control hauls in the BASS and in the BIAS in 2019 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 2019 and 1st quarter 2020 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. Survey sampling variance calculations were also conducted for the BIAS and BASS surveys from 2012 to 2019. 

A comparison exercise between the StoX and traditional BIAS calculation methods was performed for the SD 30 herring. It was found that the StoX project, developed for the WGBIFS, has small methodological differences compared to the standard calculation method used by the group, as specified in the Manual for the International Baltic Acoustic Surveys, (IBAS) and is thereby causing a small difference in the total number of herring. Nevertheless, WGBIFS decided to recommend for the assessment purpose that the herring abundance time-series is calculated with StoX. 

WGBIFS is planning to perform in the coming years analogical comparison exercises between the StoX and IBAS calculation methods also for all other acoustic index series before the final transition to StoX and to a transparent reproducible pathway into the ICES Transparent Assessment Framework (TAF) can be done.