International Bottom Trawl Survey Working Group (IBTSWG)

The International Bottom Trawl Survey Working Group (IBTSWG) coordinates fishery-inde-pendent multispecies bottom-trawl surveys within the ICES area. These long-term monitoring surveys provide data for stock assessments and facilitate examination of changes in fish distri-bution and abundance. The group also promotes the standardization of fishing gears and meth-ods and survey coordination. This report summarizes the national contributions in 2020–2021 and plans for the 2021–2022 surveys coordinated by IBTSWG. In the North Sea, the surveys are performed in quarters (Q) Q1 and Q3 while in the Northeast Atlantic the surveys are conducted in Q1, Q3, and Q4 with a suite of 14 national surveys covering a large area of continental shelf that ranges from North of Scotland to the Gulf of Cádiz. Despite the COVID-measures and bad weather, most surveys were able to complete the majority of the planned hauls. The Portuguese survey (PT-GFS-Q4) was cancelled in 2020 due to issues associated with the new vessel and a COVID-outbreak. A COVID-related delay in submitting the cruise application form for the French CGFS20 survey resulted in no authorisation to trawl in UK waters and only 70% of the core stations were completed. Issues with the UK permits, were also experienced in the North Sea surveys, only being resolved at the last moment, expected to be a returning issue. Therefore, IBTSWG addressed the permit issue in further detail in order to better evaluate the impact and propose possible solutions.
All surveys, except for the Spanish GCGF-Q1 21 which is cancelled due to a vessel refit, are planned to take place according to the manuals in the next year.
The SCOROC Q3 20 survey recorded second highest recruitment of zero group haddock on the Rockall Bank since the start of the new survey series in 2011. The North Sea Q1 21 survey rec-orded good recruitment of haddock as well, and high recruitment of mackerel, while overall herring recruitment seemed low except for three exceptionally large catches in the Skager-rak/Kattegat bringing the index above average. Both North Sea surveys reported large amounts of target species outside their index areas, which may warrant a revision of the species-specific areas on which the standard abundance indices are calculated.
IBTSWG will continue a number of collaborative activities later this year. The Workshop on the Further Development of the New IBTS Gear (WKFDN) will focus on updating results of gear trails with the potential new gears. The Workshop on the production of swept area estimates for all hauls in DATRAS for biodiversity assessments (WKSAE) will continue work on the North-eastern Atlantic Flexfile available via DATRAS, for which country specific algorithms are used to fill data gaps relevant for the calculation of the swept area. This and the already available North Sea Flexfile can be used to produces swept area indices. IBTSWG also met with members of the assessment groups, Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK) and Working Group on Elasmobranch Fishes (WGEF), to improve communication on for example circumstances affecting the execution of the surveys but also changes in survey design potentially impacting the indices.

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ICES (2021). International Bottom Trawl Survey Working Group (IBTSWG). ICES Scientific Reports/Rapports scientifiques du CIEM. 3 (69). 201p..,

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