International Bottom Trawl Survey Working Group (IBTSWG)
The International Bottom Trawl Survey Working Group (IBTSWG) coordinates fishery-independent bottom trawl surveys in the ICES area in the Northeast Atlantic and the North Sea. These long-term monitoring surveys provide data for stock assessments and facilitate examination of changes in fish distribution and relative abundance. The group also promotes the standardization of fishing gears and methods as well as survey coordination. This report summarizes the national contributions in 2021–2022 and plans for the 2022–2023 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 extends from the north of Scotland to the Gulf of Cádiz.
North Sea surveys in 2022-Q1 were affected severely by mechanical and COVID-related issues, as well as the number of storms experienced during the survey period. Some of the ICES rectangles in the survey area could not be sampled and a larger number of the rectangles were only sampled with a single tow.
North Sea surveys in 2021-Q3 were broadly complete, with the wider area surveyed and comparable number of hauls. However, some rectangles close to shore or with obstructions may not have had full coverage.
Most of the surveys in the Northeast Atlantic were completed successfully. However, the two Spanish groundfish surveys in the Gulf of Cádiz could not be undertaken in 2021. Vessel-related problems also affected the Spanish survey of the Cantabrian Sea, although this survey was completed using two vessels over a more protracted survey window. The IBTSWG welcomed the return of the Portuguese groundfish survey (Q4) after a two-year absence, with the survey being undertaken by the new research vessel, the “Mario Ruivo”.
IBTSWG discussed the roadmap for the new survey trawl, following on from the Workshop on the Further Development of the New IBTS Gear (WKFDN). IBTSWG agreed the main aspects of the new trawl, and will meet intersessionally to discuss and agree the final net plans. Trials are planned to start in late 2022 with the subsequent introduction of the trawl in the North Sea over the next few years.
IBTSWG met with members of various assessment groups, including the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK) and the Working Group for the Bay of Biscay and the Iberian Waters Ecoregion (WGBIE) to discuss how closer cooperation could enhance the use of data outcomes. IBTSWG members subsequently gave presentations to some of the assessment working groups using the data collected under the auspices of IBTSWG and intends to incorporate feedback into the its work.
The trawl surveys coordinated by IBTSWG also provide an important platform for the collection of additional data, including the sampling of sprat larvae, fish stomachs and fish parasites.
Published under the auspices of the following ICES Steering Group or Committee