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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.

Workshop 2 on age reading of North Sea plaice (Pleuronectes platessa), (WKARP2) was the first age reading workshop focusing specifically on age reading of the North Sea plaice stock (ple.27.420) in the North Sea and Skagerrak. The objectives of the workshop were: to evaluate the level of agreement between age readers for the stock by reviewing results of the 2020 North Sea Skagerrak plaice exchange in consideration of previous calibration and validation work; to standardize laboratory procedures and age reading methods applied; to provide guidelines for reliable age interpretation; to provide age error data to the stock assessment working group; to create an agreed age reference collection of otoliths. Two age reading exercises, one exchange before the workshop (SmartDots ID 281), and one workshop exercise (ID 402) were completed using SmartDots1. Age readers’ annotations of growth structures and ageing results from both exercises were examined using standardized quality analyses based on an R script , presented in this report. Age reading error data has been provided to the ICES WGNSSK2 (Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak) which can be tested in the ple.27.420 stock assessment model. Disagreement between readers is mostly attributable to differences in the identification of the first winter ring as this can vary in width across samples collected from different areas. Results showed that estimated ages in older fish can be unreliable due to a narrowing of the annuli close to the otolith edge. Further work is required to provide guidelines for age readers about which structures should be identified as annuli. Different preparation methods are applied in national laboratories. The group concluded that reading whole and sectioned otoliths viewed under reflected light is optimal; no obvious benefit was identified from sectioning plaice otoliths from fish under the age of 6. Using images of otoliths, the reliability of the age reading results is depending on image quality. To help standardize image format, lighting and calibration a workshop is recommended to establish a set of guidelines for image quality used in age determination.

Parasites play a key role in the biodiversity and dynamics of an ecosystem, either by affecting host mortality and/or host reproduction. Spawning comes with a great cost in time and energy, and in times of poor conditions this time and energy is better directed into growth and survival to increase future success. The phenomenon of skipped spawning, where sexually mature fish skip a reproductive event, is a common occurence in the NEAC. Previous studies suggest that as much as 24-30% of females skip annual spawning, and instead remain at the feeding grounds. The causes for this is still unclear but it seems to occur in response to poor condition. As parasites, by definiton, have a negative effect on host fitness it is of finterest to see if parasites could affect the decision to skip spawning. In this study, we explore the effects of parasites on reproductive parameters in the Northeast Arctic cod (NEAC), the largest cod stock in the world. By comparing intensity of infestation in skippers and spawners we found that parasites do not seem to have an effect on the reproductive abilities of the NEAC. No significant differences in parasite intensity could be detected between skippers and spawners in any of the species included in our study. Nor were there any evidence to show that increase in parasite intensity were associated with decreased fecundity. Even an attempt to look at the effects of the whole parasite community by applying an intensity rank index did not find any correlation between infestation and reproductive parameters. However, caution must be made when making conclusions about parasites effect on host population dynamics. This demonstrates the importance of experimental studies of relationships between parasites and reproductive success. As well as look at parasite-induced host mortality in NEAC.