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The International Bottom Trawl Survey Working Group (IBTSWG) coordinate fishery-independent bottom trawl surveys in the ICES Area (Northeast Atlantic and North Sea) providing an important platform for the collection of additional data such as sampling larval sprat, stomach contents and fish parasites. These long-term monitoring surveys provide data for stock assessments and facilitate analyses of the distributions and relative abundance of fish. IBTSWG promotes the standardization of fishing gears and methods. This report summarizes national contributions in 2022–2023 and plans for the 2023–2024 surveys. In the North Sea, the surveys are performed in Quarter 1 and Q3. The Northeast Atlantic surveys are conducted mostly in Q1, Q3, and Q4 with a suite of 14 national surveys covering large areas of continental shelf extending from northern Scotland to the Gulf of Cádiz. The 2023-Q1 North Sea IBTS was impacted slightly by mechanical issues on one vessel, resulting in some of the Rectangles in the central North Sea being sampled with a single haul instead of the planned two. The 2022-Q3 North Sea IBTS was broadly complete, with the overall number of hauls comparable to previous years, though some Rectangles close to shore or with obstructions may not have had full coverage. The Northeast Atlantic surveys were mostly completed successfully, with the exception of the Scottish west coast groundfish survey in Q1 (cancelled due to vessel breakdown). There was incomplete survey coverage for some of the surveys, including the EVHOE survey (severe weather) and Portuguese groundfish survey (severe weather and mechanical problems). The Spanish surveys in the Gulf of Cádiz (cancelled in 2021) were undertaken in 2022. Recent updates to DATRAS, where the trawl survey data are stored, were summarised and data quality, including catch weights and species identification, was reviewed. IBTSWG met with members of various data users, including r

The Workshop on Unavoidable Survey Effort Reduction 2 (WKUSER2) focused on best-available approaches that can minimize information loss and ensure continuity in survey time series when unavoidable changes to survey effort occur. WKUSER2 recognised that reductions, reallocations, or increases in survey effort present similar set of problems, and therefore concentrated on all aspects of survey effort changes. The workshop reviewed available research, current practices, and recommended future directions on four key topics: (i) key elements of flexibility of a survey, (ii) why and how to combine data from different sources (e.g. surveys, fishery sampling) and deal with survey gaps, (iii) how to configure estimation and simulation models, and (iv) review existing tools and technology to evaluate consequences of survey effort changes. Road maps were developed for the key topic areas i, ii, iii, and iv, whenever possible, to assist scientists and survey managers in making decisions on how to evaluate and mitigate the impact of survey effort changes on data and advice quality. Many tools are available or are being developed for that purpose, but the group recognized two important needs during the workshop: i) defining clear objectives and priorities of a survey, which are essential to properly evaluate con- sequences of survey changes; and ii) making all tools accessible, reproducible, and transparent to benefit the whole community. This requires organisational and cultural shift to create support systems that ensure the development and sustainability of such tools in the future.

The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the national contributions on the results of the surveys conducted in 2022 together with time series covering all survey years, problems encountered, data quality checks and technological improvements as well as the planning for survey activities for 2023. In total, 21 surveys covering 26 functional units (FU’s) in the ICES area and 1 geographical subarea (GSA) in the Adriatic Sea were discussed and further improvements in respect to survey design and data analysis standardization and the use of most recent technology were reviewed. The first exploratory UWTV survey on the FU 25 Nephrops grounds was also presented to the group. The results of the evaluation of reference sets for FU3&4 Skagerrak/Kattegat were accepted following the process set down by the 2018 workshop (WKNEPS). An alternative method estimate Nephrops abundance was shown to the group using the recently published R package sdmTMB. The group agreed to hold a workshop in 2025 to address burrow size estimations to update correction factors and terms of reference for this to be agreed at next meeting. Automatic burrow detection based on deep learning methods continues to show promising results where datasets from multiple institutes were used. Plans are being progressed for an international Nephrops UWTV database to be established at the ICES data centre with a sub-group

The Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS) is responsible for the planning, data collection, and data analysis of the ICES triennial mackerel and horse mackerel egg surveys. This report focuses on the execution of the mackerel and horse mackerel egg survey (MEGS) in 2022. The results of the two 2021 online Workshops on Mackerel, Horse Mackerel and Hake Eggs Identification and Staging (WKMACHIS) and on Adult Egg Production Methods Parameters estimation in Mackerel and Horse Mackerel (WKAEPM) were discussed, with the subsequent enhancements and recommendations proposed during these workshops outlined in the workshop reports (ICES, 2022 a,b) and also incorporated into both of the WGMEGS manuals (ICES 2019a, b). Although the broad planning of the 2022 survey was undertaken during the 2021 planning meeting and detailed in the WGMEGS 2021 report, the provisionally agreed plan required additional intersessional refinements. The settled plan for the 2022 survey has been included as an annex in the latest version of the WGMEGS Manual for the Mackerel and Horse Mackerel Egg Surveys (ICES SISP 6, 2019a). In 2022, the survey once again faced significant challenges with regards to its ability to provide adequate geographical and temporal coverage given the limited vessel resources at our disposal. In 2022, Portugal, Spain (IEO and AZTI), Ireland, UK/Scotland, the Netherlands, Germany, the Faroe Islands, and Norway participated in the egg survey in the western and southern areas. Denmark and UK/England, with some additional assistance from Norway surveyed the North Sea as a single-pass DEPM survey. This is the first time in many years that all surveys have been completed in the same year. In 2022, the survey was split into six sampling periods. The final period ended in late July. Waters west and southwest of Portugal were surveyed in period 2 only. The Cantabrian Sea was sampled in periods 3–5 while Biscay was sampled in peri

Global studies imply that cephalopods have benefited from climate change. However, in most areas, species-specific long-term cephalopod data sets do not exist to support this implication and to analyse the response of cephalopods to environmental changes. Our results illustrate that historical studies, in combination with recent data sets, can fill this gap, enabling descriptions of ecological changes over a long time. We show substantial changes in the cephalopod biodiversity of the North Sea at species level over the past 100 years. Some species, which seemed to migrate into the North Sea only for spawning or foraging in the nineteenth century, occur permanently in the North Sea nowadays. This applies, for example, to the loliginids Loligo forbesii and Alloteuthis subulata. The ommastrephids Todaropsis eblanae and Illex coindetii, now constantly present as well, had been described only as accidental migrants 100 years ago.

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 examina-tion of changes in fish distribution and relative abundance. The group also promotes the stand-ardization 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.

The Working Group on DATRAS Governance (WGDG) aims to align the Database of Trawl Surveys (DATRAS) for the different surveys, to evaluate the database using guidance developed by Data and Information Group (DIG), to oversee, align and advise on requests for further development of DATRAS, and to provide a platform for end-user feedback. WGDG consists of representatives of ICES working groups delivering data to DATRAS: the Baltic Inter-national Fish Survey Working Group (WGBIFS), the International Bottom Trawl Survey Working Group (IBTSWG), and the Working Group on Beam Trawl Surveys (WGBEAM), as well as representatives of ICES Data Centre and of DIG. This report contains the main results of the past year’s meetings. The focus in this reporting period (June 2021-May 2022) has, as in previous years, been on alignment of DATRAS over different surveys, the main output being the implementation of the generic DATRAS format for submission across surveys. The implementation of the sub-mission was smooth, the communication of the changes to end-users can still be improved.

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 o

The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the national contributions on the results of the surveys conducted in 2021 together with time series covering all survey years, problems encountered, data quality checks and technological improvements as well as the planning for survey activities for 2022. In total, 19 surveys covering 25 functional units (FU’s) in the ICES area and 1 geographical sub- area (GSA) in the Adriatic Sea were discussed and further improvements in respect to survey design and data analysis standardization and the use of recent technologies were reviewed. Due to the COVID-19 pandemic there were minimal disruptions to survey operations where one survey was not completed (GSA 17). A trial trawl Nephrops survey offshore Portugal was carried out on the new research vessel. Preliminary work on how to measure burrow system size was presented using high definition (HD) and standard definition (SD) image data. Further work on comparison of SD and HD indi- cates the change to HD system mounted with a different camera angle was not significantly different for two survey areas (FU 16 and FU 20-21). Automatic burrow detection based on deep learning methods continues to show promising re- sults where datasets from multiple institutes were used. The working group members have agreed to draft a roadmap for automatic system technology requirements with links to the Work- ing Group on Machine Learning in Marine Science (WGMLEARN) and current researchers. The working group is progressing plans for an international Nephrops Underwater television (UWTW) database to be established at the ICES Data Centre. End-users of UWTV datasets for epifauna reporting presented their work and showed the potential for adding value to the survey data, where many of the institutes are involved in providing data for similar research purposes

Makrelbestanden i Nordatlanten har gennem de seneste år ændret sig dramatisk, både med hensyn til bestandskomponenterne, bestandsstørrelsen og ikke mindst makrellens udbredelse. Da makrellen desuden er en bestand med et ganske stort udbredelsesområde og med meget stor international interesse, er det vigtigt, at Danmark styrker kapaciteten og vidensgrundlaget indenfor denne bestand for at kunne yde indflydelse på de forvaltningsmæssige beslutninger. I 2020 blev der landet lidt over 1 mio. tons makrel i alt, og af dette var de danske landinger på lidt over 35.500 tons. Projektets formål har været at forbedre bestandsvurderingen og forvaltningen af makrel med fokus på makrellens Nordsøkomponent, hvor der især er en mangelfuld viden omkring udbredelse og biologi. Dette er blevet gjort ved at opbygge viden og gennemføre fire danske trawltogter (2018, 2019, 2020 og 2021) målrettet makrel i Nordsøen, som skal kombineres med de i forvejen gennemførte trawltogter fra det nordlige Atlanterhav. Resultaterne fra de danske trawltogter er blevet præsenteret hvert år til WGIPS og WGWIDE, som er de ICES-arbejdsgrupper, der har ansvar for hhv. makreltogterne og bestandsvurderingen af makrel. Som en del af projektet er der gennemført forsøg med at udvikle en multibeamsonar, der kan registrere de makrel, der søger under det pelagiske trawl under trækket. Projektet har også forsøgt at forbedre de kommercielle biologiske indsamlinger ved at udvælge den del af flåden, der går målrettet efter de pelagiske bestande, for at få en målrettet indsamling på de danske fartøjer, der står for hovedparten af landingerne. Dette er især vigtigt, fordi en meget stor andel af det danske makrelfiskeri landes i udlandet. Som et supplement til de prøver, som fiskerne selv skal indsamle, har vi gennem NordMak-projektet fået et samarbejde op at køre med Skawinspection, som har givet mulighed for at benytte alternative data, som indsamles regelmæssigt af industrien. Her har vi un

The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the national contributions on the results of the surveys conducted in 2021 together with time series covering all survey years, problems encountered, data quality checks and technological improvements as well as the planning for survey activities for 2022. In total, 19 surveys covering 25 functional units (FU’s) in the ICES area and 1 geographical subarea (GSA) in the Adriatic Sea were discussed and further improvements in respect to survey design and data analysis standardization and the use of recent technologies were reviewed. Due to the COVID-19 pandemic there were minimal disruptions to survey operations where one survey was not completed (GSA 17). A trial trawl Nephrops survey offshore Portugal was carried out on the new research vessel. Preliminary work on how to measure burrow system size was presented using high definition (HD) and standard definition (SD) image data. Further work on comparison of SD and HD indicates the change to HD system mounted with a different camera angle was not significantly different for two survey areas (FU 16 and FU 20-21). Automatic burrow detection based on deep learning methods continues to show promising results where datasets from multiple institutes were used. The working group members have agreed to draft a roadmap for automatic system technology requirements with links to the Working Group on Machine Learning in Marine Science (WGMLEARN) and current researchers. The working group is progressing plans for an international Nephrops Underwater television (UWTW) database to be established at the ICES Data Centre. End-users of UWTV datasets for epifauna reporting presented their work and showed the potential for adding value to the survey data, where many of the institutes are involved in providin

The Workshop on the production of annual estimates of abundance of sensitive species (WKABSENS) met to define sensitive species, collate ICES assessments of abundance where these are available, and estimate indices of their abundance per swept-area where not, for the OSPAR area. The analyses identified 140 potentially sensitive species or species complexes, among which 10 are diadromous and three are coastal, 20 have uncertain species ID and nine were identified as sensitive in only one of the sources examined. Among the sensitive species and species complexes, there was sufficient data to provide abundance indices for 50 species, of which 16 had existing stock assessments whereas the workshop derived abundance estimates for the remaining 34 species from survey data. Three statistical modelling approaches (binomial, General Additive Models (GAMs) and VAST) and were explored and the final abundance indices were calculated using GAMs. The species were divided into stocks before estimating abundance indices where these could be identified from the spatial distribution of the species in the survey. The group considered that a similar analysis using data from additional surveys, commercial indices or data from bycatch observers can potentially provide improved abundance estimates for species with variable or low catchability, such as deep-water and pelagic species.

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 excepti

The workshop on the production of swept-area estimates for all hauls in DATRAS for biodiver-sity assessments (WKSAE-DATRAS) considered three groups of surveys for which data are sub-mitted to the Database of Trawl Surveys (DATRAS): various Beam Trawl Surveys, the Northeast Atlantic International Bottom Trawl Survey (Northeast Atlantic IBTS), and the North Sea Inter-national Bottom Trawl Survey (North Sea IBTS). All countries contributing to the above-mentioned surveys were represented by at least one par-ticipant during the workshop, apart from the Netherlands and Norway. The main objectives of the workshop were to establish tow-by-tow swept-area estimates for time-series as far back in time as possible, compare different approaches for the estimates of missing observations, and harmonize the resulting dataseries for biodiversity assessments. For all of the surveys considered, problems with data quality were detected. This included the Beam Trawl Surveys but was most pronounced for the North Sea IBTS. Outliers and potential erroneous data were listed for reporting back to the respective national institutes. In particular, missing observations or algorithms affected wing spread-based swept-area, which is needed in several applications. This workshop compared the Marine Scotland Science-MSS/OSPAR approach, which includes a data quality check for the information needed for the calculation of swept-area, and the DATRAS approach, which depends solely on correctly reported data from the national institutes. Larger data gaps were identified, in particular for several years of the North Sea IBTS. For those surveys, it is proposed that the best possible way forward at this moment is to use estimates based on the MSS/OSPAR approach. However, if dubious records (i.e. extreme outliers) were identified by the MSS/OSPAR and no other information was available, values (e.g. speed over ground or the depth at which a change from short to long sweeps should have happened) were taken f

The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the national contributions on the results of the surveys conducted in 2019 together with time series covering all survey years, problems encountered, data quality checks and technological improvements as well as the planned for survey activities for 2020., The Working Group on Nephrops Surveys (WGNEPS) is the international coordination group for Nephrops underwater television and trawl surveys within ICES. This report summarizes the national contributions on the results of the surveys conducted in 2019 together with time series covering all survey years, problems encountered, data quality checks and technological improve- ments as well as the planned for survey activities for 2020. In total, 19 surveys covering 25 func- tional units (FU’s) in the ICES area and 1 geographical subarea (GSA) in the Adriatic Sea were discussed and further improvements in respect to survey design and data analysis, standardiza- tion and the use of most recent technology were reviewed. A new survey summary template by FU/GSA has been developed and adopted for future re- ports, which shall allow the data end users to extract the most relevant information on the survey results in a more easy way. Necessary actions and reviewer comments were addressed on the draft version of the Series of ICES Survey Protocols (SISP). Similarly, the working group reviewed the specifications for a Nephrops underwater TV database to be established at the ICES data centre and agreed on fur- ther action on this issue. First results from field studies on behaviour aspects of burrow emergence using bottom cages monitored by an automated camera system and on short-range migration using acoustic tracking are now available. Comparison of standard definition (SD) and high definition (HD) indicates the change to HD system mounted with a different camera angle may affect the detection rate and may thus require a revision of bias correction factors. New image reviewing software allows an easier way of an- notation of burrows than previous mosaicking methods, which has further advantages for inter- preting the results from different counters and for providing quality assured material for deep learning methods. The WG members agreed to collect information on burrow diameter, Postprint (published version)

The Danish anchor seine is an efficient type of active fishing gear used globally. Knowledge of the gear and its operational performance is limited, but needed to ensure efficient fishing and appropriate management. During this study, a combination of GPS loggers, depth loggers, and cameras, were utilized to collect quantitative information about the geometry of the seine net and seine ropes during all stages of the fishing process, and to identify when fish enter the seine net. Measurements of the horizontal and vertical openings of the seine net indicated that gear geometry changed continuously during the fishing process. Underwater recordings from the net revealed that the majority of fish entered the seine net within the last quarter of the fishing period, and that fishermen are able to control the timing of increasing the retrieval speed to prevent losing fish late in the fishing process. Underwater recordings of the seine rope provided qualitative results indicating that interactions with the sea bed are relatively minor in nature.

We investigated fine-scale effects of environmental variables associated with habitat distribution for 4 size groups of Cape hakes, Merluccius capensis and M. paradoxus, using generalized additive models (GAMs) with a negative binominal error distribution. This study took place during the Namibian hake trawl survey of 2016, and was made possible for the first time in Namibia by collecting oceanographic information with a trawl-mounted instrument package concurrently with the catch data. Depth, geographical position, bottom oxygen and bottom temperature had the most pronounced effect on the catch rates of both hake species, whereas solar zenith angle representing diel effects and surface layer chlorophyll appeared to be less important. The explained deviance for the best models ranged from 71.4% for M. capensis to 92.7% for M. paradoxus between 43 and 57 cm in length. Differences in catch rates between species and size groups were most pronounced for bottom depth and bottom oxygen. The results show the potential value of trawl-mounted instrumental packages for the collection of reliable environmental data important in the study of environmental influence on abundance, catch rates and distribution, and in turn in the assessment and management of a resource

Danish seines and bottom trawls operate differently and have different catching processes. Both gears belong to the same legislative category in European fisheries, but different management strategies in other countries and criticism by fishers on grouping Danish seines and trawls together indicate disagreement on current gear classification. This study compared both gears in terms of their fishing characteristics and catches of commercial species based on 16 years of observer data. Danish seining is a specialised fishing method that targeted few species but with higher total catch rates than bottom trawlers. Bottom trawling is a more all-purpose fishing method that targets a larger number of species, and bottom trawlers use larger engines than Danish seiners. A generalised additive mixed model indicated that catch rates of flatfish are generally higher for Danish seines, and catch rates of roundfish species are higher for trawlers. The results do not directly suggest a separation of the gears in terms of legislation as the quantities of fish below current minimum size were similar, but for example future survival studies may reach different conclusions. Additional factors were found to be important in determining catches of both gears

The codend is generally presumed to be the place where the main selectivity of fish occurs in towed fishing gears, but other parts of the net have been found to contribute to the selectivity process of several invertebrate species. This means that conventional selectivity or survival studies may ignore the selectivity of net parts other than the codend for certain species. By attaching 12 small meshed collecting bags to different parts of a Danish anchor seine net and conducting normal commercial fishing activities, this study showed that there is a substantial escapement of fish and (especially) invertebrates from the forward parts of the seine net. For seven species of demersal fish, most fish escaped through the lower panel close to the codend. All invertebrate species were found in higher numbers in the collecting bags than in the codend where many organisms escaped in the lower panel of the wings or the belly. Mean levels of visible damage ranged from 1.00 to 3.25 for collected invertebrates and were similar for all gear parts. Common starfish (Asterias rubens), however, showed highest damage in the extension part of the net.