Vis in het Eems-estuarium

De hier voorliggende korte rapportage betreft een bundeling van de resultaten van verschillende vismonitoring surveys, zoals deze worden uitgevoerd door Wageningen Marine Research en BioConsult in het Eems-estuarium. Deze rapportage is opgesteld in opdracht van Rijkswaterstaat WVL en zal door Rijkswaterstaat worden gebruikt bij het samenstellen van een jaarlijkse rapportage over het Eems-estuarium in het kader van het programma Eems-Dollard 2050 (ED2050)

Second Workshop on Estimation with the RDBES data model (WKRDB-EST2; outputs from 2020 meeting)

This report shows how the new RDBES that is currently in development will be better able to support the recast EU Data Collection Framework (Regulation (EU) 2017/1004) than the existing RDB. The RDBES is an essential platform for MS and RCGs to fulfil their obligations towards documenting and improving data quality and designing and implementing regional sampling designs. The evaluation of data precision was performed using two complementary techniques. For relatively simple sampling designs it is possible to use analytical functions to calculate the precision (or a related statistical measure such as variance) of a statistical estimate. These calculations and implementations of them in R code are presented in this report. For more complicated sampling designs, the use of analytical functions is usually not feasible. In these cases, it is necessary to evaluate precision using numerical techniques, the main one of which is bootstrapping. This report discussed when bootstrapping is appropriate and gives several worked examples describing how bootstrapping can be applied in different cases. The evaluation of bias is a difficult subject and is hard to quantify. The approach followed in this report was to build on the previous work available in the ICES literature and identify and enumerate the main common sources of bias in catch sampling programs they describe. The information was collated and an evaluation performed as to whether data stored using the RDBES data format and reports issues from them can inform about the potential for bias in catch estimates. A set of example reports was coded that demonstrates the utility of the RDBES in relation to bias issues and can already help member states to identify how deviations in their sampling programmes and sampling variability may potentially lead to bias in their catch estimates

The Third Workshop on Population of the RDBES Data Model (WKRDB-POP3)

The aims of this workshop were to explain the data model developed for the commercial fisheries Regional Database and Estimation System (RDBES), assist in populating it with real data for the second test data call for the RDBES, and encourage participants to take part in ongoing testing of the RDBES data submission system. This report documents the progress that participants have done to prepare their institutes for future use of the RDBES system. Some issues with data conversion have been identified and are documented in this report. None of the identified issues are thought to be serious impediments to moving forward with the RDBES development according to the roadmap decided by the Steering Committee of the Regional Fisheries Database in 2020. The RDBES Core Group (the group of people developing the RDBES data model) and ICES Data Centre will look at the results of this workshop and either respond to individual questions or adapt the data model and documentation as required. The workshop concluded and reported before the deadline of the test data call. For a complete test of the data model, all participants were encouraged to complete the data call. A report on the degree of completion of the data call may be expected from WGRDBESGOV which convenes after the data call deadline

Workshop on Raising Data using the RDBES and TAF (WKRDBESRaiseTAF; outputs from 2022 meeting)

41 páginasThe Workshop on Raising Data using the RDBES and TAF (WKRDBES-Raise&TAF) met online (26–30 of September 2022) to evaluate the use of the Regional Database and Estimation System (RDBES) format to reproduce the 2022 InterCatch input and output, identifying a Transparent Assessment Framework (TAF) structure to organize the intermediate steps and to propose standardized output formats. The main outcomes of WKRDBES-Raise&TAF were: · RDBES provides sufficient support for current national estimation protocols. However, some minor issues were reported that hampered an exact reproduction of the estimates. Therefore, adaptations of the data model should not be excluded completely. · All the input to stock assessment that InterCatch currently provides, could be reproduced. The participants started from the current stock extracts that can be downloaded from InterCatch. · A workflow was proposed with a national TAF repository for each country, a stock estimation repository and a stock assessment repository. The intermediate output of those repositories will be stored in an ‘intermediate output database’ and depending on the user role, you will get access to the relevant stages in this workflow. · The following requirements for the standard output formats were defined: they cannot be more restrictive than the InterCatch input and output format; they should present measures of uncertainty and sample sizes (for national estimates) and should have a configurable domain definition (for national estimates). Despite those successful outcomes, the current plan for transition to an operational system was concluded to be too optimistic. WKRDBES-Raise&TAF therefore recommends to the Working Group on Governance of the Regional Database and Estimation System (WGRDBESGOV) to revise the roadmap and allow RDBES to be in a test phase also for 2023. WKRDBES-Raise&TAF felt the need to test the proposed workflow on a small scale and therefore recommends to the WGRDBESGOV to arrange a workshop where two stocks (pok.27.3a46 (Saithe (Pollachius virens) in Subareas 4, 6 and Division 3.a (North Sea, Rockall and West of Scotland, Skagerrak and Kattegat) and wit.27.3a47d (Witch (Glyptocephalus cynoglossus) in Subarea 4 and Divisions 3.a and 7.d (North Sea, Skagerrak and Kattegat, eastern English Channel)) will be set up to go through the whole flow.Peer reviewe

Logboekanalyse schubvisvisserij IJssel- en Markermeer 2016-2020

Het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) is in het kader van de Visserijwet verantwoordelijk voor een duurzame visserij op het IJsselmeer en Markermeer. Om meer inzicht te krijgen in de onttrekking van snoekbaars, baars, blankvoorn, brasem en bot uit het IJsselmeer en Markermeer en de inspanning die daarvoor gepleegd wordt, zijn beroepsvissers sinds 2015 verplicht vangst- en inspanningsregistraties aan te leveren voor hun schubvisaanlandingen. Deze registraties dragen bij aan het toewerken naar en handhaven van een duurzame visserij. In deze briefrapportage wordt een overzicht gegeven van vangstregistratie van 2016 tot en met 2020. Dit is daarmee een vervolg op de rapportage uit 20201, waarin de registratie t/m periode 1 van 2019 werd besproken. Het doel van deze rapportage is om aan de hand van beschrijvende statistieken een beeld te schetsen van de visserij in het Markermeer en IJsselmeer

Survival probabilities of thornback and spotted rays discarded by beam trawl and flyshoot fisheries

Elasmobranchs (i.e. sharks, skates and rays) play an important role as predators in marine ecosystems. In the last century the abundance of several skates and rays in the North Sea declined. Their specific life-history traits, i.e. being long-lived, showing slow growth, late sexual maturity and producing a small number of young per year, make them vulnerable to fishing, pollution and changes in essential habitats, especially spawning and nursery areas. Since 2010 a recovery in the abundances of some species is observed. Landings of skates and rays in European waters are generally managed by a group-TAC, meaning several species are managed under a single Total Allowable Catch (TAC). In the North Sea this group-TAC applies to thornback (Raja clavata), blonde (Raja brachyura), spotted (Raja montagui) and cuckoo ray (Leucoraja naevus). Landings of starry ray (Amblyraja radiata) and common skate (Dipturus sp.) are prohibited. In Dutch fisheries, skates and rays are mainly caught as by-catch in the mixed demersal fishery for flatfish, with landings dominated by thornback ray. For these species the rays below minimum landing size and catches that exceed the vessel’s weekly trip limits are discarded. Since 2019 this practise of discarding has been restricted for all quota regulated species, including rays, by the implementation of a landing obligation under the Common Fisheries Policy (European Union, 2013). The objective of the landing obligation is to create an incentive for fishers to avoid unwanted bycatches and thereby reduce discards rates. The European commission granted a temporary ‘high survival’ exemption for rays and indicated that for this exemption to be renewed or extended beyond 2023, knowledge gaps regarding discards survival probabilities of rays, as laid out in the “Roadmap skates and rays”, need to be filled. The current study therefore aims to contribute to this roadmap by filling main gaps in our knowledge on the survival probability of rays when discarded by the most important Dutch demersal fisheries. Beam trawl and flyshoot fisheries are quantitatively the main contributors to ray catches by Dutch demersal fisheries with thornback and spotted ray as main species. These two métiers and species were therefore selected for the discards survival experiments. We conducted five trips with a beam trawler during which 184 thornback and 140 spotted rays were sampled and four trips with a flyshooter during which 134 thornback and 28 spotted rays were sampled. Survival probabilities were measured by captive observation of these rays up to 25 days post-capture. Control rays were used to separate potential effects of the experimental procedures on mortality from fisheries-induced mortality. All fishery operations were conducted in the southern North Sea (ICES division 27.4.c) and in the English Channel (ICES division 27.7.d) according to the regular commercial practices of the fishing vessels. Trips were allocated to different quarters over the year to account for the effect of variable environmental and fishing conditions on discards survival. Operational and environmental conditions during sea trips were recorded. In this study we established the following discards survival probabilities (95% CI): • 45.5% (37.9-54.5) for spotted ray discarded by tickler chain beam trawl fisheries with 80 mm cod-end meshes; • 49.6% (42.9-57.4) for thornback ray discarded by tickler chain beam trawl fisheries with 80 mm cod-end meshes; • 77.6% (63.3-95.2) for spotted ray discarded by flyshoot fisheries with 80 mm cod-end meshes; • 81.0% (74.4-88.2) for thornback ray discarded by flyshoot fisheries with 80 mm cod-end meshes. The experimental procedures did not cause any mortality since all control rays survived the experiments. All mortality among sampled rays can thus be considered to be fisheries induced. Survival probability was higher for rays discarded by flyshoot fisheries compared to beam trawl fisheries. Survival probability of discarded rays decreased with increasing seawater temperature and some evidence for decreasing survival with increasing catch processing time was found. Species and body length did not affect survival probability. Survival probability was highest for rays that were landed on deck in good condition. To further increase survival probability it is recommended to keep catch processing time as short as possible and to focus on gear modifications that reduce stressors inflicted upon fish during the catch and hauling process to increase the proportion of rays that is landed on deck in good condition. In addition, we recommend to pursue reduction of fishing mortality among rays by reducing the amount of caught rays by improved selectivity of fishing gear and by actively avoiding fishing grounds where rays occur in high densities

Working Group on Governance of the Regional Database and Estimation System (WGRD-BESGOV; outputs from 2021 meeting)

The Working Group on Governance of the Regional Database & Estimation System (WGRDBESGOV) provides the governance function for both the existing Regional Database (RDB) and the new Regional Database & Estimation System (RDBES) that is currently in development. It is composed of representatives from ICES member countries and EU Regional Coordination Groups (RCGs). In this report the WGRDBESGOV reviews the RDBES developments performed during 2021 and plans for the work required in 2022 and beyond. It also considers how RDB data has been used and proposes changes required to the current Data Policy