Ices Wkmixher Report 2018
Total Page:16
File Type:pdf, Size:1020Kb
ICES WKMIXHER REPORT 2018 ICES ADVISORY COMITTEE ICES CM 2018/ACOM:63 Report of the workshop on mixing of western and central Baltic herring stocks (WKMixHER) 11 – 13 September 2018 Gdynia, Poland International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer H. C. Andersens Boulevard 44–46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk [email protected] Recommended format for purposes of citation: ICES. 2018 Report of the workshop on mixing of western and central Baltic herring stocks (WKMixHER). 11–13 September 2018, Gdynia, Poland. ICES CM 2018/ACOM:63. 39 pp. The material in this report may be reused for non-commercial purposes using the rec- ommended citation. ICES may only grant usage rights of information, data, images, graphs, etc. of which it has ownership. For other third-party material cited in this re- port, you must contact the original copyright holder for permission. For citation of da- tasets or use of data to be included in other databases, please refer to the latest ICES data policy on ICES website. All extracts must be acknowledged. For other reproduc- tion requests, please contact the General Secretary. The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council. © 2018 International Council for the Exploration of the Sea ICES WKMixHer REPORT 2018 | i Contents Executive summary ................................................................................................................ 1 1 Introduction .................................................................................................................... 2 1.1 Terms of reference ................................................................................................ 2 1.2 General background ............................................................................................. 2 1.3 Structure of the report .......................................................................................... 3 2 Review and report on recent research on mixing of western Baltic spring spawning herring (WBSSH) and central Baltic herring (CBH) stocks and potential implications of such mixing for the assessment and management of both stocks (Tor a) ............................................................................ 4 2.1 Review of methods and materials ...................................................................... 4 2.2 Discrimination of Western Baltic Spring Spawning (WBSSH) and Central Baltic Herring (CBH) based on growth................................................ 4 2.3 Potential impact of stock mixing on the herring catches in the subdivisions 24-25. What if we could discriminate by growth? .................... 6 2.4 Otolith shape analysis as a tool for stock separation - North Sea/Skagerrak ........................................................................................................ 9 2.5 Otolith shape analysis as a tool for stock separation – Baltic example ............................................................................................................................... 10 2.6 Contribution of an inshore nursery area to the Atlantic herring (Clupea harengus) population in the Western Baltic Sea based on otolith chemistry ................................................................................................. 13 2.7 Population status of infected herring in the Baltic as an indication of herring migrations .............................................................................................. 14 2.8 Literature review of recent research on mixing of western Baltic spring spawning herring (WBSSH) and central Baltic herring (CBH) stocks .................................................................................................................... 17 2.9 Summary of NMFRI research on genetic differences in herring .................. 18 2.10 New genetic analyses to determine stock structure and mixing .................. 19 2.11 Assessment model of western & central Baltic herring, which includes exchange of fish between both stocks (migrations) ........................ 21 3 Coordinated plan for collection and analysis of relevant data to quantify herring stock mixing in the western and central Baltic (ToR b) ......................................................................................................................................... 23 3.1 Short-term plan ................................................................................................... 23 3.2 Long-term plan ................................................................................................... 24 4 Conclusions and recommendations ......................................................................... 27 5 References ..................................................................................................................... 29 Annex 1: List of participants............................................................................................... 32 ii | ICES WKMixHer REPORT 2018 Annex 2: Preliminary results for genotyping of samples of spawning herring from the Polish coast ................................................................................................... 33 Annex 3: Otolith shape analysis based on preliminary genotyping of samples of spawning herring from the Polish coast ............................................. 36 ICES WKMixHer REPORT 2018 | 1 Executive summary The workshop on mixing of western and central Baltic herring stocks (WKMixHER), chaired by Valerio Bartolino, Sweden, and Jan Horbowy, Poland, met in Gdynia the 11– 13 September 2018. The meeting was attended by altogether 12 participants, including experts from Germany, Denmark, Latvia, Poland, Lithuanian, Norway and Sweden cov- ering expertise from herring biology, biological data collection and analysis, genetics, oto- lith shape analysis and stock assessment. The aims of WKMixHER were to review recent research and available methods to dis- criminate western Baltic spring spawning herring and central Baltic herring in mixed catches, evaluate potential implication of mixing for the assessment, develop a coordi- nated plan to collect and analyse relevant data to quantify the mixing. Different methods for herring stock identification were reviewed at the workshop based on old and on-going analyses carried on samples from the western and central Baltic Sea. Analyses presented at the meeting suggested that interpretation of the ToRs for this work- shop is actually conditioned by a better understanding of the central Baltic herring stock structure. The central Baltic herring is known to be dominated by a northern and a south- ern component, but for the first time at the workshop it was shown how the latter actually shares numerous characters with the adjacent western Baltic herring stock. Its growth and otolith shape are more similar to those of herring of western origin than to fish from the northern component. Based on only growth, a high proportion of fast growing herring is found in SD25 and especially in the westernmost rectangles but it remains unclear if those fish are part of the southern component of the central Baltic or if they are the results of extensive mixing with the western Baltic herring. Preliminary analyses suggest a progressive genetic differentiation along the entire south- ern Baltic coasts from SD24 to SD26 rather than a clear cut division between different assessment units. Soon it became clear that the problem of separating the Central Baltic herring stock from the western Baltic spring spawning herring stock is related to under- stand if the southern component should be considered together with the western Baltic herring, maintained with the central Baltic herring, or if it should be considered sepa- rately. Depending on the task, the methodologies reviewed for stock identification could be promising or insufficient. Clarify the stock structure of the central Baltic herring was not the objective of this work- shop, but the issue steered the proposal for a two years coordinated plan of sampling which was delineated at the workshop with the objective to validate herring assessment units and look for operational methods to separate them in mixed catches. 2 | ICES WKMixHer REPORT 2018 1 Introduction 1.1 Terms of reference The Workshop on mixing of western and Central Baltic herring stocks (WKMixHer), co- chaired by Valerio Bartolino (Sweden) and Jan Horbowy (Poland), will be established and will meet in Gdynia, Poland, 11–13 September 2018 to: a) Review and report on recent research on mixing of western Baltic spring spawn- ing herring (WBSSH) and central Baltic herring (CBH) stocks and potential impli- cations of such mixing for the assessment and management of both stocks b) Develop a coordinated plan for collection and analysis of relevant data to quan- tify mixing of both herring stocks in the western and central Baltic. Consider anal- ysis of genetic data, growth rates, morphometrics and otolith shape analysis, infestation with parasites as natural tags, and other potential discriminants of herring populations. 1.2 General background The Western Baltic Spring Spawning herring (WBSSH) spawn in Spring in the western coastal areas of the Baltic Sea. During Summer, WBSSH migrate to Summer feeding grounds (June/July) out of the Baltic into the Kattegat, Skagerrak and