Report of the Workshop on Age Estimation of Norwegian Spring Spawning Herring Between, Norway, Denmark, Iceland and the Faroe Islands (WKNSSAGE)
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ICES WKNSSAGE REPORT 2015 ACOM/SCICOM STEERING GROUP ON INTEGRATED ECOSYSTEM OBSERVATION AND MONITORING ICES CM 2015/SSGIEOM:37 REF. SCICOM, ACOM, WGWIDE & WGBIOP Report of the Workshop on Age estimation of Norwegian Spring Spawning Herring between, Norway, Denmark, Iceland and the Faroe Islands (WKNSSAGE) 9–10 November 2015 Charlottenlund, Denmark 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. 2016. Report of the Workshop on Age estimation of Norwegian Spring Spawn- ing Herring between, Norway, Denmark, Iceland and the Faroe Islands (WKNSSAGE), 9–10 November 2015, Charlottenlund, Denmark. ICES CM 2015/SSGIEOM:37. 46 pp. For permission to reproduce material from this publication, please apply to the Gen- eral 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. © 2016 International Council for the Exploration of the Sea ICES WKNSSAGE REPORT 2015 | i Contents Executive summary ......................................................................................................................1 1 Terms of reference ..............................................................................................................2 2 Agenda and participation..................................................................................................3 3 Introduction ..........................................................................................................................3 4 Review the technical problems regarding age-reading of Norwegian spring spawning herring between Denmark, Norway, Iceland and the Faroe Islands regarding the extra growth added in May-sample (ToR a) ..................................................................................................................................................4 4.1 Interpretation of the season and age dependent growth at the edge of the structure ...........................................................................................................5 4.2 Potential differences related to the use of otolith or scale for age determination .............................................................................................................7 4.3 Recommended future work.....................................................................................7 4.4 Conclusions and recommendations.......................................................................8 5 Analyse the problematic structures (otoliths/scales) from the IESNS- surveys (May-surveys) described by WGWIDE (ToR b) ..........................................9 5.1 Pre-workshop samples .............................................................................................9 5.1.1 Otoliths ...........................................................................................................9 5.1.2 Scales ............................................................................................................ 10 5.1.3 Issues regarding both structures ............................................................ 10 5.1.4 Conclusions ................................................................................................ 10 5.2 Workshop exercise.................................................................................................. 11 5.2.1 Material and methods .............................................................................. 11 5.2.2 Results.......................................................................................................... 12 5.2.3 Conclusions and evaluation of the exercise......................................... 14 6 Clarify the interpretation of annual rings in particular during spring/summer (ToR c) ................................................................................................... 15 6.1 Introduction ............................................................................................................. 15 6.2 Methods .................................................................................................................... 16 6.3 Conclusions and recommendations.................................................................... 21 7 Improve the protocol for age estimation of the applied structure (otolith or scale) (ToR d) ................................................................................................................ 22 7.1 Introduction ............................................................................................................. 22 7.2 Preparation and aging methods .......................................................................... 23 7.2.1 Preparation ................................................................................................. 23 7.2.2 Viewing of structures and images ......................................................... 24 ii | ICES WKNSSAGE REPORT 2015 7.2.3 Age determination criteria ...................................................................... 24 7.2.4 Factors affecting annual ring formation ............................................... 27 8 References .......................................................................................................................... 29 Annex 1: Agenda........................................................................................................................ 30 Annex 2: List of participants................................................................................................... 31 Annex 3: Results of the workshop exercise ........................................................................ 32 Annex 4: Edge development ................................................................................................... 38 Annex 5: Recommendations ................................................................................................... 42 ICES WKNSSAGE REPORT 2015 | 1 Executive summary The workshop on age reading of Norwegian Spring Spawning herring (WKNSSAGE), chaired by Jane Aanestad Godiksen, met 9–10 November 2015 in Charlottenlund, Den- mark. The meeting was attended by 12 experts from four countries. WKNSSAGE was a request from WGWIDE to WGBIOP to review any technical problems regarding age- reading of Norwegian spring spawning herring between Norway, Denmark, Iceland and the Faroe Islands. In 2015 Norway sampled the same areas as the three other coun- tries during the IESNS-survey, and during the post-cruise meeting the differences be- tween the age distributions from trawl samples taken in the same area and period became apparent. For example, from one stratum the Norwegian samples were domi- nated by three age groups, while the age distribution from Denmark looked much more uni-modal. Also comparison of samples taken by Norway, the Faroe Islands and Iceland show age distributions, which are not comparable, and thus, ageing or sam- pling issues are likely to exist among all of the participating nations. As a result, WGWIDE approached WGBIOP with a request for a fast-track workshop between age readers to address any potential issues related to the age determination of NSS herring. Denmark and the Faroe Islands are ageing NSS herring by reading their otoliths, while Norway and Iceland use scales. To establish a common understanding of how both structures appear and are interpreted the workshop was initiated by examining some pre-annotated scales and otoliths. Concerns over the interpretation of the edge were addressed and there appeared to be very little disagreement in the interpretation of the growth zones in either structure. Thereafter an exercise containing otoliths and scales from the same fish was prepared in WebGR, the actual structures were also available to the readers. The results showed a low level of agreement (52%) between age read- ings and a general trend appeared where the scales were estimated to be one year older than the otoliths. This lead to an apparent loss of the strong year class of 2004. After reviewing the structures in plenary, it was clear that it was most often the first winter ring in the scale which was not clearly visible in the otolith. In order to review the problem in more detail a numerical analysis was attempted utilizing the measurements extracted from WebGR. A number of shortcomings were noticed when using this ap- proach to identify potential problem areas in the age interpretation. The problems could be associated with mixing of subpopulations and/or stocks. WKNSSAGE concluded that the different ages obtained from scale and otolith read- ings could be due to a number of issues relating to identification of the first winter ring and age interpretation of older fish, confounded by stock mixing issues. Final conclu- sions cannot be reached based on the samples from this workshop. We believe the sam- pling and stock mixing issues should be addressed separately by WGWIDE. Overall, WKNSSAGE recommend that the Workshop on Age estimation of Norwegian Spring Spawning Herring (Clupea harengus) (WKARNSSH) 2017 consider the short- comings of the present workshop and develops an ageing protocol that contain robust procedures for a quality check. The above mentioned ageing issues should be ad- dressed in full based on a larger