Report of the planning group on herring surveys (PGHERS)

Abstract

REVIEW OF LARVAE SURVEYS IN 2005/2006: At the time of writing two of the seven surveys in the North Sea remained to be carried out in January 2006. Results will be ready for the Herring Assessment Working Group (HAWG) meeting in March 2005. COORDINATION OF LARVAE SURVEYS FOR 2006/2007: In the 2006/2007 period, the Netherlands and Germany will undertake seven larvae surveys in the North Sea from 1 September 2005 to 31 January 2006. Germany will contribute a second vessel to the IHLS to ensure coverage in the Orkney and Buchan area, which has not been covered in recent years; this will also take place in the first half of September. Thus, with the combined effort of Germany and Netherlands an almost complete coverage of the main spawning grounds is achievable. The Baltic Sea Fisheries Institute will continue with the larvae survey in the Greifswalder Bodden area in 2006. NORTH SEA ACOUSTIC SURVEYS IN 2005: Six acoustic surveys were carried out during late June and July 2005 covering the North Sea and west of Scotland. The provisional total combined estimate of North Sea spawning stock biomass (SSB) is 1.9 million t, a decrease from 2.6 million t in 2004. The stock is dominated by the 2000 year class. Growth of the 2000 year class seems again to be slower than average: 96% is mature. The west of Scotland SSB estimate is 190,000 t (400,000 t in 2004); this is a substantial reduction from last years estimate. The surveys are reported individually in Annex 2. WESTERN BALTIC ACOUSTIC SURVEYS IN 2005: A joint German-Danish acoustic survey was carried out with RV “Solea” from 4 to 21 October in the Western Baltic. The estimate of Western Baltic spring spawning herring SSB is 197,700 t (192,100 t in 2004). A full survey report is given in Annex 3. MANUALS FOR ACOUSTIC AND HERRING LARVAE SURVEYS: The manual for herring acoustic surveys in ICES Divisions III, IV, and VIA will be reviewed and updated in 2006 by correspondence. Development of the equipment used, has been extensive in recent years: an extensive review is, therefore, required: there was not enough time to carry out this activity at the meeting. The manual for the International Herring Larvae Surveys south of 62° north has been reviewed and updated. Version 2 of the manual is attached in Annex 5. STATUE AND FUTURE OF THE FISHFRAME AND HERSUR DATABASE: The status of the HERSUR database has not changed since 2005. Only Denmark has uploaded new data. Three countries have uploaded aggregated (“stage 3”) data in the Fishframe database. The international data set was completed by extracting national input data from the excel sheet used so far. The calculation, aggregation and reporting procedures on uploaded data of 2003, 2004 and 2005 was tested against the old procedure. The minor differences found were caused by differences in precision. It was decided that the Fishframe stage 3 module will be used to aggregate data from the 2006 surveys at the next meeting in 2007. To ensure that all countries confirm to same methods in stage 2, a group to design the user requirement specifications should be formed and meet during 13–14 June 2006 at DIFRES in Copenhagen. SPRAT: Data on sprat were available from RV “Walther Herwig” III, RV “Tridens” and RV “Dana”. The total sprat biomass was estimated as 562,000 t in the North Sea (up from 360,000 t in 2004) and 59,800 t in the Kattegat (up from 15,000 t in 2004). The present data suggest that sprat abundance is decreasing in the south and the distribution limit might therefore have been reached. COORDINATION OF ACOUSTIC SURVEYS IN 2006: Six acoustic surveys will be carried out in the North Sea and west of Scotland in 2006 between 25 June and 30 July. Participants are referred to Figure 4.4.1 for indications of survey boundaries. “Tridens” and “Walther Herwig” will cover the area between 52º and 57º together with interlaced transects. A survey of the western Baltic and southern part of Kattegat will be carried out by a German research vessel in October. LARVAE SURVEY SAMPLER: In the sampling period 2004-2005 the Netherlands changed from a Gulf III to a Gulf VII plankton torpedo. The Gulf VII seems to perform better in that the oblique hauls show a sharp ‘V’-shape. Possible differences between these two sampling devices will be investigated by sampling simultaneously with the Gulf III and Gulf VII during the September 2006 survey. A special set-up will be tested and improved during a survey in May targeting spawning horse mackerel in the southern North Sea. If the tests during the May survey prove successful, the apparatus will be used during the herring larvae survey in September 2006 to obtain a set of intercalibration hauls. REVIEW OF THE AGE READING WORKSHOP AT THE ARCHIPELAGO RESEARCH INSTITUTE ON THE ISLAND OF SEILI, FINLAND ON 6–JUNE 2005: Thirty-five participants from 25 countries attended the Age Reading Workshop to identify present problems in herring age determination, improve the accuracy and precision of age determinations and spread information of the methods and procedures used in different ageing laboratories working with herring. The main conclusion was that it is recommended that regular otolith exchanges take place between institutes in order to detect precision drift in the age estimations. EVALUATING THE POTENTIAN OF THE TORRY FISH FAT METER FOR MEASURING LIPID CONTENT OF HERRING AT SEA: Deborah Davidson from the University of Aberdeen gave a presentation of her ongoing PhD study examining the fat content in herring (see working document in Annex 7). The overall aim of the field study in 2006 is to determine whether lipids impose a threshold on the onset of maturation in North Sea herring. PGHERS recommends that in the 2006 North Sea acoustic surveys, all participants take a student from Aberdeen University to make measurements of the fat content of herring.