Report on the Herring Assessment Working Group for the Area South of 62ºN (HAWG)

Abstract

The Herring Assessment Working Group (HAWG) met in ICES headquarters from 9 to 18 March 2004. The main terms of reference were to assess the status of and to provide catch options for the North Sea autumn-spawning herring stock in ICES Division IIIa, Sub-area IV and Division VIId, the herring stocks in Division VIa and Subarea VII, the stock of spring-spawning herring in Division IIIa and Subdivisions 22-24 (Western Baltic), and the sprat stocks in Sub-area IV and Divisions IIIa and VIId,e. The WG reports on the status of all of the stocks (8 herring and 3 sprat stocks). Analytical assessments were only carried out on 4 out of the 11 stocks the WG was requested to examine and of these four analytical assessments of only three of the herring stocks were accepted last year. This year the working group adopted the proposed ACFM methodology of allocating assessments to categories (The Benchmark - Update assessment system). Of the different stocks to be considered by the HAWG, the NSAS-stock was on the Observation list, the WBSS was to have a benchmark assessment and herring in VIa, VIIa, Celtic and sprat update assessments. During the progress of the work, the WG agreed to redefine the assessment of WBSS stock into an update assessment as no new relevant information was available and the assessments on Irish Sea herring, herring in VIaS, VIIb and sprat in the North Sea, as experimental assessments. The other stocks were considered as update assessments. For Irish Sea herring, an additional two-stage biomass model was used to assist exploration of the stock dynamics. The assessments of the autumn spawners in the North Sea, VIaN and the Western Baltic spring spawners (WBSS), are consistent with those presented last year, resulting in little changes in the perception of the stocks. With regard to the model used for the assessment of all herring stocks, namely ICA, concern has been raised about the instability in the selection patterns at older ages which would affect the stock estimates in the early part of the time series. The WG examined the performance of ICA on North Sea herring and Western Baltic Spring Spawners with another regularly used assessment model, XSA. The two models gave very similar perceptions of the state of the stock and the WG felt that the use of the ICA model is still appropriate. This also maintains consistency with assessments in previous years. Most of the stocks assessed are considered within safe biological limits. Corresponding catch predictions are provided in options tables for 2005, where possible by fleet. A number of data revisions have been applied to the assessment input data set for North Sea and WBSS at this year’s WG, as total catch and catch-at-age have been updated for the catch years 1995-2002. The catch series for West of Scotland (ViaN) herring were extended back to 1957, with no changes in the perception of the status of the stock compared to the 2003-assessment for the years 1976-2002. There is still a need for better input/sampling data for some stocks, and in other stocks there is a lack of fishery independent data. Though few estimates of discards were available, the amount of discards for most fisheries was regarded as insignificant. The Stock Annexes of the Quality Control Handbook have been drafted and are attached to the HAWG report. In many cases these are incomplete as there is a large amount of information needed for each and they take a considerable amount of time to compile. For stocks without an accepted assessment, general elements (stock definitions, fisheries and ecosystem aspects) are presented. For VIaN herring, the inclusion of the longer time-series of catches including a period with higher stock productivity and higher biomass, resulted in the WG reviewing the support for the proposed reference points for that stock. The WG considered that the proposed Blim of 50,000t and a Bpa of 75,000t are suitable limits and reference points. The management arrangement for North Sea herring, adopted in 1998 by EU and Norway, was largely based on medium-term simulations made in 1997. Since this is 7 years ago, and the management regime only became effective recently, the WG found it appropriate to reinvestigate the harvest control rules with new simulations. The simulations and the results are presented in the report. Two formal requests from the EU-Commission to advise on TACs for herring in the Skagerrak/Kattegat-area, were considered by the HAWG