Report of the Working Group on the Assessment of Mackerel, Horse Mackerel, Sardine and Anchovy (WGMHSA) [6-15 September 2005 Vigo, Spain]
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The Working Group on the Assessment of Mackerel, Horse Mackerel, Sardine and Anchovy (WGMHSA) met in Vigo from 5-16 September, to assess and provide catch options for four different pelagic species widely distributed in the Northeast Atlantic Ocean. The WG reports on the status of all 7 stocks (see Fig. 0.1 for stock definitions), and in case of Sardine also on the status of the species distributed outside current stock definitions. This year a benchmark analytical assessment is available for Anchovy in Biscay and update analytical assessments are available for Northeast-Atlantic Mackerel and Sardine in VIIIc and IXa. Western Horse mackerel is in a benchmark year, so an in-depth exploratory analysis was carried out using several models (with different assumptions) as well as exploring the signals in the input data. Southern horse mackerel and Gulf of Cadiz anchovy assessments are still in a developmental stage, whilst no assessment was possible for North Sea horse mackerel. Northeast-Atlantic (NEA) Mackerel. This species is distributed in the whole ICES area and currently supports one of the most valuable European fisheries (with more than 600 kt annual landings). Mackerel is fished by a variety of fleets (ranging from open boats using hand lines on the Iberian coasts to large freezer trawlers and Refrigerated Sea Water (RSW) vessels in the Northern Area. The stock is historically divided into three components, with the North Sea component considered to be over fished since the late 1970s, and the Western component contributing the vast majority of biomass and catch to the combined stock. The quality of sampling data remains good. There is an extensive exploration section examining the trade offs in assessing the NEA mackerel stock with the available data and model formulations. This year the issue of accuracy of the catch data has been addressed, and indicates that data on both the accuracy of landings and estimates of total discards is inadequate. The WG carried out an update assessment applying the same approach as accepted by ACFM last year. The assessment indicates that the declining trend of the stock has not continued, but that F in 2004 was above Fpa and outside the management agreement. The exploration exercise concludes that although the trend in SSB and F and the level of F can be estimated without bias from the existing data, that the true level of SSB cannot be estimated without knowledge of the level of unaccounted mortality.Horse Mackerel. Following from the redefinition of the stock boundaries last year, much work had been carried out intersessionally, in compiling extended data series for western and southern horse mackerel. For North Sea horse mackerel effort was applied this year to try and understand why any attempted assessments performed so poorly. The data exploration showed inconsistent signals in the catch at age data and a survey index, which may be missing an important component of the stock due to seasonal migration. An in depth exploration was carried out for western horse mackerel. These analyses showed (with the available data i.e. no independent measure of stock size), that there had most likely been a change in fishing pattern in the mid 90’s, that the SSB followed the growth of the exceptional 1982 year class, and that in 2004 this is at a level around that in 1982. Although large uncertainty surrounds the estimates of stock parameters, the analyses were more stable and indicated strong recruitment of the 2001 year class which may have halted the declining trend of the stock. An exploratory analyses was conducted for southern horsemackerel. This analysis suffers from conflicting signals between surveys and as for western horse mackerel the absence of an SSB index. None the less the data exploration indicates a declining SSB since the late 90’s with stable F. Sardine is assessed only in part of the distribution area: in VIIIc and IXa. Stock structure is currently under investigation. An update assessment was performed. This assessment showed a small decrease in the SSB due to the waning influence of the 2000 year class, but that the SSB is about average. The assessment also indicates a large incoming recruitment (2004 year class). However even at this level of SSB the stock is more dependent on incoming recruitment than in the 1980’s. Anchovy is a short-lived species, showing large fluctuations in biomass. This is driven by recruitment which in turn might be driven by a combination of environmental factors. Catches consist mainly of 1- and 2-yr old fish. In 2005 there was a failure of the commercial fishery for the Biscay stock, and this prompted much intercessional work and meetings to be conducted before the WG. In addition this year the WG attempted a benchmark for Biscay anchovy, an annual ICA assessment, as performed in previous years, plus a seasonal one are presented as exploratory assessments, while a Bayesian implementation of the biomass dynamic model is proposed as the final assessment. There was coherence in the signals in the catch and survey data and new implementation of the assessment model overcomes some of the shortcomings of the previous approach. The overall outcome is that SSB is below Blim and recruitment at age 1 has been low since 2002. Without a recruitment index little can be said about the prognosis for the stock until the next acoustic and DEPM surveys in late Spring 2006. The assessment of Anchovy in Cadiz is developed further this year with a standardisation of the CPUE index. This exploratory assessment now gives a coherent picture of the development of the stock.
Contributors: Svein A. Iversen, Dankert W. Skagen
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