Working Group on Widely Distributed Stocks (WGWIDE)

Abstract

The Working Group on Widely Distributed Stocks (WGWIDE) reports on the status and considerations for management of Northeast-Atlantic mackerel, blue whiting, Western and North Sea horse mackerel, Northeast-Atlantic boarfish, Norwegian spring-spawning herring, striped red mullet (Subareas 6, 8 and Divisions 7.a-c, e-k and 9.a), and red gurnard (Subareas 3, 4, 5, 6, 7, and 8) stocks. Northeast-Atlantic (NEA) Mackerel . This species is widely distributed throughout the ICES area and currently supports one of the most valuable European fisheries. Mackerel is fished by a variety of fleets from many countries (ranging from open boats using handlines on the Iberian coasts to large freezer trawlers and Refrigerated Sea Water (RSW) vessels in the Northern Area). The assessment methodology was modified during the 2019 inter-benchmark process. The 2019 WGWIDE assessment was an update of the benchmarked assessment incorporating a new year for the catch information, for all surveys (egg survey, IESSNS survey and recruitment index) and for the RFID tagging recapture. After a strong increase from the late 2000s to 2014, the SSB has been declining since 2015, but remains at high levels (well above MSY Btrigger), The estimated fishing mortality has been steadily declining since the mid-2000s, and is now estimated to be close to FMSY. This decrease of the fishing mortality, while the stock has been sustaining high catches (consistently in excess to ICES advice) is explained by a succession of good recruitments, indicating a current high productivity for this stock. Blue Whiting. This pelagic gadoid is widely distributed in the eastern part of the North Atlantic. The assessment this year followed the Stock Annex based the conclusions from the Inter-Benchmark Protocol of Blue Whiting (IBPBLW 2016). The method for calculating mean weight at age for the preliminary (2019) was however changed, such that the observed values were used. Previously, a three year average was used. Most of the annual catches are taken in the first halfyear, which makes it possible to use preliminary catches for 2019 in the assessment. This is done to reduce the effect of potential biases from the single survey used for this assessment. The SSB of the stock is large but declining since 2018. F has been reduced in recent years, but is still above FMSY. Recruitments in 2017–2019 are estimated to be low, following a period of high recruitments. Western Horse Mackerel . This species is widely distributed throughout the Northeast Atlantic: it spawns in the Bay of Biscay, and in UK and Irish waters; after spawning, parts of the stock migrate northwards into the Norwegian Sea and the North Sea. The stock is assessed using the Stock Synthesis integrated assessment model. The 2019 assessment is an update of the benchmark assessment with the inclusion of the 2018 data. According to the assessment results, the 20154-2018 recruitment estimates are the highest observed since 2008 (and higher than the geometric mean estimated over the years 1983–2018). Fishing mortality since 2012 has been decreasing overall, dropping to low values in 2015–2018 due to lower catches and a reduced proportion of fraction of the adult population in the exploited stock; it is however currently above FMSY. SSB in 2017 was estimated as the lowest in the time-series, below the limit reference point and is just above in 2018. The updated assessment shows the same trend as the previous ones, but rescales the absolute level of SSB and F over the most recent decade and, although this years’ revision is smaller, this indicates that there is still considerable uncertainty associated with it. An interbenchmark workshop occurred prior to the 2019 assessment working group: the workshop revised the biomass reference points from 911587t to 1168272t for MSYBtrigger and 0.108 to 0.074 for FMSY, hence the significant drop in advice North Sea Horse Mackerel . After being benchmarked in January 2017, the CGFS and NS-IBTS survey indices were modelled with a zero-inflated model to produce a combined index. The observed trend in the last decade suggests that the stock is still at a low level in comparison with values earlier in the time-series. In 2017, the survey index showed a declining trend, and the stock remained at a low level in 2018. The result of the Length-Based Methods to estimate proxy MSY reference points for North Sea Horse Mackerel indicated that in 2018 fishing mortality was slightly above FMSY. Northeast Atlantic Boarfish . This is a small, pelagic, planktivorous, shoaling species, found at depths of 0 to 600 m. The species is widely distributed from Norway to Senegal. The directed fishery for boarfish in the NEA is a relatively new one with large catches during the early 2000s when the fishery was unregulated. Catches have reduced significantly since 2012 to the current level. Annual catch advice is provided using the data limited category 3 approach based on output from an exploratory Bayesian surplus production assessment model. The assessment model utilises catch data, an acoustic survey estimate of stock size and indices from a number of bottom-trawl surveys. The current assessment indicates that biomass peaked in 2012 at twice the historic mean before a rapid decline until 2014. Since this time the biomass level has been relatively stable. Norwegian Spring Spawning Herring . This is one of the largest herring stocks in the world. It is highly migratory and distributed throughout large parts of the NE Atlantic. This stock was benchmarked in 2016 (WKPELA). The assessment model introduced in the benchmark (XSAM), incorporates uncertainty in the input data, and has been used to provide advice after the benchmark. The SSB on 1 January 2019 is estimated by XSAM to be above Bpa (3.184 million t). The stock is declining and there is an upward revision of SSB for later years in this year’s assessment. The revision is, however, within the confidence limits of the model. Fishing mortality in 2018 is estimated to be below the management plan F that was used to give advice for 2018. A new management plan was implemented for the 2019 advisory year. Striped Red Mullet in North Sea, Bay of Biscay, Southern Celtic Seas, Atlantic Iberian Waters . This stock has been considered by WGWIDE since 2016. It is a category 5 stock without information on abundance or exploitation in relation to proxy reference points and indicators, and the evaluation is based on commercial landings. A time series of biological sampling of catches is being developed, and it may be possible to produce an analytical assessment in the near future, The advice for this stock, following the ICES precautionary approach, was given in 2017 for 2018, 2019 and 2020. Northeast-Atlantic Red Gurnard . This stock was first considered by WGWIDE in 2016, and this represents the second time the group has advised upon it. This is a category 6 stock, with large uncertainties in landings data due to poor resolution at the species level. Landings have fluctuated without trend since 2006, and discards remain significant –over 90% of catch in some cases. There remains no indication of where fishing mortality is relative to proxies and no stock indicators, and the evaluation is based on commercial landings, given the caveat that they will be incomplete. Advice for this stock is provided on the basis of the ICES precautionary approach for 2020 and 2021.