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Microsatellite data for Atlantic Mackerel

Makrelbestanden i Nordatlanten har gennem de seneste år ændret sig dramatisk, både med hensyn til bestandskomponenterne, bestandsstørrelsen og ikke mindst makrellens udbredelse. Da makrellen desuden er en bestand med et ganske stort udbredelsesområde og med meget stor international interesse, er det vigtigt, at Danmark styrker kapaciteten og vidensgrundlaget indenfor denne bestand for at kunne yde indflydelse på de forvaltningsmæssige beslutninger. I 2020 blev der landet lidt over 1 mio. tons makrel i alt, og af dette var de danske landinger på lidt over 35.500 tons.Projektets formål har været at forbedre bestandsvurderingen og forvaltningen af makrel med fokus på makrellens Nordsøkomponent, hvor der især er en mangelfuld viden omkring udbredelse og biologi. Dette er blevet gjort ved at opbygge viden og gennemføre fire danske trawltogter (2018, 2019, 2020 og 2021) målrettet makrel i Nordsøen, som skal kombineres med de i forvejen gennemførte trawltogter fra det nordlige Atlanterhav. Resultaterne fra de danske trawltogter er blevet præsenteret hvert år til WGIPS og WGWIDE, som er de ICES-arbejdsgrupper, der har ansvar for hhv. makreltogterne og bestandsvurderingen af makrel. Som en del af projektet er der gennemført forsøg med at udvikle en multibeamsonar, der kan registrere de makrel, der søger under det pelagiske trawl under trækket. Projektet har også forsøgt at forbedre de kommercielle biologiske indsamlinger ved at udvælge den del af flåden, der går målrettet efter de pelagiske bestande, for at få en målrettet indsamling på de danske fartøjer, der står for hovedparten af landingerne. Dette er især vigtigt, fordi en meget stor andel af det danske makrelfiskeri landes i udlandet. Som et supplement til de prøver, som fiskerne selv skal indsamle, har vi gennem NordMak-projektet fået et samarbejde op at køre med Skawinspection, som har givet mulighed for at benytte alternative data, som indsamles regelmæssigt af industrien. Her har vi undersøgt om information fra disse data vil give en forbedret bestandsvurdering. Desuden har vi i projektet undersøgt makrels fødegrundlag gennem maveprøver indsamlet på makreltogterne for at få en større viden om, hvilke typer af byttedyr makrellen går efter inde i Nordsøen. Her var det især sildefisk (hovedsageligt sild og brisling), som bidrog mest til total byttevægt blandt byttefiskgrupperne, efterfulgt af andre fisk som tobis og torskefisk. Der blev fundet et tydeligt geografisk mønster.

The main objective of the survey was acoustic assessment of the capelin stock in the Iceland, East Greenland and Jan Mayen area, measuring mature and immature stock components at age 1 and older. The survey was conducted on a r/v Tarajoq on 27 August– 20 September and r/v Árni Friðriksson on 5–26 September on behalf of GINR and MFRI, respectively. The stock estimate was based on combined acoustic and trawl data from both vessels. Figure 1.1 shows the survey tracks and stations taken by the vessels.

WGWIDE reports on the status and considerations for management of the 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.2023 catch advice was drafted for mackerel, Western horse mackerel, blue whiting and herring. For the remainder, multi-annual catch advice was previously published. Benchmark assessments are proposed for 2024 for mackerel, both horse mackerel stocks, herring and striped red mullet with boarfish is scheduled to be benchmarked in 2023. Prior to any benchmark assessment for mackerel, WGWIDE recommends that a workshop to review the latest knowledge with regard to the stock component structure takes place.Northeast Atlantic Mackerel. This migratory stock is widely distributed throughout the Northeast Atlantic with significant fisheries in several ICES subareas. The assessment conducted in 2022 is an update assessment, based on the configuration agreed during the 2019 interbenchmark and incorporates updates to the commercial catch, tagging, swept area and egg survey (preliminary) data series. No recruitment index is available for the 2021 year-class as survey coverage was inadequate. Advice is given based on stock reference points which were updated during a management strategy evaluation carried out in 2020. Following a decline since 2014, SSB has been stable (above MSY Btrigger) since 2019. Fishing mortality has been increasing since 2016 and is above FMSY since 2020.Blue Whiting. This pelagic gadoid is widely distributed in the eastern part of the North Atlantic. The current assessment configuration (inter-benchmark in 2016) uses preliminary catch and sampling data along with the acoustic survey data from the current year. The 2022 update assessment indicates that SSB is increasing following strong recent recruitment and is well above MSY Btrigger. Fishing mortality has been above FMSY since 2014 but is falling.Norwegian Spring Spawning Herring. This stock is migratory, spawning along the Norwegian coast and feeding throughout much of the Norwegian Sea. The 2022 update assessment is based on an implementation of the XSAM assessment model introduced following a benchmark in 2016 and is consistent with the 2021 assessment. Following a period of decline since 2009, SSB has been relatively stable just above MSY Btrigger in recent years, due to the strong 2016 year-class. However, recruitment since 2016 is estimated to be below average and the stock size is forecast to fall below MSY Btrigger in 2024.Western Horse Mackerel. The western stock of horse mackerel is distributed throughout ICES subareas 4,6,7,8 and 9. Following a benchmark in 2017, the stock is assessed using the Stock Synthesis integrated assessment model. Stock reference points were revised in 2019. Following a period of declining SSB, there has been a modest rise since 2017, albeit from a low level. The 2022 assessment indicates that SSB is below Blim and will remain so in 2024, even under the scenario of zero catch in 2023. Based on the MSY approach, advice for 2024 is therefore for zero catch. The assessment continues to display significant retrospective issues which should be investigated by a benchmark assessment.North Sea Horse Mackerel. Catch advice for this stock is issued biennially on the basis of an assessment based on a combined index from groundfish surveys in the North Sea and the Channel. No survey index was available in 2020 due to restricted survey coverage, and the 2021 value is a reduction on the 2019 value for the exploitable stock. A length based indicator continues to indicate that fishing mortality remains above FMSY.Northeast Atlantic Boarfish. Boarfish is a small, pelagic, planktivorous, shoaling species, found over much of the Northeast Atlantic shelf but primarily in ICES subareas 4,6,7 and 8. The directed fishery occurs primarily in the Celtic Sea and developed during the early 2000s, initially unregulated before the introduction of a TAC in 2011. The stock is assessed using an exploratory Bayesian surplus production model with catch and survey data from groundfish surveys and an acoustic survey. The current assessment indicates that, following a sharp decline after 2012, biomass has been increasing in recent years. The most recent acoustic surveys indicate a period of above average recruitment from 2018-2020.Northeast-Atlantic Red Gurnard. This stock was first considered by WGWIDE in 2016 with advice issued biennially. The assessment was benchmarked in 2021 and a survey-based relative biomass indicator was developed. The 2022 update assessment continues to show the indicator fluctuating without trend since 2010. However, large uncertainties remain with regard to landings data due to poor resolution at the species level and reported discarding levels vary widely.Striped Red Mullet in Bay of Biscay, Southern Celtic Seas, Atlantic Iberian Waters. No assessment is available for this stock and information on abundance and exploitation level is limited with advice given triennially on the basis of the precautionary approach. However, there are a number of research projects underway which will inform a future benchmark and potential upgrade of the assessment category.

As a consequence of the impact of the COVID pandemic on international travel which prevented the traditional meeting from taking place, the Working Group on Widely Distributed Stocks (WGWIDE) met online via WebEx hosted by ICES. Prior to the 2020 meeting, the generic ToRs for species and regional working groups were re-prioritised by ACOM to allow the WG to focus primarily on those ToRs most applicable to the provision of advice. 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 springspawning 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 stock is highly migratory and widely distributed throughout the Northeast Atlantic with significant fisheries is most ICES subareas. A diverse range of fleets from smaller artisanal, handline vessels to large (100m+) factory freezer vessels and modern RSW trawlers and purse seiners take part in what is one of the most valuable European fisheries. The assessment conducted in 2020 is an update assessment, based on the configuration agreed during the most recent inter-benchmark exercise in 2019 and incorporates the most recent data available from sampling of the commercial catch in 2019, the final 2019 egg survey SSB estimate, an updated recruitment index and tagging time series along with 2020 survey data from the IESSNS swept area survey. Advice is given based on stock reference points which were updated during a management strategy evaluation carried out in 2020. Following a strong increase from 2007 to 2014, SSB has been declining although it remains well above MSY Btrigger. Fishing mortality has been below FMSY since 2016. There have been a number of large year classes since 2001 with above average recruitment over much of the most recent decade. Blue Whiting. This pelagic gadoid is widely distributed in the eastern part of the North Atlantic. The 2020 update assessment followed the protocol from the most recent inter-benchmark in 2016 and used preliminary catch data from 2020. Due to the cancellation of the 2020 acoustic survey, this data was not available. The effect on the assessment was minimal and limited to increases in uncertainty of the terminal year estimates. The SSB continues to decrease from the most recent maximum in 2017 mainly due to below average recruitment since 2017, although it remains above MSY Btrigger. Fishing mortality has been above FMSY since 2014. Norwegian Spring Spawning Herring. This is one of the largest herring stocks in the world. It is highly migratory, spawning along the Norwegian coast and feeding throughout much of the Norwegian Sea. The 2020 assessment is based on an implementation of the XSAM assessment model introduced at the benchmark in 2016. This years’ assessment indicates that the stock is continuing to decline from the peak in 2008 of 7Mt to just above MSY Btrigger due to successive years of average or below average recruitment. Catch advice for 2021 is given on the basis of the agreed management plan and represents a substantial increase over the 2020 advice due to an upward revision in the estimate of the 2016 year-class which is considered to be the most significant year-class since 2004.

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 adviceNorth 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.

(c) 2012 Jansen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited., peer-reviewed, It has been suggested that observed spatial variation in mackerel fisheries, extending over several hundreds of kilometers, is reflective of climate-driven changes in mackerel migration patterns. Previous studies have been unable to clearly demonstrate this link. In this paper we demonstrate correlation between temperature and mackerel migration/distribution as proxied by mackerel catch data from both scientific bottom trawl surveys and commercial fisheries. We show that mackerel aggregate and migrate distances of up to 500 km along the continental shelf edge from mid-November to early March. The path of this migration coincides with the location of the relatively warm shelf edge current and, as a consequence of this affinity, mackerel are guided towards the main spawning area in the south. Using a simulated time series of temperature of the shelf edge current we show that variations in the timing of the migration are significantly correlated to temperature fluctuations within the current. The proposed proxies for mackerel distribution were found to be significantly correlated. However, the correlations were weak and only significant during periods without substantial legislative or technical developments. Substantial caution should therefore be exercised when using such data as proxies for mackerel distribution. Our results include a new temperature record for the shelf edge current obtained by embedding the available hydrographic observations within a statistical model needed to understand the migration through large parts of the life of adult mackerel and for the management of this major international fishery., The research was funded by EURO-BASIN of the European Union’s 7th Framework Program (Grant Agreement #264933). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.