ICES Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS: outputs from 2020 meeting)

The ICES Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS) coordinates the mackerel and horse mackerel egg survey in the Northeast Atlantic (NEA) and the mackerel egg survey in the North Sea. The working group plans and reports on these surveys, with recent attention focused on the execution of the surveys given the increasing demands related to covering the expanding survey area as well as balanced fecundity sampling. WGMEGS also addresses data quality assurance in macke-rel fecundity and total annual egg production estimation.Currently, there are 3 surveys in place which are carried out triennially and deliver standing stock bio-mass (SSB) indices: (1) the survey for the western and southern stock components of the NEA mackerel stock, as well as for the western horse mackerel stock, (2) the survey for the NEA mackerel North Sea stock component, and (3) the survey for the southern horse mackerel stock.For the North Sea component, the egg survey in 2017 revealed an estimated egg production of 201*1012, resulting in an SSB of 287*103 tons. This is a strong increase of more than 100*103 tons com-pared to 2015 (SSB = 170*103 tons). While peak spawning in the North Sea was covered, the coverage of the complete spawning season and area was insufficient to produce a reliable estimate of survey in-dices.In 2019, the application of an alternate transect survey design made it possible to survey the persis-tently expanding mackerel spawning area and season. Northern and northwestern spawning bounda-ries for mackerel during survey periods 5 (weeks 19 – 22) and 6 (weeks 23 – 26) were not fully deline-ated. Peak spawning was observed in period 4 (weeks 16 – 18). Subsequent analyses of survey results in conjunction with results from exploratory surveys in the inter-survey-years showed that the mackerel core spawning area was covered and a reliable estimate of mackerel annual egg production was deliv-ered. The estimate of total mackerel egg production was 1.64*1015, which is a decrease of 7.6% com-pared to that of 2016 (rev. 1.77*1015).Realized fecundity was estimated at 1147 per g female, revealing the SSB for the NEA mackerel stock in 2019 at 3.09 million tons indicating at 12 % decrease since the 2016 survey (SSB = 3.52 million tons). At only 1.78*1014 , total annual egg production (TAEP) in western horse mackerel was found to be lowest production reported in the time series since 1992. The spawning maximum was detected in the last pe-riod 7 (weeks 27 – 29). It can, thus, not be concluded that peak spawning and the entire temporal ex-tent of horse mackerel spawning had been sufficiently covered.To further improve the quality of the index time series, WGMEGS will continue to dedicate much of its work to survey design and quality assurance in mackerel egg production and fecundity estimation.