Marine Institute

Mackerel and Horse Mackerel Egg & Larval Surveys

The international mackerel and horse mackerel egg surveys take place between February and the end of July every 3 years. The next surveys are due to carried out in 2019.  Fisheries Ecosystems Advisory Services (FEAS) are part of a consortium of eight European countries that run the international mackerel and horse mackerel egg surveys.

 Gulf sampler

Gulf Sampler, used to collect fish eggs

Purpose of the survey

The aim of the international mackerel and horse mackerel egg survey program is to estimate the spawning stock biomass (the total weight of all sexually mature fish in the population) of the North-east Atlantic mackerel and horse mackerel stocks. This data feeds into stock assessments as fisheries independent information. In addition, the data provides important information on the timing and location of spawning for mackerel and horse mackerel. The survey has been carried out every three years since its inception in 1977 and can therefore provide important information about the distribution and timing of spawning in relation to climate change.

How is the survey carried out

The international mackerel and horse mackerel egg surveys take place every 3 years and cover the spawning grounds for both species in the NE Atlantic. Currently the survey area extends from southern Portugal to the Faroes, and takes place between February and the end of July. A plankton sampler called a GULF VII is deployed from a survey vessel on a V-shaped tow. The tows take place to a maximum depth of 200m. The GULFs use a net with a mesh size of 250µ. Scientists extract, identify, count and stage the number of fish eggs from these plankton samples, and relate these to the number of eggs produced per female fish to obtain an estimate of the size of the spawning stock.

To find out more about: Where fish eggs are found? How species are identified? etc.. please download 'Fish Egg & Larval Surveys' (1.1 Mb pdf).

2016 Mackerel Egg Surveys

The most recent egg survey was carried out in 2016. Nine research institutes from eight countries, Scotland, Germany, the Netherlands, Spain, Portugal, Ireland, Iceland and the Faroes, participated, (see map). The survey was divided into six sampling periods, from February to July. Nineteen surveys, totaling 367 days of ship time, were carried out. Ireland started the first survey on February 4th to the west of Ireland, and Scotland finished the programme on July 21st to the west of Scotland. Download the survey reports for the Marine Institute's February and July surveys.

Historically peak spawning of mackerel would take place between April and June in the Celtic sea and west of Ireland. In 2010 and 2013 peak spawning was found to have taken place much earlier in the year, February / March, and was concentrated in the Bay of Biscay.

In 2016, in an effort to sample this early spawning, surveying in the Bay of Biscay started earlier than previously. This year however peak mackerel egg production took place once again in May / June, but it took place in northern waters, to the west of Scotland and south of Faroes. Horse mackerel egg production was very low in 2016, it turned out to be the lowest in the time series.


Mackerel egg survey coverage
Mackerel egg survey coverage

Provisional results from recent surveys

In each survey year egg numbers and preliminary fecundity results from all the surveys are compiled by the survey coordinator. For mackerel the data are worked up to calculate a spawning stock biomass, SSB, while for horse mackerel the data are presented as total egg production. These provisional results are presented to WGWIDE, the Working Group on Widely Distributed Stocks, for its meeting each August. WGWIDE carries out the stock assessments for both mackerel and horse mackerel. Finalised fecundity results are produced for the WGMEGS meeting the year following each survey. WGMEGS then produces a final survey SSB for mackerel for use by WGWIDE.  

Survey Funding

Ireland's Mackerel Egg Survey is part of Ireland's Data Collection Scheme which is carried out under Ireland's Operational Programme (OP), co-funded by the European Maritime and Fisheries Fund (EMFF) and by the Irish Government.

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