Fish egg and larval surveys are carried out to map spawning grounds and to derive information on the adult spawning stock. In order to estimate the number of adult fish in the stock, plankton surveys are conducted, which estimate the number of eggs spawned during the entire spawning season. Fisheries Ecosystems Advisory Services (FEAS) are part of an international consortium of nine European countries that run the international mackerel and horse mackerel egg surveys every three years.
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 running since 1977 and therefore provides 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 in the NE Atlantic from Portugal to the north of Scotland between February and the end of July. A plankton sampler called a GULF VII is deployed from the ship on a V-shaped tow which filters seawater between the surface and 200m water depths. The GULFs use a net with a mesh size of 250µ. Mackerel and horse mackerel eggs are identified by size and their state of development. 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).
Mackerel Egg Surveys
Ten research institutes from nine countries - Scotland, Norway, Germany, the Netherlands, Spain, Portugal, Ireland, Iceland and the Faeroes - take part in the programme to cover the spawning area, see map, between southern Portugal and Iceland. The survey is divided into six sampling periods, from February to July. Seventeen surveys, totalling 345 days of ship time, are carried out. The first survey starts in February off the coast of Portugal, and the Marine Institute finishes the programme in the end of July to the west of Scotland.
Mackerel egg survey coverage
Analysis of survey results
Preliminary egg and fecundity numbers from all the surveys combined are compiled by the survey coordinator and these provisional results are presented to WGWIDE, the Working Group on Widely Distributed Stocks. This Working Group carries out the stock assessments for mackerel and horse mackerel.
Finalised egg and fecundity results are produced for WGMEGS for its annual meeting in April.
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.