Marine Institute

Mackerel and Horse Mackerel Egg & Larval Surveys

Fish egg and larval surveys are carried out to map spawning grounds and to derive information on the adult spawning stock.  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

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. 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).

2013 Mackerel Egg Surveys

In 2013, ten research institutes from nine countries - Scotland, Norway, Germany, the Netherlands, Spain, Portugal, Ireland, Iceland and the Faeroes - took 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, were carried out. The first survey started on February 9th off the coast of Portugal, and the Marine Institute finished the programme on July 31st to the west of Scotland. Download the survey reports for the Marine Institute's February and July surveys.


Map of 2013 mackerel egg survey coverage

2013 mackerel egg survey coverage

Provisional results from recent surveys

Preliminary egg and fecundity numbers from all the surveys combined were compiled by the survey coordinator and these provisional results were presented to WGWIDE, the Working Group on Widely Distributed Stocks, in August 2013. This Working Group carries out the stock assessments for mackerel and horse mackerel. The provisional data indicated that there was a 31% increase in total annual NEA mackerel egg production in 2013 compared to 2010. Horse mackerel egg numbers decreased by almost 64% in the same time period.
Finalised egg and fecundity results were produced for WGMEGS for its annual meeting in April 2014. The result from the analysis of the complete datasets was the same as that provided to WGWIDE in August.
Historically peak spawning of mackerel would take place between April and June. In 2010 peak spawning was found to have taken place much earlier in the year, in the Celtic sea and west of Ireland. In 2013, in an effort to sample this early spawning, surveying in the Celtic sea and Bay of Biscay was carried out earlier than previously. Unfortunately once again peak spawning appears to have taken place prior to this earlier start and has probably been missed. This increasingly early spawning will need to be addressed when planning for the 2016 surveys takes place.
Horse mackerel eggs were found early in the year in the Bay of Biscay and the Cantabrian Sea. They moved up the shelf edge and onto the Porcupine bank in April, and continued moving north up to the end of July. Egg numbers were low throughout all the 2013 surveys however, with the greatest numbers being recorded in May, June and July.