Fish egg and larval surveys are carried out to map spawning grounds and to derive information on the adult spawning stock. Fisheries Science Services are part of an international consortium of eight European countries that run the international mackerel and horse mackerel egg surveys every three years.
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 will feed into the stock assessment 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 to collect plankton through a net of fine mesh size. Scientists count the number of recently spawned fish eggs and relate these to the eggs produced per female fish to obtain an estimate on 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).
2010 mackerel egg surveys
In 2010, ten research institutes from nine countries, Scotland, Norway, Germany, the Netherlands, Spain, Portugal, Ireland, and for the first time Iceland and the Faeroes, took part in the programme to cover the spawning area between Portugal and the west of Scotland during six spawning periods from January to July. Overall, sixteen surveys, totalling 334 days of ship time, were carried out. The surveys started in early February off the coast of Portugal, and the Marine Institute finished the programme at the end of July off the northwest of Ireland. Download the survey reports from the Marine Institute's March and July Surveys, March 2010 Mackerel Egg Survey (PDF, 794 KB) and July 2010 Mackerel Egg Survey (PDF, 1 MB)
2010 International Mackerel & Horse Mackerel Egg Survey - Area Covered
Provisional results from recent mackerel egg surveys
Provisional egg numbers were presented to WGWIDE, the ICES Working Group which carries out the stock assessments for mackerel and horse mackerel stocks, for their assessment meeting at the end of August. These figures indicated that there was a 23% increase in total annual NEA mackerel egg production in 2010 compared to 2007. This is the highest annual production since back to 1998.
Horse mackerel eggs were found early in the year in the Bay of Biscay and the Cantabrian Sea. They started moving up the shelf edge and onto the Porcupine bank in April. There was a large drop in numbers of horse mackerel eggs found in May but numbers increased again in the shelf edge and the Porcupine bank in June and July. 2010 egg production showed a 30% decrease on 2007 numbers. However the figure for 2007 was a 60% increase on 2004 numbers and 78% on 2001.
Finalised egg results and fecundity analysis will be produced by WGMEGS, the ICES working group for the international mackerel and horse mackerel egg surveys, which will meet in April 2011. This working group will calculate total seasonal Stage 1 egg production estimates for mackerel and horse mackerel, and use finalised fecundity data to provide SSB estimates for mackerel. It will also look at the effectiveness of the 2010 survey in relation to previous surveys.