Archive for January, 2014

Understanding North East Atlantic Mackerel

Tuesday, January 21st, 2014

The reduction in size, quantity, and late arrival of east coast mackerel off Greystones Co. Wicklow post 2010 prompted a little research. Is it the result of over quota fishing due to the entry of Iceland, the Faroe Islands, and Greenland into the fishery, a behavioural change, or the influence of a warmer climate? The following information derived from academic papers, Government and industry reports, and books on the subject provides the answer and a little more.

North East Atlantic mackerel scomber scombrus are a genetically identical species subdivided into three distinct components Western, Southern, and North Sea, each of which migrate and intermingle at various times throughout the calendar year.

All three components have different spawning grounds and spawning seasons with the result that they display different growth rates. In principal the Southern, Western, and North Sea stock elements should each be managed separately, however because of the difficulty in separating the individual stocks ICES (The International Council for the Exploration of the Seas) assess and manage the stock as one collective unit.

Mackerel migrate in winter and early spring to and from their spawning grounds, post spawning to their feeding grounds, and finally to the areas where they overwinter. These migrations can and have changed overtime based on historical information gleaned from early scientific studies and fishing reports, most likely due to changing environmental conditions.

North East Atlantic mackerel migration routes.

Mackerel that migrate into the Irish Sea in the summer months are derived from the southern component. Predominantly juvenile fish ranging in age from 1 – 3 years, their reduced numbers off Greystones, Co. Wicklow post 2010 are as a result of over fishing by the Spanish and Portuguese pre 2010.

In 2009 Spain and Portugal between them landed 107,748 tonnes of mackerel. As this combined haul was way over quota the EU in 2011 introduced a regulation scheduling payback by the Spanish fleet for over fishing in 2010 which will last until 2015. For the record, in 2012 the Spanish landed 28,789 tonnes of mackerel.

The European mackerel fishery extends from the Bay of Biscay to the Norwegian Sea, for management purposes ICES has compartmentalised the sea area into sectors or divisions. North East Atlantic Mackerel inhabit an area from division IXa off the Iberian Peninsula to division IIa off Norway, and into divisions IVa and IVb within the North Sea.

However, nature knows no boundaries and because the environmental factors which influence species such as mackerel are in constant flux, what underpins their geographical spread and migration patterns are to this day still not fully understood.

European Mackerel Fishery by Sea Area.

The stock status is currently exploited above the precautionary level, but if current fishing patterns are continued is likely to fall below Bpa in the short-term (MSC Fishery Surveillance Report, 2010).

The Fish

  1. North East Atlantic Mackerel are a pelagic species inhabiting the water column anywhere from the surface to the sea floor.
  2. Although genetically identical the North East Atlantic mackerel comprises three distinct stock components, Southern, Western, and North Sea.
  3. Lack of a swim bladder means that mackerel have to swim constantly or they will sink.
  4. Mackerel swim with their mouths open feeding by filtering plankton through their gills. The diet of mackerel also includes fish larvae and small fish.
  5. Mackerel prefer water temperatures above 6 degrees centigrade.
  6. North East Atlantic Mackerel are gradual spawners starting with the southern component off the Iberian Peninsula in January and finishing with the western component in early July north of Scotland.
  7. The North Sea mackerel component migrates south from off Norway spawning in the eastern North Sea in July.
  8. Mackerel are fully mature by year four and depending on conditions can lay eggs from certainly year three.
  9. Natural mortality is assumed to be 0.15 or 15% annually over all age groupings.
  10. A mature female of 37 cm can produce 500,000 – 700,000 eggs during a season, with a typical female releasing 250,000 eggs over 20 separate batches (Simmonds J, 2001).
  11. In certain years when spawning conditions are unfavourable, to allow future progeny every available chance of survival, mackerel will instinctively reabsorb their eggs, a condition called Atresia. Due to this fact establishing with any accuracy the fecundity of mackerel can prove well nigh impossible (Lockwood. W S, 1988).
  12. Migration patterns of juvenile and mature fish differ.
  13. North Sea mackerel mix with the Western component in the winter off Shetland.
  14. The western component migrates south west mixing and spawning alongside the southern component in mid summer.
  15. Post spawning the western component migrates northwards.
  16. The heaviest mackerel recorded was landed in Killybegs in 1990, weighing 2.66 kg it measured 60cm in length.
  17. Spring mackerel landed in the late 19th century weighed on average 1.2 kg which is much larger than today’s average.
  18. Mackerel do not possess a swim bladder thus they give off a poor acoustic signature; high frequency SONAR devices are capable of detecting them.

Mackerel behaviour and water temperature are inextricably linked with their preferred comfort zone above 6 degrees centigrade, as is the availability of plankton concentrations which in 2012 were at their lowest levels since 1996 in the northern and western parts of the north east Atlantic.

An abundance of mackerel coupled with a decrease in zoo plankton density could have the effect of spreading the population out over a very wide area to fulfill dietary needs. This is the most plausible explanation as to their movement into more northerly waters.

North East Atlantic mackerel in recent surveys have exhibited a decrease in size relative to age indicating reduced food intake which could be due to an increase in competition with their own kind and other species such as herring for available plankton.

Spawning Stock Biomass for North East Atlantic Mackerel.

Catching Methods:

  1. Freezer trawlers up to 150 meters in length work singly using mid water pelagic nets, Dutch, German, majority of English and French. Russian’s in area IIa and now the Icelandic’s.
  2. Purse seiners, greater than 20 meters in length, fitted with Refrigerated Sea Water (RSW) holding tanks, Norwegian, fish over wintering mackerel close to shore. Also a large element of the Spanish fleet which targets mackerel early in the year close to the northern Spanish coast.
  3. Pelagic trawlers ranging up to 100 meters in length operate individually and in pairs, fitted with refrigerated sea water (RSW) holding tanks, Iceland, Faroes, Scotland, and Ireland. Ireland and the Faroe Islands tend to pair trawl.
  4. Lines and Jigs, Norway and England, Skagerrak and off Cornwall. Spain also has a large hand line fleet.
  5. Gill nets, Spain and Norway.
  6. Fish weighing more than 600 grams attract a premium price – reason to high grade and or discard – certainly a problem in area IIa and sub area IV pre 1994.
  7. Discarding of juvenile mackerel has historically been a problem and was a key factor in setting up the Cornish box. Discarding is greatly influenced by quota and market price.
  8. 1st Quarter commercial fishing patterns – winter fishery off Irish West coast and Southern Bay of Biscay.
  9. 2nd Quarter commercial fishing patterns – Icelandic and Northern Waters.
  10. 3rd Quarter commercial fishing patterns – Northern and Icelandic waters plus off Shetland.
  11. 4th Quarter commercial fishing patterns – North coast of Scotland and Shetland.
  12. 70% of the present mackerel catch are within age bands 4 – 7, getting older as one moves north.
  13. Over 50% of the mackerel catch within the southern fishery is dominated by 1 – 3 year old fish.

European Mackerel Fishery General Information

  1. Exploiting countries are Norway, Scotland, Ireland, Russia, and Spain, with Denmark, Holland, Germany, and France falling in behind.
  2. Distribution of catches must not be taken to relate to distribution of stocks, this is just where the fleet gains the most economic benefit from effort.
  3. Because the fishery is aimed at human consumption illegal practices to include misreported catches, unreported catches, high grading, and discarding of under size fish can occur the result of certain fishermen maximising their return on effort by landing only marketable fish.
  4. In 1979 cumulative annual landings of North East Atlantic mackerel derived from all three stock components (Western, Southern, and North Sea) topped 840,000, a return closely repeated in the early to mid 1990’s and again in the early 2000’s.
  5. The Norwegian purse seine fishery at its peak in the late 1960’s was taking an unsustainable 900,000 tonnes of North Sea mackerel per annum. The fishery collapsed in the early seventies and has never recovered, its spawning stock biomass (SSB) reduced from above 3 million tonnes in the mid 1960′s to 100,000 ton
  6. Catch returns for Greenland appeared for the first time in 2011 and again in 2012.
  7. The Cornish box began operation in 1980 and was fully closed to all methods other than quota regulated vessels using hand lines or gill nets from 1985. Recognised as a nursery area with a juvenile population that can reach up to 80%, the Cornish box is perceived as important to western stock recruitment.

ICES suspended giving advice on the North East Atlantic mackerel fishery quota for 2014 citing flawed scientific modals pre 2012 and the availability of new information, which still has to be verified, indicating a spawning stock biomass in excess of that which had been previously thought.

Instead the organisation took a mean based on total official catches over the last three years, to include Iceland, the Faroe Islands, and Greenland, and set that as the quota. Hence upwards of 864,300 tonnes of mackerel will be removed from the North East Atlantic in 2014, the forth year in a row that close to 900,000 tonnes of mackerel have been extracted. When sustained annual fishing attrition of mackerel on this scale occurred before the North Sea mackerel fishery collapsed.


Andrews J, Nichols J (2013) PFA North East Atlantic Mackerel Fishery Surveillance Report, Moody Marine Ltd.

Fahy E, (2013) Overkill! The euphoric rush to industrialise Ireland’s sea fisheries and its unravelling sequel.

ICES WGWIDE, North East Atlantic Mackerel, Report 2013.

Jansen T, Campbell A, Kelly C, Hatun H, Payne MR (2012) Migration and Fisheries of North East Atlantic Mackerel (Scomber scombrus) in Autumn and Winter. PLoS ONE 7(12): e51541. doi:10.1371/journal.pone.0051541.

Lockwood S J, (2012) North East Atlantic Mackerel, A Review of Stock Status and Prognosis, Coastal Fisheries and Conservation Management.

Marine Conservation Society, North East Atlantic Mackerel Fishery, Position statement, February 2013.

Marine Institute, The Stock Book, 2013.

Marine Institute, The Stock Book, 2012.

Marine Institute, The Stock Book, 2011.

Molloy J, (2004) The Irish Mackerel Fishery and the Making of an Industry, Killybegs Fisherman’s Organisation Ltd and The Marine Institute.

MSC Fishery Surveillance Report, The Danish Pelagic Producers Association, North East Atlantic Mackerel Fishery, Report N. 2010-0007 Revision 00 – Date 19.07.2010, PP 1 – 16.

Simmonds, E. J., Portilla, E., Skagen, D., Beare, D., and Reid, D. G. 2010. Investigating agreement between different data sources using Bayesian state-space models: an application to estimating NE Atlantic mackerel catch and stock abundance. – ICES Journal of Marine Science, 67: 1138–1153.

Simmonds J (2001) North Eastern Atlantic Mackerel Stocks, Pelagic News.

See also: Where are our mackerel?

See also: ICES decision to increase the 2014 North East Atlantic mackerel quota is based on expedience rather than science.