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Mackerel (Scomber scombrus) is the most valuable fish species to the whole of the Scottish Fishing industry. Worth in 2011, over £89 million; the main western waters stock contributes most mackerel to the 89,142 tonnes landed in 2011. Pelagic trawling is the main fishing method – small quantities are taken by hand-lining.
In January 2009 the Scottish Pelagic Sustainability Group gained Marine Stewardship Council (MSC) certification of the North East Atlantic mackerel fishery against the MSC's standard for environmental and sustainable fishing.
The mackerel (Scomber scombrus)caught by the Scottish pelagic fleet belong to two different stocks — the North Sea and the Western Stock. North Sea mackerel over-winter in the deep water, to the east and north of Shetland and on the edge of the Norwegian Deep. During spring they migrate south to spawn in the central part of the North Sea. The western mackerel stock is found near to the continental slope, over a vast area. These fish spawn between March and July, mainly to the south and west of the UK and Ireland. When spawning is finished, most of the spent fish move to the feeding grounds in the Norwegian Sea and the northern North Sea where they mix with the North Sea stock.
Some western stock mackerel, predominantly small individuals, also enter the North Sea through the English Channel. The western stock mackerel travel long distances between the feeding grounds and the spawning areas. In the 1970s and 1980s this movement occurred in late summer and autumn with the fish passing through the Minch. Now the migration occurs later in the year and is further offshore. The pattern of the return northerly journey, after spawning, has remained relatively constant. The boundaries of the spawning areas have also slowly changed, with an increase in spawning activity to the north and west of the area.
By the time they reach three years old, most mackerel are mature and at two about half can spawn. Female mackerel shed their eggs in about twenty separate batches over the course of a spawning season. An average-sized fish produces around 250,000 eggs. Juvenile mackerel grow quickly and can reach 22cm after one year and 30cm after two years. The diet of mackerel can vary with the area and the season and consists of crustacean (shrimps) and juvenile fish such as sandeel, herring and Norway pout.
Fishing mortality in 2011 is estimated to be 0.31, above FMSY and Fpa. Fishing mortality was above Flim during the early 2000s. SSB has increased considerably since 2002 and remains high, above Bpa and MSY Btrigger, but is currently declining. The 2005 and 2006 year classes are the strongest year classes in the time-series.
The advice is in accordance with the Norway, Faroe Islands and EU management plan which recommends that catches in 2012 should be between 586,000 tonnes and 639,000 for NEA mackerel.
Effective management of this stock continues to be compromised by unilateral action taken by Iceland and Faroes, and a failure to reach a political solution.
The TAC should apply to all areas where mackerel is caught. Catches since 2008 have been considerably in excess of ICES advice which was based on the management plan. This situation continued in 2011. The absence of comprehensive international agreements on the exploitation of the stock remains a critical concern, and prevents control of the total exploitation rate. A projected fishing mortality of 0.31 for 2011 is above that stipulated in the management plan. If the level of catch associated with this fishing mortality were to be maintained in 2012 and onwards, then the spawning stock biomass is expected to decline rapidly to below Bpa within a few years.
In June 2009, an agreement was concluded between contracting parties to the Coastal States on mackerel banning high-grading, discarding, and slipping from pelagic fisheries targeting mackerel, horse mackerel, and herring beginning in January 2010.
At the December 2011 meeting in Brussels, the Council of Ministers of the EU set the Total Allowable Catches for northeast Atlantic mackerel at 278,948 tonnes. The UK quota was provisionally set at 152,368 tonnes.
Marine Scotland - Science (MSS) plays a major role in the planning, coordination and analysis of the triennial international egg survey, which is used to tune the stock assessment. During the 2007 survey, additional trips were conducted by MSS (then FRS). The next egg survey takes place in 2013.
MSS scientists were involved in the development of a revised management plan for mackerel, agreed by Coastal States in 2008 and in use since 1st January 2009. Under the plan, the TAC is set within a clearly defined range, dependent on the estimated fishing mortality.
MSS is also involved in applied fisheries acoustics research, in which the identity of mackerel schools from multi frequency acoustic data are being looked at.