Mackerel (Scomber scombrus) is the most valuable pelagic fish species for Scottish Fishermen worth £79.74 million. The main western waters stock contributes most mackerel to the 94,550 tonnes landed in 2009. The much smaller North Sea stock remains far below recommended levels and the advice is to protect it. Pelagic trawling is the main fishing method – small quantities are taken by hand-lining.

The Scottish Pelagic Sustainability Group recently gained Marine Stewardship Council certification of the North East Atlantic mackerel fishery against their 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.

 

Based on the most recent estimate of spawning stock biomass (in 2009), ICES classifies this stock as having full reproductive capacity. Based on the most recent estimates of fishing mortality (in 2008), ICES classifies the stock as being harvested at increased risk.
Fishing mortality in 2008 is estimated to be just above Fpa. SSB has increased by 47% since 2002 and is currently estimated to be above Bpa. The 2002 year class is the highest on record. Subsequent year classes are estimated to be about average. There is insufficient information to confirm the sizes of the 2007 and 2008 year-classes.

 

 

In October 2008 a management plan for mackerel in the Northeast Atlantic was agreed upon by Norway, the Faroe Islands and the EU. The plan would restrict fishing for mackerel on the basis of a TAC consistent with a fishing mortality in the range of 0.20 - 0.22 with restriction on change in TAC of less than 20% per year, provided the spawning stock biomass remains above 2.2 million tonnes. If SSB falls below 2.2 million tonnes a TAC is fixed according to expected landings when fishing the stock at a fishing mortality rate determined by the following:

In the event that SSB falls below Blim a TAC may be decided upon by a fishing mortality rate that will be less than one determined by the above formula.
ICES concluded that the management plan is precautionary, assuming that the TAC equals the total removals from the stock.
For 2010 ICES advises a 5 – 13% decrease in TAC. This is in line with fishing mortality rates set out in the management plan (F between 0.20 and 0.22) and implies catches between 527,000 and 572,000 tonnes. The SSB is expected to remain stable in 2011 for a catch in this range.

Catches in 2007 and 2008 have been considerably in excess of the ICES' advice. The absence of effective international agreements on the exploitation of the stock (between all nations involved in the fishery) is a cause of concern and prevents control of the exploitation rate of the stock. According to the short-term forecast, the total estimated catch in 2009 results in an estimated fishing mortality of 0.31, which is above that stipulated in the management plan (it should be noted that this F would be lower without the significant additional catches in excess of the TAC). The 2010 TAC advice given above should apply to all areas fished.
Mackerel is mainly exploited in a directed fishery for human consumption. This fishery tends to target bigger fish and there is evidence that this causes discarding of smaller, less marketable fish.

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.

These figures are provisional	EU TAC	UK Share
North Sea mackerel	22,382	1,395
West of Scotland mackerel	295,366	172,268

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 2010.

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.