Information

Fish and Shellfish Stocks: 2013

Information on the state of fish and shellfish stocks of commercial importance to the Scottish fleet, inclduing Total Allowable Catches (TACs) for each stock.


Northeast Atlantic Mackerel Stocks

Mackerel ( Scomber scombrus) is the most important pelagic species for the Scottish fishing industry. It is caught predominantly with pelagic trawl mainly in western waters and the North Sea.

2013 position : UK share 160,118 tonnes
Last Year : 152,368 tonnes
Landed into
Scotland in 2011 : 85,516 tonnes
Value for 2011 : £101 million

Biology
The mackerel ( Scomber scombrus) caught by the Scottish pelagic fleet belong to two different stocks - the North Sea and the western. This separation is based on differences in the timing and the areas used for spawning. North Sea mackerel overwinter in the deep water to the east and north of Shetland and on the edge of the Norwegian Deep. In the springtime, they migrate south to spawn in the central part of the North Sea from May until July. 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. Over the past twenty years, the pattern of their southerly migration has changed dramatically in both timing and route. In the 1970s and 1980s this movement occurred in late summer and autumn with the fish passing through the relatively shallow waters of the Minch. Now the migration occurs gradually 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 in the north of the area and to the west of the shelf edge.

By the time they reach three years old, most mackerel are mature. At one year old, only a small proportion of females are mature and able to spawn, while more than half can spawn at two years old. 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. By weight, almost half of the food consists of crustacea (shrimps). The remainder is made up of juvenile fish such as sandeel, herring and Norway pout.

Left: Spawning Grounds. Right: 2010 Distribution of Landings by Scottish Vessels (Tonnes).

ICES Advice on Management

Information Source: ICES advice 2012 ( http://www.ices.dk/sites/pub/Publication%20Reports/Advice/2012/2012/mac-nea.pdf). Quoted text in italics.

Landings, Recruitment (age 0), Fish mortality and Spawning Stock Biomass

MSY and precautionary approach reference points

Type Value
Management plan SSB trigger 2.2 million t
F target 0.20-0.22
MSY Approach MSY B trigger 2.2 million t
F MSY 0.22
Precautionary Approach B lim 1.67 million t
B pa 2.3 million t
F lim 0.42
F pa 0.23

State of stock and advice

  • Fishing mortality in 2011 is estimated to be 0.31, above F MSY and F pa. This means that approximately 27% by number of all fish between 4 and 8 years of age were caught.
  • Spawning stock biomass has increased considerably since 2002 and remains high, above B pa and MSY B trigger, but is currently declining. The 2005 and 2006 year classes are the strongest year classes in the time-series. There is insufficient information to reliably estimate the size of the 2009-2011 year classes.
  • SSB in 2012 is estimated to be well above B pa and MSY B trigger at around 2.7 million tonnes.
  • Fishing mortality and biomass are both above the precautionary limits and the level of F which is consistent with achieving maximum sustainable yield (F 2011> F MSY).
  • The advice is in accordance with the Norway, Faroe Islands and EU management plan which recommends that catches in 2013 should be between 497,000 tonnes and 542,000 for NEA mackerel.

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 0.36 for 2012 is well above F MSY and the stipulated range in the management plan for this stock. Maintaining catches at this level of fishing mortality in 2013 and 2014 would result in a decrease of the stock size in the short term.

Management outcomes for 2013

At the December 2012 meeting in Brussels, the Council of Ministers decided that the 2012 EU Total Allowable Catch for northeast Atlantic mackerel should be 296,538 tonnes. The UK quota was provisionally set at 160,118 tonnes.

Management of this stock continues to be complicated by unilateral action taken by Iceland and Faroes and a failure to reach political solution.

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