Historically, herring (Clupea harengus) has supported major fisheries in Scotland in the North Sea and on the West Coast. During the late 1970s the fisheries closed owing to dangers of complete stock collapse, but through improved recruitment and reduced exploitation these have recovered. The two main stocks contributed to Scottish landings of 25,188 tonnes worth almost £7.72 million in 2009. Pelagic trawling accounts for most of the landings.

The Scottish Pelagic Sustainability Group has recently gained Marine Stewardship Council certification of the North Sea herring fishery against their standard for environmental and sustainable fishing.

Herring is widely distributed throughout the north-east Atlantic, ranging from the Arctic Ocean in the north to the English Channel in the south. During daytime, herring shoals remain close to the sea bottom moving towards the surface at dusk and dispersing over a wide area.

Herring is unusual in having more than one spawning season. Sub-populations of North Sea herring spawn at different times and can be found spawning in almost any month although the stock is dominated by autumn spawners. Three major populations can be identified: Buchan/ Shetland herring, spawning off the Scottish and Shetland coasts during August and September; Banks or Dogger herring, spawning in the Central North Sea and off the English coast from August until October; and the Southern Bight or Downs herring, spawning in the English Channel from November until January. For most of the year the different populations mix, but during the spawning season they migrate to their separate areas. On the west of Scotland, the herring stock is composed of two groups of fish — one spawning in spring and the other in autumn. Autumn spawning takes place from late August to October around the north west of Ireland and to the west and north of the Outer Hebrides and off Cape Wrath, in depths up to 100m.

Most herring are three or four before they spawn and the number of eggs produced by an average-sized female varies between populations, but is typically of the order of 50,000. Herring are demersal spawners, depositing their sticky eggs on coarse sand, gravel, small stones and rock in an egg carpet several layers thick. Shoals of herring gather on the spawning grounds and spawn more or less simultaneously. Females release eggs in a single batch. The eggs take about three weeks to hatch depending on the sea temperature. Many autumn hatched larvae spend their first winter drifting towards nursery areas on the eastern side of the North Sea, around the Moray Firth, the Firth of Forth and in the western North Sea. Their drift rate is variable and in some years many do not reach the nursery areas. On the west of Scotland some larvae drift into sea lochs which act as nursery areas although quite a large proportion of larvae are carried through the Fair Isle channel and travel well into the North Sea. As they grow, the juvenile herring move offshore, eventually joining the adult populations. There is some evidence that as herring mature, those originating on the west coast make a return journey back to the west coast.

Herring feed mainly on crustaceans (shrimps and copepods) and young sandeels. There are no marked differences between the diets of large and small herring, only the proportions of different food items change with size.

 

Based on the most recent estimates of SSB and fishing mortality, ICES classifies the North Sea stock as being at risk of having reduced reproductive capacity and at risk of being harvested unsustainably. The SSB in autumn 2008 was estimated at 1.0 million tonnes, and is expected to remain below Bpa (1.3 million t) in 2009. Fishing mortality of adult fish in 2008 was estimated at 0.24, well above the target fishing rate of 0.14. All year classes since 2002 are estimated to be among the weakest since the late 1970s.

In the absence of precautionary reference points for west of Scotland herring the state of the stock cannot be evaluated. An analytical assessment shows that SSB (in 2009) is 1.8 times Blim. ICES considers that the stock over recent years has been fluctuating at a low level and is being exploited close to the suggested management evaluated fishing mortality rate (Fmsy = 0.25). Recruitment has been very low since 1998, and the 2001 and 2002 year classes are weak.

 

Herring in Subarea IV, Division VIId and Division IIIa are now managed under an adjusted EU-Norway management plan which was agreed upon in November 2008. This plan takes into account the recent poor recruitment.
The main elements of the plan are to maintain SSB above 800,000 tonnes (Blim); to limit TAC by ± 15% from the TAC of the preceding year; a fishing mortality of 0.25 for adult fish and 0.05 for juvenile fish if the SSB is above 1.5 million tonnes (the trigger biomass Btrig); if SSB is between Btrig and Blim then the fishing mortality will be set between 0.25 and 0.10 for adult fish, depending on SSB, and no more than 0.05 for juvenile fish; if SSB falls below Blim then a fishing mortality of no more than 0.10 for adult fish and 0.04 for juvenile fish will be set.

A reduction in fishing mortality to close to the target fishing mortality is expected to be achieved in 2009. The SSB is expected to increase slightly both in 2010 and further in 2011, indicating that the current management has the potential to reverse the decline in the stock and stabilise it above the present level. The 2008 year class is estimated to be within the range of recent low recruitments. ICES assumes that the recruitment will remain around the current low level. Delay in implementing substantial reductions in catch by not following the management plan has resulted in the SSB being at greater risk of being below Blim and lower catches.

Seven catch forecasts were presented, to show a range of options for differing overall exploitation rates, based on an interpretation of the harvest control rule or other options:

• No fishing
• Catches that are estimated to lead to SSB> Bpa in 2011
• A 15% decrease in the main North Sea fleet TAC between 2009 and 2010
• The EU-Norway management plan with 40% catch increase for herring fleets in the Skagerrak and Kattegat
• The EU-Norway management plan
• A roll-over TAC from 2009 to 2010 of 171,000 tonnes for the main North Sea fleet
• A 15% increase in the main North Sea fleet TAC between 2009 and 2010.

ICES advises that exploitation for 2010 is based on option e) above; the agreed EU–Norway management plan. Following this plan implies catches in 2010 of 164,300 t for the directed herring fisheries in the North Sea.

Council Regulation (EC) No 1300/2008 of 18 December 2008 established a multi-annual management agreement for the stock of herring distributed to the west of Scotland and the fisheries exploiting that stock. The plan is based on the following rule: 

F = 0.25 If SSB > 75,000 t	20% TAC constraint.
F = 0.20 If SSB < 75,000 t but > 62,500 t	20% constraint on TAC change.
F = 0.20 If SSB < 62,500 t but > 50,000 t	25% constraint on TAC change.
F = 0 If SSB < 50,000 t.

There is derogation from the above constraints. If the Scientific, Technical and Economic Committee for Fisheries (STECF) considers that the herring stock in the area west of Scotland is failing properly to recover, the TAC constraints may differ from those in the management agreement.

Following the agreed management plan implies catches of no more than 24,420 tonnes in 2010, which is expected to lead to an SSB of 96,000 t in 2011. The agreed management plan is consistent with the precautionary approach.

Area misreporting continues to be a problem with vessels catching fish from other areas and reporting into VIa North. This has lead to uncertainty in the amount of fish landed that is actually from stocks to the west of Scotland, although more routine use of a vessel monitoring system (VMS) has reduced this problem from past uncertainties.

The 2009 assessment shows an upward revision of the spawning stock biomass and a subsequent downward revision of F, in comparison to 2008.
The basis for the advice in 2009 has also changed from that in 2008. In 2008 the advice was for a reduction in TAC. For 2009 the advice was for an increase in catch in line with the new agreed management plan.

These figures are provisional	EU TAC	UK Share
North Sea	93,773	24,223
West coast	24,480	15,076

North Sea herring is amongst the best monitored stocks in the world with extensive commercial fishery data and independent survey data collected. Marine Scotland - Science participates in a number of surveys, particularly acoustic surveys. Recent research activities have examined stock structure in both the North Sea and on the west coast using a broad suite of techniques. These should inform future developments in sampling and have suggested possible revisions to the assessment of the west coast stock.