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 to a healthy state. The two main stocks contributed to Scottish landings of 25,326 tonnes worth almost £12.8 million in 2011. Pelagic trawling accounts for most of the landings.
The Scottish Pelagic Sustainability Group has gained Marine Stewardship Council (MSC) certification for all three commercially exploited stocks of herring (the North Sea, the Atlanto-Scandian and most recently the West of Scotland) against the MSC's 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.
The assessment for North Sea herring was benchmarked in 2012 and a new assessment methodology was used. ICES classifies the stock as being at full reproductive capacity and as being harvested sustainably, below the current management plan and FMSY targets. The year classes from 2002 to 2007 are estimated to be among the weakest since the late 1970s. The year classes 2008 and 2009 are estimated to be around the long-term average. ICES considers that the stock is currently still in a low productivity phase.
The advice, in accordance with the multiannual management plan, recommends that landings in 2012 should be 230,000 tonnes for the main North Sea fleet.
West of Scotland
ICES considers that the stock over recent years has been fluctuating at a low level. Fishing mortality has fluctuated around FMSY in recent years. The current recruitment is lower than in the historical period.
The advice is in accordance with the management plan which recommends that the TAC for 2012 should be set at 22,900 tonnes.
For the North Sea the EU-Norway management plan was reassessed by ICES in 2011, and was found to operate well in relation to the objectives of consistency with the precautionary approach and a rational exploitation pattern. However, in late 2011, a joint EU-Norway request led to an evaluation of the harvest control rule (HCR) within the management plan to determine if it is compatible with the precautionary approach if the 15% TAC constraint rule is not applied. Several options were tested, based on the assumption that the current low productivity regime for North Sea herring (observed since 2002) will continue. All options were found to be compatible. ICES concluded that the current HCR, i.e., without a 15% TAC constraint, is compatible with the precautionary approach as the risk of SSB falling below Blim is low. Although the estimates for the 2008 and 2009 year classes are above the geometric mean of the time series, and the year classes of 2007 and 2008 have been revised upwards, ICES still considers the stock to be in a low productivity phase. The management plan has proved to be an effective tool for maintaining sustainable exploitation and conserving the North Sea herring stock in this lower productivity regime.
The stock identity of herring to the west of the British Isles was reviewed by an EU-funded project. This identified Division VIa (N) as an area where catches comprise a mixture of fish from north & south Divisions of VIa and the northern VIIa. In 2008, ICES convened a study group to evaluate management for herring in these areas. In 2010, it concluded that, where single species/stock approaches give a distorted view on individual populations and catch characteristics do not reflect population dynamics, there is a need for meta-population management. It also determined that managing the VIa (N) and VIa (S) / VIIb,c ICES stocks sustainably under different mixing scenarios and misidentification levels is possible, but only with detailed information on fisheries independent data.
These data are now being collected, however it will be a number of years before ICES can provide a fully operational integrated strategy for these units. In this context the Herring Advisory Working Group recommends that the management plan for Division VIa (N) should be continued.
At the December 2011 meeting in Brussels, the Council of Ministers of the EU set the Total Allowable Catches for herring as follows:
North Sea 405,000 57,836
West of Scotland 22,900 13,438
The west coast allocation was set in line with scientific advice. A potential modification to the North Sea management plan was discussed prior to the Council, which may be considered in the future. This made provision for a less stringent catch restraint rule, and was applied to give a substantial increase to the TAC, whilst still keeping the stock within acceptable boundaries.
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.