Historically, herring (Clupea harengus) has supported major fisheries in Scotland in the North Sea and on the West Coast. During the 1970s the fishery closed owing to dangers of complete stock collapse, but through improved recruitment and reduced exploitation these have recovered. The two main stocks contribute Scottish landings of 57,081 tonnes worth £13.2 million. Pelagic trawling accounts for most of the landings.

Biology

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. SSB in 2006 was estimated at 1.2 million tonnes, and is expected to remain below Bpa (1.3 million t) in 2007. All year classes since 2001 are estimated to be among the weakest since the late 1970s. The cause of reduced recruitment is not known but is thought not to be the result of fishing.

Based on the most recent estimates of SSB and fishing mortality, ICES considers that the West of Scotland stock is currently fluctuating at a low level and is being exploited slightly above Fmsy. The 2001 and 2002 year classes are very weak.

North Sea Herring

West Coast Herring

Management

In the North Sea there is a joint management agreement between the EU and Norway. Implementing the management plan implies a reduced fishing mortality (F). Corresponding TACs and allocations among fleets are indicated in ICES catch options tables. Changes in TAC between years would be limited to 15% unless paragraph 6 of the management plan is invoked. Due to the current circumstances of a sequence of five poor recruiting year classes of North Sea herring, ICES advises that it is particularly important that the decline of future spawning stock biomass is addressed with sufficient action to ensure the safety of the spawning stock in the next few years. Accordingly, ICES recommends that paragraph 6 should be invoked. This would result in a catch of 175,000 tonnes in The North Sea.

There are no explicit management objectives for the VIa north herring stock. However, a proposed management plan has been developed. This management plan was evaluated by ICES in 2005 and found to be consistent with the precautionary approach. Fishing according to the proposed management plan would imply catches up to 15,000 tonnes. The proposal was evaluated and found to be consistent with the precautionary approach. In the absence of precautionary approach boundaries ICES recommends following the plan.

Scientific developments in Scotland

North Sea herring is amongst the best monitored stocks in the world with extensive commercial fishery data and independent survey data collected. FRS participates in a number of surveys, particularly acoustic surveys. Some new proposals for improved monitoring of the West coast stock have also been put forward for 2008. Recent research activities have examined stock structure in both the North Sea and on the west coast using morphological and genetic techniques. These should inform future developments in sampling and possibly management arrangements on the West coast.