The southern component spawns in Spanish and Portuguese waters, and the western component spawns in the Bay of Biscay and northwards around Ireland and west/northwest of the UK. The third component spawns in the North Sea and Skagerrak.
The spawning stock biomass (SSB) has increased by 40% since 2002. The mackerel stock is at present harvested at increased risk. The stock has been showing much more variable recruitment over the recent years compared to the past. The 2002 year class is the strongest in history, while the 2003 year class is rather poor. The 2004 and 2005 year classes are above average. The 2006yearclass seems to be strong due to an exceptional large distribution area as one year old, but we have to wait for a clearer signal. Norway, EU and the Faroe Islands as coastal states agreed in 1999 that the total catch for 2000 and subsequent years should be in the range from 14 to18% of the stock, unless scientific advice requires modification of this catch level. Scientific analyses in 2008 provided new estimates of several reference points for mackerel, including an increased precautionary approach fishing mortality (Fpa) from 0.17 to 0.23. A new management plan has also been adopted by the coastal states.
After spawning is finished in the southern and western areas in July, the mackerel migrate northwards into the Norwegian Sea and the North Sea to feed. Here they mix with the North Sea component. The North Sea mackerel migrate within the North Sea/Skagerrak and the southern Norwegian Sea during the whole year. The western and southern components start migrating back to their respective spawning areas in December or January-February the following year.
Mackerel is a typical zooplankton feeder on the abundant species Calanus finmarchicus, but also feed on molluscs (Limacina retroversa) and small fish that can be swallowed, mainly sandeel, herring and sprat.
Main fishing nations
The main fishing nations are UK, Norway, Ireland, Russia and the Netherlands. Norway and to some extent Scotland take most of the catches by purse seiners while the other nations mainly apply pelagic trawl. The Norwegian fishery is predominantly carried out in September-November, and the main parts of the catches are taken in the northern part of the North Sea.
The stock has been measured since 1972. During this period the catches have been assumed to fluctuate between 360 000 and 840 000 tonnes. The main catches are taken in the North Sea (about 50%), The Norwegian Sea (about 10%), west of UK and Ireland (15-20%), south of Ireland and in the Channel (about 15%) and the rest in the southern area.
Regulations
The fishery is regulated according to agreements between the Faroe Islands, EU and Norway. National quotas are set for the different fishing fleets, by areas, by minimum landing size and by season.
Stock status and setting of quotas
The spawning stock biomass in relation to precautionary limits is presently at increased risk. There are considerable uncertainties in the catch levels, including unaccounted mortality due to slippage and discards. Catch statistics are an important input parameter in the stock assessment. Repeated analyses demonstrate that the unaccounted mortality is probably still at least 60% higher than those officially reported.