Use of data from the commercial fishing industry in the management of Norwegian spring spawning herring (Clupea harengus L.).

Every year the commercial fish industry of Norwegian spring spawning herring collects a severe amount of data for sales purposes that in fact could be very useful for scientific and management purposes too. The present ‘paper describes a new method for estimation of catch at age, which takes advantage of information of catch by size groups collected by The Norwegian fishemen’s sales organisation for pelagic fish. At landing herring catches for human consumption are divided into 5 size groups by individual weights as follows: group 1 (>333 g), group 2 (200-333 g), group 3 (125-200 g), group 4 (83-125 g) and group 5 (~83 g). Annually many thousands of catches and hundred thousands of tonnes are sampled in this way. In the new method these data on size group composition are combined with biological samples with age readings in a similar way as with the traditional method using age at length keys. Comparisons between the new and the traditional sampling of the fishery suggest that the new method is more reliable, mostly due to the enormous amounts of size group samples used in the calculations. The ICES Northern Pelagic and Blue Whiting Fisheries Working Group has accepted the new method. There are also other useful commercial data on Norwegian spring spawning herring. One example is data on proximate composition (fat and water content) analysed at meal and oil factories and local processing plants, which could be used to analyse seasonal and annual variations in energy loss. Another example is data on individual weights and gonad weights, which could be used to assess the maturation process and reproductive investment using indexes like GSI. The mentioned data on size groups, proximate composition and GSI is also available for species like North Sea herring and mackerel. In addition data on size groups is available for ground&h like cod, saithe and haddock. However, the usefulness of these data remains to be evaluated.