| dc.description.abstract | 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. | en |
