Blue whiting (Micromesistius poutassou) stock components in samples from the northern Norwegian Sea and Barents Sea, winter 2002

No abstracts are to be cited without prior reference to the author.

Blue whiting from the eastern parts of the Barents Sea are genetically different from other parts of the northeast East Atlantic, indicating the existence of a self-sustaining and reproductively isolated or semi-isolated stock there. In mid- and western Barents Sea, its geographic distribution may overlap with Hebrido-Norwegian blue whiting on summer feeding migration. Circumstantial evidence from egg- and larvae distributions supports such a stock structure. Based on observation of unusually large amounts of young blue whiting in the northwest Barents Sea in 2000 and 2001, a sampling scheme encompassing the entire Barents Sea was designed and carried out in winter 2002 to explore the stock origin of these. The polymorphic isozyme loci PGM-1* and IDHP-2*, which showed discriminatory power in earlier blue whiting studies, were employed. The genetic analyses did not reveal overall genetic heterogeneity among geographic samples, but more detailed analysis revealed a statistical significant heterogeneity between age groups. At both loci, allele frequencies in Blue whiting four years and older were different from those in younger age groups, which in turn showed allele frequencies similar to those in the Hebrido-Norwegian stock. Hence, the younger specimens in the blue whiting occurrences in the northwest parts of the Barents Sea in 2001-2002 appear to origin with the Hebrido-Norwegian stock, while the older ones showed genetic characteristics like those of the previously reported Barents Sea stock. The possibility of physical population mixtures by different age groups is a novel feature which must be considered in genetic analyses of blue whiting.