More than 6000 cod Gadus morhua, sampled in coastal and offshore waters stretching from the Barents Sea down to the North Sea, were analysed for frequencies of alleles at the scnDNA pantophysin locus (Pan I) [formerly called synaptophysin (Syp I)]. The significant allele frequency difference between the two major stocks of cod in Norway, north-east Arctic cod (NEAC) and Norwegian coastal cod (NCC), was upheld in all years of the investigation (1993 to 2001), and applied both to larval cod and post-juveniles of various ages. On a north-south axis, the appearance of a latitudinal cline of post-juvenile (!1 year) allele frequencies was exposed. The intermediate allele frequencies in coastal areas of northern Norway, seem to a large extent to be caused by intermingling of the two stocks, although the existence of populations of coastal cod with alternative Pan I frequencies could not be ruled out. The role of selection is yet unresolved. Depth of the sampling location seemed to have an effect on the allele frequencies and their temporal stability, while there was no indication of seasonal variation in the frequencies. Breeding structure was the most likely cause for upholding the extreme divergence in Pan I frequencies between NEAC and NCC. # 2005 The Fisheries Society of the British Isles

The distinction between north-east Arctic cod and Norwegian coastal cod, two major groups of Atlantic cod (Gadus morhua L.), has for many years been based on different distance and shape similarities between the two first translucent growth zones in the otoliths, subjectively decided by visual inspection in a binocular. To analyse the certainty of this technique, four independent readers have classified 263 cod otoliths in total from five different geographical areas. For three of the readers, between 82% and 89% of the classification results coincided with independent results based on genetic analyses. Further, 38 cod otoliths, where the readers were certain of the classification (21 north-east Arctic cod and 17 coastal cod) were classified by several image analysis methods. A complete separation was obtained by using the ratio of the circumferences of the two zones, providing a typical ratio of approximately 2 for coastal and 1.5 for north-east Arctic cod. The otolith method for separating the two types of cod has been considered adequately accurate in assessing the two stocks of cod. However, the method is sensitive to subjective interpretation, and action needs to be taken to minimise the difference in interpretation among otolith readers.

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