Contribution of different spawning components to the mixed stock fishery for cod in Icelandic waters

Otolith chemistry and length-at-age were used to estimate the contribution of different spawning components to the harvested stock of cod (Gadus morhua) at two of their main feeding grounds northwest and east of Iceland. Spawning cod were sampled at different spawning locations around Iceland in spring of 2002 and 2003. Significant differences were detected between cod from the different spawning locations. Cod of unknown stock origin were also sampled at two of the main feeding grounds in October of the same years. Analyses based on maximum likelihood were used to estimate the proportion of each spawning group in the mixed stock catches using otolith chemistry and fish length-at-age. Attempts to use otolith shape to estimate the contribution of the spawning groups to the mixed harvested stock were, however, unsuccessful. The results indicated that spawning locations northwest and north of Iceland, as well as in water deeper than 125 m south of Iceland, contributed the most to the harvested stock. Cod spawning shallower than 125 m south of Iceland did not contribute to the feeding grounds in October of 2002 and 2003. Therefore, exploitation of the feeding stock mixtures seems to be based on spawning components that have previously been considered to be of minor importance to the Icelandic cod stock.