The use of otolith chemistry to determine the juvenile source of spawning cod in Icelandic waters

Chemical fingerprinting was used to discriminate spatial groups of juvenile cod (Gadus morhua) and to backtrack spawning cod in Icelandic waters to their area of origin as 0-group juveniles. Juvenile 0-group cod were collected around Iceland in August 1996 and 1997 to establish the spatial distribution of otolith chemistry at the juvenile stage. Spawning cod from the same year classes were sampled in the same areas in April 2002 and April/May 2003. The core, corresponding to the juvenile otolith, was extracted from the adult otolith and its content of Ba, Mn, and Sr compared with the chemistry of whole otoliths of juveniles of the same year class. High Atlantic inflow into the shelf area north of Iceland in 1997 mixed the juveniles from different areas, and the spawners of that year class were not backtraceable to their origin. For the 1996 year class, however, mixed-stock analysis indicated that most of the spawning cod northwest, north, and northeast of Iceland originated from juveniles off the central part of the north coast. Using otolith chemistry to backtrace the origin of spawners appears well suited for areas with limited mixing, but less well suited for areas or years of high current velocity.