Life history of turbot in Icelandic waters: Intra- and inter-population genetic diversity and otolith tracking of environmental temperatures

The stock structure of turbot was investigated between samples from S-Norway, the Irish Sea and theKattegat, using 12 microsatellite loci and compared to the turbot caught in Icelandic waters. Highly sig-nificant genetic differentiation was observed between samples from Kattegat and other areas. Significantgenetic differentiation was also observed between the Irish Sea sample on one hand and Iceland andS-Norway on the other hand. No significant genetic differentiation was observed between Iceland andS-Norway. Otoliths of 25 turbot, age ranging from 3 to 19 years, were subjected to nearly 300 mass spec-trometry determinations of stable oxygen and carbon isotopes. Oxygen isotope composition (18O) inthe otolith samples was used to estimate ambient temperature at time of otolith accretion, and yieldedestimated temperatures experienced by the turbot ranging from 3 to 15◦C. Overall, the genetic analysisindicates panmixia between turbot in Icelandic and Norwegian waters. While the extensive migration oflarvae between Norway and Iceland is unlikely, passive drift of turbot larva from other areas (e.g. Ireland)cannot be ruled out.