1. Molecular Ecology and Fisheries Genetics Laboratory, School of Natural Sciences, Bangor University, Bangor, Gwynedd LL57 2UW, UK
2. Population Genetics Research Group, Institute of Marine Research, P.O. Box 1870, Nordnes, NO-5817 Bergen, Norway
3. Matre Research Station, Institute of Marine Research, Matredal, Norway
4. Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK
5. School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
6. Institute of Biology, University of Bergen, N-5020 Bergen, Norway