1. Department of Biological Sciences, University of Bergen , 5020 Bergen , Norway
2. The Norwegian Institute for Nature Research , 7485 Trondheim , Norway
3. Faroe Marine Research Institute , FO-110 Tórshavn , Faroe Islands
4. National Institute of Aquatic Resources, Technical University of Denmark , 9850 Hirtshals , Denmark
5. Institute of Marine Research , 5005 Bergen , Norway