1. Department of Aquatic Resources; Institute of Marine Research; Swedish University of Agricultural Sciences; 45330 Lysekil Sweden
2. Department of Fisheries Oceanography and Marine Ecology; National Marine Fisheries Research Institute; 81332 Gdynia Poland
3. National Institute of Aquatic Resources; Technical University of Denmark; DK-2920 Charlottenlund Denmark
4. Department of Earth Sciences; University of Gothenburg; 40530 Gothenburg Sweden