Migratory behaviour of Greenland shark (Somniosus microcephalus)

The study examines the migratory behaviour and population affiliation of Greenland shark (Somniosus microcephalus) in North Norway. A total of 120 animals are caught by scientific long-lines and carefully lifted to the surface. At surface, animals are tagged externally with either satellite tags (N=20) or conventional tags (N=100), total length is measured and a dorsal fin biopsy is taken for genetic ID. The entire procedue from retrieval to release lasts about 15 min per animal. The animals never leave the water and are deemed only slightly affected by the handling. After a specified period of 3-6 months post-tagging, the satellite tag is released from the animal, pops to the surface and transmits data about spatial distribution, ambient light and temperature. The conventional tags, on the other hand, are retrieved only if animals are recaptured accidentally in bycatch etc. Empirically, about 120 tagged animals over three years are needed to reduce the uncertainty of retrieving tags and data. For example, satelitte tags may be lost beneath the sea-ice and animals with conventional tags are either not recaptured or tags are overlooked in catches. Greenland shark is classified DD (data deficient) in the Norwegian Redlist (2015) and any information on its whereabouts is of utmost importance to design proper conservation and management actions for this little known species.