Tagging walruses in the Arctic

Scientists have been attaching satellite tags to walruses in West Greenland to track their movements.

They want to find out where the tusked beasts migrate to over the summer months - at the moment the creatures simply vanish off the radar.

This footage, filmed during the 2007 expedition, shows the matchbox-sized devices being attached to the walruses' thick skin with a CO2-powered gun.