Scientists have attached satellite tags to eight walruses in west Greenland to find out where they are migrating over the summer months.
The walruses were spotted from a 70-tonne trawler by field leader Mikkel Villum Jensen and the boat's crew. The trick was to find a brown blob on the white, ice-covered sea.
At this time of year, walruses are lazing about on the ice soaking up vitamin D from the Sun, resting after they have fed on clams and other molluscs from the seabed.
Almost all of the tags were deployed from a skiff that made much less noise than the trawler as it approached the creatures.
Field leader Mikkel Villum Jensen said that the easiest way to attach the tags to the walruses was if they were sitting on the ice, like this one with its infant.
But most of the time, even when in the smaller boat, the walruses slipped into the water at the slightest sound, making attaching the tags much more difficult.
The tags were deployed with three instruments: a crossbow, a CO2-powered gun, and a harpoon that the skipper had made.
Trying to deploy the sat tags in -10 to -25C (14 to -13F) conditions with strong winds and snow was difficult. Some of the walruses, such as this old bull, got away without a tag.
But eight other walruses were tagged, and now scientists will be able to find out exactly where they spend the summer months.
Mr Villum Jensen said he was extremely pleased: "The conditions have been harsher than we had anticipated and we lost two of the tags but overall I'm very happy."