From the BBC:
Danish scientists plan to put satellite tags on walruses to understand more about their migration, and how hunting, oil exploration and climate change may be affecting the animals.
GPS systems will be deployed using a cross bow or CO2-powered gun fired from the boat. Each time they emerge from the water, a signal will be beamed up to a satellite, giving details on the the walruses' location. For two months, readers of BBC news will be able to map the progress of the animals on the Walrus Watch map.