We usually think about tracking objects, more than we do about how they are actually tagged. This BBC picture documentary shows the process scientists went through to tag walruses for observation. The best quote is, “The tags were deployed with three instruments: a crossbow, a CO2-powered gun, and a harpoon that the skipper had made.” You can follow the tagged walrus migration through the “Walrus Watch” map and website, “showing the animals’ day-to-day progress during the two-month project”