Ringed seals are one of the most important species to be used by Inuit. As food, clothing and equipment materials, and sources of fat used for fuel, the ringed seal is indispensable. Because its sense of vision is poor, ringed seals are stalked from upwind behind a blind of white canvas or polar bear skin. The age of the ringed seal can be determined by the layers which form on their teeth each spring; by this method, some have been found to be as old as 43. The species feeds mainly on crustacean macroplankton, crabs, prawns, and fish. They will sometimes consume krill in deeper water. Ringed seals are preyed upon by sharks, orcas and polar bears, while arctic foxes and even gulls will claim young pups.