By the turn of the 20th century, commercial fishing was gaining a foothold in the Aleutian Islands. Packing houses salted cod and herring, and salmon canneries were opened. Another commercial occupation, whaling, continued with no regard for over-hunting. They pushed the bowhead whales to the edge of extinction for the oil in their tissue. The Aleuts soon suffered severe problems due to the depletion of fur seals and sea otters which they needed for survival. As well as requiring the flesh for food, they also used the skins to cover their boats, without which they could not hunt. The Americans also expanded into the Interior and Arctic Alaska, exploiting the furbearers, fish, and other game on which Natives depended.