The polar bear is at the top of the food chain for arctic animals, helping to control the seal population by feeding almost exclusively on seals. Polar bears rely on the high fat content of seals to fuel their bodies and maintain good levels of needed fat within their own bodies.
Polar bears may eat beached whales, fish or smaller animals during times of low food sources. Eating these other animals is done out of necessity and not because of a preference for fish or small prey.
Grown polar bears have no predators other than other polar bears. Polar bear cubs are at risk of being eaten by other malnourished polar bears, but the adults are at the top of the food chain.