Sharks are the most successful predators in the ocean. Their only real enemies are other sharks and humans. Of these two, humans are the only serious threat to the migration success of sharks.
Humans threaten sharks and their migration success in several ways.
These include killing sharks for their commercial value, for sport, in response to the media, and to protect swimmers at public beaches. Sharks do feed on each other, though this is less likely than we would think since sharks are highly specialized hunters with preferred food sources. Humans are the only really serious predators affecting shark survival. Because they are strong ocean swimmers, sharks are able to escape unharmed from many environmental events that will do serious damage to slower or more fragile animals lower on the food chain. For example, due to its keen sense of smell, swim speed and strength, a shark is likely to identify and swim around an oil spill.