Although rare, sharks have been known to attack and kill dolphins, while there has also been evidence of killer whales eating dolphins, says the National Aquarium, a website run by Bio Expedition. Since dolphins are on the top of the food chain, few animals are considered as their enemies.
The National Aquarium, further states that humans are the biggest threat to dolphin lives. In Japan, dolphins are considered a delicacy and are hunted for culinary purposes, while some fishermen kill dolphins because they prey on smaller fish and ruin their catch. However, the most dolphin deaths are contributed to accidents during large-scale tuna-fishing operations. Tuna fishing is considered especially hazardous to dolphins because large schools of tuna swim below dolphins. Although surviving dolphins are usually released back into the ocean, Dolphin's World estimates that large fishing expeditions have killed at least 30 million dolphins since 1960.