Porpoises eat many kinds of fish, squid, octopus and other ocean creatures. Their specific diet is influenced by where they live and what kind of fish are available to them, but they always eat a fairly varied diet.
There are six different types of porpoises, not all of which have been thoroughly studied as of 2015. It is possible that their diets vary. However, all of the well-known species have similar diets, so it is likely that the lesser-known ones do as well.
Porpoises also eat crustaceans, shellfish and cuttlefish. Porpoises sometimes live or hunt in rivers, which allows them to eat crayfish. Smaller porpoises may focus on small schooling fish, but they generally eat any type of non-spiny fish. Porpoises need to eat a lot; harbor porpoises, for example, eat up to 10 percent of their body weight every day.
Porpoises hunt using echolocation, which means they make low-frequency clicking sounds and use the reflected sound waves to help find their prey. They use their teeth to catch fish but do not chew them, so fish need to be small enough for them to swallow.
Porpoises are sometimes preyed upon by killer whales or other sea mammals. They also are often accidentally killed by fishing nets; when hunting, they become so focused on catching their prey that they do not see the nets.