This involves using nets, fishing methods and other equipment that catch too much fish to a degree that they are endangered. It also involves catching other sea animals other than fish in the process. These are called By-catch. In many cases by-catch is destroyed and thrown back into the sea. This is called Discards, and may include cetaceans, turtles, sharks, seabirds, youngfish, corals and invertebrates like starfish, crabs, sea urchins, brittle stars, mollusks, sponges and worms. They also catch very little fishes and prevent them from growing to reproduce.