Neolithic people gathered shells, fished, and threw harpoons and nets in the seas and rivers. The South Sea is rich in biological resources thanks to warm currents. The remains of fish (such as red sea bream and sharks), marine mammals (such as whales), and shellfish (such as oysters, mussels, and abalone) were found in the Dongsam-dong shell midden. In the shell middens of the West Sea, oyster shells are dominant. Fish may have been trapped and caught in stationary nets by utilizing the incoming and outgoing tides. In the deeper waters of the East Sea, fishing may have involved the catching of salmon as they migrated from the seas into the rivers.