Bottom trawling is a type of fishing in which a large net is dragged along the bottom of the ocean. Weights keep the net at the bottom of the seafloor while a set of floats on the top keep it open. This type of fishing targets bottom-dwelling species like flounder and crabs. Both sea turtles and marine mammals are at risk of becoming entangled in this type of gear, though turtle excluder devices (or TEDS) are required on nets in the United States in the shrimp and summer flounder fisheries. Bottom trawls are some of the worst fishing gear when it comes to bycatch—as of 2019, about 46 percent of all bycatch comes from bottom trawls.