Bottom-trawl fishing provides about a quarter of global seafood but is controversial. The heavy nets and dredges that are used to catch species like cod, plaice and scampi also disturb the seabed and kill some of the invertebrates that live there. For instance, a single pass with the widely used "otter trawl" kills about 6% of seabed animals, while a scallop dredge kills closer to 14%.