Bottom trawling is trawling (towing a trawl, which is a fishing net) along the sea floor. The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towing a net at the very bottom of the ocean and demersal trawling is towing a net just above the benthic zone. Bottom trawling can be contrasted with midwater trawling (also known as pelagic trawling), where a net is towed higher in the water column. Midwater trawling catches pelagic fish such as anchovies, tuna, and mackerel, whereas bottom trawling targets both bottom living fish (groundfish) and semi-pelagic species such as cod, squid, shrimp, and rockfish. Trawling is done by a trawler, which can be a small open boat with only 30 hp or a large factory trawler with 10,000 hp (7,500 kW). Bottom trawling can be carried out by one trawler or by two trawlers fishing cooperatively (pair trawling).