Bottom trawling is a common method for catching bottom-dwelling species such as shrimp and flounder. This involves dragging heavy gear across the sea floor, which destroys habitats and captures many non-target species. Bottom trawling equipment has been described as the most destructive fishing gear in use today (Watson 2006). Boats are equipped with large, heavy nets that are dragged across the living seafloor. The nets are held open at the front by a metal beam or by large “doors,” which can weigh several tons and are designed to scour the bottom as the trawl is dragged along. This process takes a heavy toll on the natural habitats of the sea floor, breaking off brittle bottom fauna such as sponges and corals.
In addition to disrupting the living seafloor, trawling kills large numbers of animals as by-catch, the accidental harvest of untargeted species such as other fish and invertebrate species, marine mammals, seabirds, and turtles. Some of this by-catch is retained for sale, but a portion of it is returned to the sea as discards, usually dead or dying. Bottom trawled fisheries have the highest discards rates of all fisheries.
The habitat destruction caused by trawling directly affects the human communities that depend on marine resources for food and income. When nursery habitats such as seagrass beds are destroyed, the entire local environment is impacted and the productivity of local fisheries decreases.
The 2008 EPI Trawling Intensity indicator consists of the percentage of the shelf area in each country’s EEZ that is fished using trawling. There are no direct data available for the area trawled on a country-by-country basis. However, fish landings data are acceptable as a proxy for each country’s fishing fleet. Thus trawling ships can be counted and incorporated into this trawling metric. The target level selected for this indicator is 0% area trawled, reflecting the opinion that any use of this fishing method is ecologically undesirable.
