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Bottom Trawls: Fishing Gear and Risks to Protected Species

NOTE: Gear types are listed by broad category. They are not intended to be specific to regional fishing practices.

Bottom trawling is a fishing practice that herds and captures the target species, like ground fish or crabs, by towing a net along the ocean floor.

Floats are attached to the headrope, top of trawl opening, while weights and special gear are attached to the footrope, bottom of trawl opening, to keep the net open as it moves through the water across the ocean floor. The mesh is designed to confine fish inside the net, trapping them in the codend as the trawl is hauled to the surface. A sweep attached to the net's footrope collects marine animals as they lay on the bottom or gather before the trawl opening. The trawl gear may be constructed and rigged for various target species over different types of bottom surfaces. Sweep types include:

 

Bottom Trawl
Bottom Trawl
Credit: Food and Agriculture Organization of the United Nations (FAO)


 


 typical_trawl
Midwater Trawl
Credit: Food and Agriculture Organization of the United Nations (FAO)


 

Target Species

Fisheries Regions

Risks to Sea Turtles

Many sea turtle species rest and forage on the bottom and are at risk of being captured in bottom trawls. Capture in a bottom trawl could result in:

Risks to Marine Mammals

Marine mammals can become entangled by trawl gear when swimming to forage or migrate, with risks differing widely between species. Species that forage on or near the sea floor are at risk of being captured or entangled in netting or tow lines (also called lazy lines). 

Pilot whales and common dolphins in the Atlantic are particularly susceptible to being caught in bottom trawls.

Bycatch Reduction

Sea turtle mortality in trawl gear was once very high. Turtle excluder devices (TEDs) have greatly reduced these risks in some trawl fisheries and might even allow small cetaceans to escape as well. TEDs are currently only required in trawl fisheries targeting shrimp and summer flounder.

Some recommended voluntary mitigation measures [pdf] for reducing marine mammal bycatch include:

Additional Resources

Updated: January 30, 2014