Trawl Net Design and Mesh Regulations

A trawl is a cone-shaped net towed through the water or dragged along the bottom, and its mesh size at the codend is the single parameter fisheries managers use to control which size classes of fish escape versus are retained. Diamond mesh of 40-60 mm is typical for shrimp trawls, while demersal finfish trawls targeting cod or haddock commonly run 100-130 mm square mesh, since square mesh stays open under tow tension and lets undersized fish swim out far more effectively than diamond mesh, which collapses closed. Regulations set minimum mesh size by target species and region, often paired with bycatch reduction devices such as turtle excluder devices or fish escape panels. Net material (polyethylene versus nylon), headrope-to-footrope ratio, and otter board spread all affect how wide and how close to the seabed the net fishes, which in turn determines species selectivity and seabed contact. For seafood buyers and processors, trawl gear type correlates with product condition on arrival: towed too long or too deep, catch arrives crushed and bruised, lowering fillet grade before it ever reaches the plant.