Understanding Otter Trawls: Design, Function, and Sustainable Fishing Practices

Otter trawls are a primary method used in commercial fishing to catch bottom-dwelling fish such as cod, haddock, and flounder. These large, cone-shaped nets are towed behind fishing boats, skimming along or just above the seabed. The design of the otter trawl is specialized to maximize efficiency while targeting specific fish species.

The mouth of the net is designed to stay open while it is being towed. This is achieved by attaching floats to the top of the net and weights to the bottom. These components create a vertical opening, ensuring the net remains open as it moves through the water. Horizontally, the net is kept open by “doors,” which are large rectangular wooden frames attached to the towing lines on either side of the net’s mouth. These doors spread the net wide, increasing the area it can cover and allowing for a more effective capture of fish.

The far end of the otter trawl, known as the "cod end," is constructed with a mesh size that is small enough to retain fish of edible size while allowing smaller, juvenile fish to escape. This design is critical for promoting sustainable fishing practices, as it helps prevent overfishing of young fish that have not yet reached maturity.

After a period of towing, the net is hauled back to the boat. The cod end is then secured with a strap and lifted out of the water. A specialized mechanism allows the bottom end of the net to open, releasing the fish onto the deck. This efficient process minimizes handling time, reducing stress on the catch and ensuring the freshness of the fish for market.

Recent advances in trawl design and technology have focused on improving selectivity and reducing bycatch, further supporting sustainable fishing efforts. Additionally, ongoing research aims to minimize the environmental impact of trawling on seafloor habitats, balancing the demands of commercial fishing with the need for conservation.
Understanding Otter Trawls: Design, Function, and Sustainable Fishing Practices

The Cod

The Cod
Cod are found on both sides on both sides of the Atlantic and are most plentiful around Norway, Iceland, Newfoundland, Nova Scotia, and on Georges Bank off Cape Cod. In the Western Atlantic, they range from Greenland to North Carolina. Molluscs (clams, oysters, scallops, etc) are said to make up an important part of the diet of the cod, but cod also eat small fish.

By far the largest quantities of cod are caught with otter trawls in waters ranging from 300 to 1500 ft in depth. Small quantities of this species are caught with long lines, hand lines, or grill nets. When caught with otter trawls, the fish are gutted and washed on the deck of the boat. During summer months, the gills must be removed, but the head is left intact. The fish are stored in boxes or pens, in either case layered with ice.

At the processing plant, the fish are washed and filleted, skinless. The fillets are then candled (observed over a bright light) to locate and removed parasites. Fillets to be sold as fresh precooled, placed in metal tins of 10, 20, or 30 Ib, and the tins are refrigerated (mechanically or in ice) until they reached their destination. Some fillets are precooled, packed in small trays. Overwrapped with the transparent plastic, and shipped to their destination in insulated containers.
The Cod