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Why can dredging damage part of the catch before it reaches the vessel?

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A worker in dark clothing inspects large frozen tuna lined up on the floor at Tsukiji fish market in Tokyo, Japan, using a tool to check the fish. — commercial fishing Worker in the Tsukiji fish market, Tokyo.

Dredging is a method used in commercial fishing primarily to harvest mollusks and crustaceans from the seafloor. The process involves towing a heavy iron frame—often equipped with iron teeth on the lower edge to dig into the substrate—along the bottom of the sea.

The significant disadvantage of this technique is that it frequently damages the catch before it reaches the vessel. This damage occurs because the mechanical action of the dredge, which includes dragging the heavy frame and its components across the seafloor, is inherently destructive. The physical impact of the iron frame and teeth, combined with the friction generated as the dredge is pulled along the bottom, often crushes or injures the organisms being targeted. This results in wasted effort and the unnecessary killing of marine life that may not be suitable for market once damaged.1