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How does dredging catch mollusks and crustaceans from the seafloor?
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commercial fishing
Worker in the Tsukiji fish market, Tokyo.
In commercial fishing, dredges are specialized gear used to harvest mollusks and crustaceans from the seafloor. These devices function by being towed along the bottom, where they collect their catch into a bag or container.1
The design of a fishing dredge varies based on the target species and seafloor conditions:
- Mechanical Dredges: The simplest versions are hand-operated, resembling rakes attached to a collection bag. Larger, vessel-towed versions feature a triangular or quadrangular iron frame. To assist in digging out mollusks, these frames may be equipped with iron teeth on the lower edge. The collection bag is typically constructed from durable wire rings and hard-fibre netting to withstand friction against the seabed.1
- Hydraulic Dredges: These advanced machines use high-pressure water jets to wash deeply buried shellfish, such as soft clams or cockles, out of the sediment. Once dislodged, the catch is often transported to the surface via conveyor belts or pumps.23
While effective for harvesting, dredging is often criticized for its environmental impact, as the gear can damage the seafloor and unintentionally harm or kill other marine life.14