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Pilot Pilot Project to Design and Test a Low-Impact Scallop Dredge


Low-impact Scallop Dredge

Project summary:  Commercial diver Paul Tasha approached Michael Pol at the Massachusetts Division of Marine Fisheries (DMF) and Olivia Free at the Massachusetts Fishermen's Partnership (MFP), and then Cliff Goudey at Center for Fisheries Engineering Research (CFER), MIT Sea Grant College Program, with some ideas on a novel approach to harvesting scallops aimed at reducing the habitat impacts associated with current scallop dredging methods. Mr. Tasha’s ideas were based on experiments he conducted on what moves and lifts scallops off of the sea bottom. He found that the passage of a diver’s hand or a circular disk over a scallop seems to work consistently. What Mr. Tasha discovered is important in meeting the recognized need for better methods of harvesting scallops. Our novel approach to scallop harvest exploits hydrodynamic flow to elevate scallops and reduce contact between the gear and the seabed. Tests in the MIT ocean engineering tow tank evaluated a wide range of shapes to see how well they lifted scallop models off of the bottom. Low-aspect-ratio shapes (downward-facing cups) produced the greatest effect. A seven-foot wide wheeled prototype dredge was designed using the cup shapes and no cutting bar. It was built and tested onboard the F/V Pretty Girl, a commercial scallop vessel. Underwater video was used to record the response of scallops and other benthic organisms to the passage of the dredge. The in-situ video showed a downward jet of water and large-scale vorticity generated by the cups. The dredge deployed easily, seemed to tow easier, and resulted in a 30% to 50% catch rate compared to that of a properly tuned conventional dredge. The next steps include rigorous fishing trials to determine catch and bycatch rates, habitat impact comparisons, research to reduce impact of the chain bag, and dredge scale-up for testing onboard offshore commercial fishing vessels. This project was funded by the Northeast Consortium.

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Project partners:
Clifford Goudey, MIT Sea Grant College Program
Michael Pol, Massachusetts Division of Marine Fisheries
Paul Tasha, Commercial Diver
Olivia Free, Massachusetts Fishermen's Partnership
Captain Louis Williams, F/V Pretty Girl

 

 

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