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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.
Read Full Report
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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