Reduction of Finfish and Juvenile Shrimp....
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GRANT NUMBER:  NA76FD0097           NMFS NUMBER:  96-NER-079

REPORT TITLE:  Reduction of Finfish and Juvenile Shrimp Bycatch in the Gulf of Maine Northern Shrimp Fishery through the Use of a Modified Double Nordmore Grate

AUTHOR:  Daniel Schick, Michael Brown, David Gallagher, and Ronald Shepard

PUBLISH DATE:  May 10, 1999

AVAILABLE FROM:  National Marine Fisheries Service, Northeast Regional Office, One Blackburn Drive, Gloucester, Massachusetts 01930-2298.   PHONE:  (978) 281-9256


Shrimp fishermen in the Gulf of Maine are required to use a finfish excluder called a Nordmore grate.  This single grate is very effective at releasing large fish from nets, but it is not very good at releasing finfish similar in size to shrimp.  Prior work showed some success in reducing the catch of submarket-size shrimp by the addition of a second Nordmore grate, with the second grate releasing the small shrimp.  The double Nordmore grate system was tested for the bar spacing in the second grate that would release the most small shrimp without reducing the catch of market-size shrimp.   Trials with bar spaces of 1/4" (6.4 mm), 5/16" (7.9 mm), 3/8" (9.6 mm), 7/16" (11.1 mm), and 1/2" (12.7 mm) showed that 1/2" provided the best escapement of small shrimp but allowed too many large shrimp to escape also.  The 7/16" bar spacing gave the best combination of retention of large shrimp and release of small shrimp.  None of these trials showed measurable differences in escapement of small finfish through the bars of the second grate.  The 1/2" bar spacing was used in tests of two additional devices designed to improve the escapement of small shrimp and finfish bycatch that still made it to the cod end.  These devices were hoops designed to spread the mesh in the cod end and water scoops on either side of the second grate designed to increase the water flow through the cod end.  In the tests, neither device improved the escapement of shrimp, nor did they appear to improve the escapement of finfish.  Unexpectedly, the hoops retained more shrimp than the controls in all cases, possibly due to reduced water flow through the individual meshes.  Two further modifications--the addition of a funnel between the grates and the use of square mesh in the cod end--did not substantially increase the separation of small shrimp from the catch.


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