Dataset: Improving the Size Selectivity for Northern Shrimp Through Use of a Combination of a Modified Nordmore Grate and Square Mesh Cod End: tows from the F/V Jeanne C, Gulf of Maine, 2003-2004 (NEC-CoopRes project)

Improving the Size Selectivity for Northern Shrimp Through Use of a Combination of a Modified Nordmore Grate and Square Mesh Cod End

Final report by Daniel Schick, Kelo Pinkham and Lessie White.

This dataset lists all trawl modifications and test dates. See also:
*shrimp_nord_sumry - summarizes the test results for the various trawl modifications, with statistical analysis.
*shrimp_nordgrate - large and small shrimp catch data

Abstract

Comparative tows with a trouser trawl were conducted to test improved release of small shrimp and fish and retention of large shrimp using various configurations of a compound Nordmore grate and diamond or square mesh in the lengthening piece and cod end. The forward (upper) grate section had small bar spacing (7/16") sized to allow small shrimp to flow between the bars and escape. The aft (lower) section had ¾" bar spacing to allow large shrimp to flow between the bars and into the cod end mounted behind this section. Two sizes of small bar space section, ½ and ¼ of the total length were tested. The ½ length section released more small shrimp but also retained less large shrimp than the ¼ length section compared to a standard Nordmore grate/cod end. The large shrimp were flowing out the escape hole at the bottom of the compound grate. The aft section was lengthened for better retention of large shrimp and the small bar space section was tilted (bent) another 10 degrees to improve small shrimp release. A small bar space section with tapered openings was added to the test series as was square mesh in the lengthener and/or cod end. The two modified compound grates with the four mesh combinations produced eight test series where each gear type was judged for finfish release, shrimp weight retained, small shrimp release and large shrimp retention. The best combination was the 7/16" bar space bent grate with diamond lengthener and square mesh cod end.