The size selectivity of four codends were compared in the Gulf of St. Lawrence, Canada redfish fishery, including the regulated diamond mesh codend with a mesh opening of 90 mm (T0) and three experimental codends of different mesh openings (90, 100, 110 mm) in which the netting is turned 90° to the direction of tow (T90). Results for the regulated codend showed that there was little size selection, catching greater than 97% of redfish over all of the length classes observed. Considering the fished population, the smallest T90 codend would catch 30% fewer redfish under the Minimum Landing Size (MLS) of 22 cm compared with the T0 codend, but would also lose 16% of catch above 22 cm. The T90 codend with 100 mm mesh opening had the same size selectivity as the smallest T90 codend. The 110 mm T90 codend would catch 50% less redfish below MLS but lose 40% of redfish above. Overall, results show that T90 codends improve size selectivity in which large proportions of undersized fish are successfully released.

A B S T R A C TIncreasing regulations, bycatch restrictions, and concerns over ecosystem impact are now the driving forces for much of the development in fishing gear design occurring world-wide. Industry, government, and universities have responded to these challenges with major advancements in computer aided design, simulation, physical modeling techniques, and worldclass testing facilities. Model studies are a critical step in the development of new fishing gears and flume tanks are the de facto standard for investigating their attributes and performance under controlled conditions. This paper discusses the nature of flume tanks, their attributes, as well as the science and art of building and testing scale models of fishing gear. Footnote

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a b s t r a c tA Canadian demersal survey trawl (Campelen 1800) was used to investigate the differences in trawl geometry and resistance using dynamic simulation, flume tank testing, and full-scale at-sea observations. A dynamic simulation of the trawl was evaluated using DynamiT software. A 1:10 scale model was built and tested in a flume tank at the Fisheries and Marine Institute of Memorial University of Newfoundland (Canada). Full-scale observations of the Campelen 1800 in action were collected during the 2011 fall multi-species survey aboard the research vessel CCGS Teleost. The numerical and physical modelling data were assessed to determine their ability to predict full-scale at sea performance of the Campelen 1800 trawl. The numerical simulation data were also compared against scale model engineering performance under identical conditions. The study demonstrates that the ideal method with which to accurately predict full-scale at-sea performance of bottom trawls or used for designing a trawling system probably does not exist. Therefore, the importance of using two or three complementary tools should be encouraged as an ideal process for designing a trawling system and/or assisting the gear development circle.