Size selective performance of two flexible sorting grid designs in the Northeast Arctic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) fishery.

The flexigrid is a flexible double grid design and is one of the mandatory selection devices used in the Northeast Arctic cod ( Gadus morhua ) and haddock ( Melanogrammus aeglefinus ) fishery. Traditionally the flexigrid is mounted in a two-panel extension section of a trawl just ahead of the codend, but this design has performance limitations, especially during high volume catch situations. The aim of this study was to investigate the size selective properties of a new four-panel section design for the flexigrid and compare them to those of the traditional two-panel section. Specifically, we wanted to determine if this new design would increase the probability for undersized fish to make contact with the grid and subsequently escape through at least one of the two grids in the section. We quantified the parameter “grid contact” for both grids independently and combined for both the mandatory two-panel and the new four-panel designs. We directly compared the two designs using a single trawl with a three compartment experimental design which enabled estimation of the contribution of each of the grids to the combined selectivity of the flexigrid section. The results based on 51 hauls with 108,518 cod and haddock length measurements indicate that the four-panel flexigrid design was better able to release undersized fish than the two-panel design. While the mean values of “grid contact” estimated for both grid designs were similar, the four-panel section had lower risk of clogging in situations of high fish entry rates. Underwater video recordings revealed that the cause for this difference between designs may be related to the difference in shape of the two sections while fishing. The results showed that undersized cod escape mostly through the lower grid of the flexigrid section, whereas haddock generally utilize the upper grid. This finding is in good agreement with the behavioral differences previously described for these two species. Due to the favourable results obtained from this study, the four-panel flexigrid section is now legalized in the Northeast Arctic cod and haddock fishery. [ABSTRACT FROM AUTHOR]