| Summary: | In demersal trawls the most commonly used codends are diamond-mesh. However, diamond-mesh codends is discovered to vary in mesh geometry which lead to a less well-defined size selection process. One alternative often adopted to reduce variability in mesh geometry, and thereby obtain a sharper size selection, is to force the meshes to adopt a square geometry by turning the codend netting 45 degrees (T45 standard square-mesh). Therefore, we tested the size selectivity of a standard square-mesh and a standard diamond-mesh codend and a fixed diamond-mesh codend whose mesh geometry was optimally defined to suite the morphology of cod. Using Atlantic cod (Gadus morhua) as a case study, we found no evidence that the square-mesh codend had lower variability in size selection than a standard diamond-mesh codend with same mesh size. Moreover, we demonstrated that the square-mesh codend had significantly larger variability in size selection compared to what was obtained with a codend where the mesh geometry was kept fixed during the fishing process. These results demonstrate that the use of square-mesh codends is not a sufficient strategy to reduce the variability in codend size selection. On the contrary, this would need a codend construction where the mesh geometry is kept constant during fishing, thus providing a new engineering challenge for the development of commercial trawl gears.
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