Make it simpler and better: T90 codend improves size selectivity and catch efficiency compared with the grid-and-diamond mesh codend in the Northeast Atlantic bottom trawl fishery for gadoids

Abstract

The use of a sorting grid followed by a size-selective codend with minimum 130 mm mesh size is compulsory in the Northeast Atlantic demersal trawl fishery targeting cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and saithe (Polachius virens). However, sorting grids cause some disadvantages, which possibly can be solved by removing the grid and improving codend selectivity, thus making the construction simpler. This study compared the size selectivity and catch efficiency of two diamond-meshed codends turned 90° (T90) with two different mesh sizes (135 and 145 mm) with those of a sorting grid followed by a diamond-mesh codend. The results showed that the T90 145-mm codend caught 7.0% fewer cod and 8.2% fewer saithe above the minimum reference length (MRL) compared with the compulsory configuration. By contrast, compared with the compulsory configuration, the T90 135-mm codend increased the capture of cod above the MRL by 4.4%, from 80.4% to 84.8%, of haddock by 14.1% from 45.2% to 59.3%, and of saithe by 16.0% from 59.7% to 75.7%. The increased catch of fish below the MRL was minor and far below the regulated limits. Our results demonstrate that a simple T90 codend represents an advantageous alternative to the more complex selection system with a rigid sorting grid currently enforced in the Northeast Atlantic demersal trawl fishery.