Selectivity of large mesh trawl codends in the Gulf of Maine: I. Comparison of square and diamond mesh

Selectivity properties of five codend types were evaluated using the covered codend method. The codends tested were 152, 165 and 178 mm diamond mesh codends, and 165 and 178 mm square mesh codends. A new hydrodynamic codend cover, which was expanded by 12 water-borne kites, was developed, tested and used during the codend mesh selectivity studies. Eighty-six successful tows were completed for the five codends. This paper describes results for two species of roundfish – Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) and four species of flounders – American plaice (Hippoglossoides platessoides), yellowtail flounder (Limanda ferruginea), witch flounder (Glyptocephalus cynoglossus) and winter flounder (Pseudopleuronectes americanus). The results indicate that larger codend mesh sizes retained larger fish for all species for both diamond and square mesh codends. The mesh shape (diamond or square) has no significant effect on the 50% retention length (L50) for roundfish (P > 0.1) while the square mesh codends have significantly smaller L50s for flounders (P < 0.001). The square mesh codend has a narrower selection range (SR) than the corresponding diamond mesh codend for both cod and haddock.