Effect of the headline height of gillnets on species selectivity in the Gulf of Maine

Abstract

Species selectivity of two types of low height experimental gillnets, 8 mesh deep (MD) and 12 MD, was compared with that of the standard cod gillnet (25 MD) and the tie-down flounder gillnet in inshore waters of the western Gulf of Maine. The experiment was designed to investigate whether using the lower nets could reduce the catch of the Atlantic cod ( Gadus morhua) while maintaining comparable catch of flounders. The results indicate that the 8 MD experimental net caught significantly less cod than the standard cod net ( t-test, P < 0.001), the tie-down flounder net ( t-test, P < 0.05), and the 12 MD experimental net ( P < 0.001). The size of cod caught by the tie-down nets was significantly smaller than those by the 8 MD or 12 MD nets ( P < 0.05). The 8 MD net caught marginally more flounders (combined number of yellowtail flounders, Limanda ferruginea, American plaice, Hippoglossoides platessoides, witch flounder, Glyptocephalus cynoglossus, and winter flounder, Pleuronectes americanus) than the standard cod net ( P = 0.05), but significantly less than the tie-down net ( P < 0.001). There are no significant differences in flounder catch rates between the 8 MD net and the 12 MD net ( P > 0.05). In addition, the tie-down net caught twice as much monkfish, Lophius americanus, sea raven, Hemitripterus americanus, and rock crab, Cancer irroratus, three times more American lobsters, Homarus americanus, and four to eight times more thorny skates, Amblyraja radiata, than the other three types of nets. On the other hand, the standard cod net caught significantly more spiny dogfish, Squalus acanthias, and white hake, Urophycis tenuis, than the other three nets ( P < 0.001). While further experiments are still needed in different fishing areas and seasons, the 8 MD low profile nets have great potential to substitute the standard cod net to maintain flounder catch rates while reducing the catch of cod.