Evaluating the efficacy of semi-pelagic trawl gear to harvest demersal fishes in the U.S

This study involved catch comparison sampling and analyses to determine how changing from a conventional trawl rigged with bottom tending doors to a semi-pelagic trawl rigged with midwater doors affect the catch efficiency of demersal fishes in the West Coast groundfish bottom trawl fishery. For both trawl designs, the most abundant species caught by weight were sablefish, Dover sole, shortspine thornyhead, petrale sole, and lingcod. Mean CPUE values for Dover sole, lingcod, and petrale sole were slightly higher in the semi-pelagic trawl, whereas the conventional trawl showed a slightly higher mean CPUE effort value for shortspine thornyhead. However, these results were only trends and not significant. For sablefish, a significant catch result was observed with the semi-pelagic trawl catching significantly more sablefish (a mean CPUE increase of 169.8% [95% CLs: 38.9-327.9]) than the conventional trawl. Trawl door sensors showed the semi-pelagic trawl exhibited a 42.1 m increase in door spread compared to the conventional trawl, while bottom contact sensors showed the midwater trawl doors outfitted on the semi-pelagic trawl fished on average a minimum of 0.8 m above the seafloor; Thus, providing sufficient height for lower-profile epifaunal and infaunal organisms to pass under the door without contact or disturbance. Our research demonstrates that semi-pelagic trawl gear can effectively harvest demersal groundfishes in the West Coast groundfish bottom trawl fishery while significantly reducing trawl-seafloor interactions.