The northeast US fishing industry and other stakeholders have considerable interest in the quality of bottom trawl survey results because of their importance in the setting of quotas, especially those directly derived from bottom trawl indices measured in catch per area swept by the survey net. Net spread (also referred to as wing spread) impacts catches and thus indices and, for the federal northeast bottom trawl survey, it is correlated with the depth at which a tow is performed. As part of an ongoing partnership between the Northeast Fisheries Science Center, the New England and Mid-Atlantic Fisheries Management Councils, members of the fishing industry, and academics in the region, an experiment to evaluate the impact of wing spread on the catchability of a number of species was conducted in the Fall of 2019 on the F/V Karen Elizabeth. The experiment targeted four species of flatfishes using a twin trawl rigging to collect simultaneous observations of catch and wing spread relative to a controlled optimal net spread. We analyzed these data to estimate the effect of net spread on relative catch efficiency and to evaluate the hypothesis that relative catch efficiency decreases as net spread departs from the optimal configuration. We found that, while the total catch was impacted by net wing spread (catches increased with increasing swept-area), there was no evidence of a wing spread effect on relative catch efficiency for any of the flatfish species. These results suggest that bottom trawl surveys should account for swept-area of individual tows, but that it is not necessary to incorporate species- or length-specific efficiency conversions based on the width of the net.

美国东北部渔业和其他利益相关者对底拖网调查结果的质量有相当大的兴趣，因为它们在设定配额方面很重要，特别是直接从底拖网指数中得出的，这些指数以调查网扫过的每面积渔获量来衡量。净散布（也称为翼散布）影响渔获量，从而影响指数，对于联邦东北底拖网调查，它与执行拖曳的深度相关。作为东北渔业科学中心、新英格兰和中大西洋渔业管理委员会、渔业成员和该地区学术界之间持续合作的一部分，一项评估翼展对捕捞能力影响的实验物种数量是在 2019 年秋季进行的F/V 凯伦·伊丽莎白. 该实验针对四种比目鱼，使用双拖网索具收集相对于受控最佳网幅的捕捞量和翼展的同时观察结果。我们分析了这些数据以估计净价差对相对捕捞效率的影响，并评估当净价差偏离最佳配置时相对捕捞效率降低的假设。我们发现，虽然总渔获量受到净翼展的影响（渔获量随着扫掠面积的增加而增加），但没有证据表明翼展对任何比目鱼物种的相对捕捞效率有影响。这些结果表明底拖网调查应考虑单个拖网的扫掠面积，但没有必要根据网的宽度纳入特定物种或特定长度的效率转换。