Do Pacific cod (Gadus macrocephalus) and walleye pollock (Theregra chalcogramma) lack a herding response to the doors, bridles, and mudclouds of survey trawls?

Pacific cod and walleye pollock were subjected to herding experiments in which trawl hauls are conducted repeatedly in an area with the bridles varied among three distinct lengths. For the flatfishes in these studies, catch per unit of area swept (cpue) by the trawls increased greatly with increasing bridle length, indicating that flatfish are stimulated to herd into the path of the net by the action of the bridles. In contrast, the cpue of Pacific cod and walleye pollock did not increase significantly with increasing bridle length. This lack of significance indicates that these two species respond only weakly to any herding stimuli produced by the 83–112 Eastern and Poly Nor'eastern trawls used to conduct groundfish trawl surveys in the North Pacific Ocean.