Abstract
The effect of speed through water on the footrope capture efficiency of a survey bottom trawl was experimentally investigated by repetitively towing at three vessel speeds (2.5, 3.0 and 3.5 knots) with an auxiliary net attached underneath the trawl footrope to capture fish escaping beneath the trawl. Length-dependent capture efficiencies were then computed from the number of fish caught in both the trawl and auxiliary net. Capture efficiencies for Pacific cod Gadus macrocephalus, walleye pollock Theragra chalcogramma and Pacific halibut Hippoglossus stenolepis were not affected by fish length or trawl speed. Capture efficiency for skates Bathyraja spp. decreased with increasing trawl speed but was not affected by fish length. Capture efficiencies for arrowtooth flounder Atheresthes stomias and flathead sole Hippoglossoides elassodon increased with fish length and decreased with increasing trawl speed. Our results indicate that in areas of variable current, variation in survey catch per unit effort could be reduced for some species by standardizing towing speed to speed through water or by reducing footrope lift by the addition of sufficient weight to the trawl footrope.
Published Version
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