Semi-pelagic self-adjusting otter boards: effects on the catching performance of a demersal trawl

Abstract

In this study, we investigate whether replacing conventional seabed-contacting otter boards with semi-pelagic self-adjusting otter boards (SAO), which have the ability to maintain a given height above the seabed, affects catch efficiency of a demersal fish trawl. Experimental fishing trials, using the alternate haul method, were conducted in the Kattegat and Skagerrak with three otter board configurations using: conventional seabed-contacting otter boards; the SAO set to maintain a target height over the seabed of 1 m; and the SAO set to maintain a target height 5 m. Replacing conventional otter boards with SAO resulted in a loss of catch efficiency for haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and plaice (Hippoglossoides platessoides), while no significant difference was found for cod (Gadus morhua), common dab (Limanda limanda) and lemon sole (Microstomus kitt). When comparing the SAO - 1m and SAO - 5m, it was observed that SAO - 5m resulted in a loss of catch efficiency for haddock and plaice, a minimal reduction for cod and no significant difference for whiting, common dab, and lemon sole.