Developing and testing a novel active-selection (ActSel) bycatch reduction device to quickly alternate trawls between capture and release configurations with real-time triggering

Abstract

Bycatch reduction devices (BRDs) allow selective release of unwanted fish (bycatch) during fishing operations, while retaining target fish. Existing BRDs use passive methods, exploiting differences in fish behavior, size, and/or shape to separate bycatch from target species. Recent availability of practical systems transmitting real-time video from trawls to the towing vessel during routine fishing opens the possibility to develop active selection (ActSel) BRDs, devices that allow trawlers to selectively trigger fish release when bycatch species are observed.Development through numerical modeling, scale-model tests, and full-scale, at-sea trials, resulted in an ActSel BRD system that, when triggered, quickly (average 10 s) and reversibly moved a mesh panel between configurations covering a release opening or leading fish out of that opening. A hydrodynamic kite across that selection panel’s leading edge drove it between catch and release positions. Manipulation of control lines by a remotely-controlled electromechanical reel adjusted the kite’s orientation, determining movements of the mesh panel. Results of full-scale testing of this ActSel system under commercial fishing conditions while trawling for Pacific hake (Merluccius productus) showed that ActSel operation effectively and reversibly changed movement of all fish from normal passage toward the codend to moving toward the release opening. While our sea trials occurred in the Pacific hake fishery, the ActSel has applications to other trawl fisheries, particularly fisheries where real-time video systems are used (i.e., Alaska pollock (Gadus chalcogrammus) fishery).