Trawl net modifications to reduce the bycatch of eulachon ( Thaleichthys pacificus) in the ocean shrimp ( Pandalus jordani) fishery

Abstract

Two trawl gear modifications for reducing fish bycatch (weight) in ocean shrimp ( Pandalus jordani) trawls were tested in June and August–September 2010. The primary focus of the study was evaluating trawl system modifications for reducing bycatch of eulachon ( Thaleichthys pacificus) below levels already achieved via mandatory use of bycatch reduction devices (BRDs). An experimental footrope, modified by removing the central one third of the trawl groundline, reduced eulachon bycatch by 33.9%. It also reduced bycatch of slender sole ( Lyopsetta exilis), other small flatfishes and juvenile darkblotched rockfish ( Sebastes crameri) by 80% or more, but had no effect on bycatch of whitebait smelt ( Allosmerus elongatus) or Pacific herring ( Clupea pallasii). The experimental groundline also reduced the catch of ocean shrimp (weight) by 22.2% in hauls yielding commercial quantities of shrimp (>194 kg/haul) and by 23.2% in all hauls. Reducing bar spacing in a rigid-grate BRD from 25.4 mm to 19.1 mm reduced eulachon bycatch by 16.6%, with no reduction in ocean shrimp catch. It also reduced bycatch of slender sole, other small flatfish and juvenile darkblotched rockfish by 36.8%, 71.8% and 76.3%, respectively with no effect on bycatch of whitebait smelt or young-of-the-year (YOY) Pacific hake ( Merluccius productus). Although both trawl modifications reduced eulachon bycatch, the footrope modification tested, if developed further, has the potential to also avoid trawl entrainment for some demersal fishes, as well as reduce bottom impacts from trawling.