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

Published source details Hannah R.W., Jones S.A., Lomeli M.J.M. & Wakefield W.W. (2011) Trawl net modifications to reduce the bycatch of eulachon (Thaleichthys pacificus) in the ocean shrimp (Pandalus jordani) fishery. Fisheries Research, 110, 277-282.
Share Tweet Email

Actions

This study is summarised as evidence for the following.

	Action	Category
	Modify the design or configuration of trawl gear (mixed measures) Action Link
	Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water) Action Link

Modify the design or configuration of trawl gear (mixed measures)

A replicated, paired, controlled study in 2010 in an area of seabed in the North Pacific Ocean, off Oregon, USA (Hannah et al. 2011) found that modifications to the footrope of prawn trawl gear reduced the capture of unwanted eulachon Thaleichthys pacificus, and other unwanted finfish species, compared to a conventional trawl design. The average weight of unwanted catch was reduced in the modified trawl compared to the conventional trawl, by 34% for eulachon (modified: 1,891, standard: 2,858 g/haul), by 96% for slender sole Lyopsetta exilis (modified: <1, standard: 4 kg/haul), by 97% for other small flatfish (modified: <1, standard: 2 kg/haul) and by 80% for darkblotched rockfish Sebastes crameri (modified: 13, standard: 61 g/haul). However, there were no differences between gear types for whitebait smelt Allosmerus elongatus (modified: 18, standard: 29 g/haul) and Pacific herring Clupea pallasii (modified: 1, standard: 1 kg/haul). In addition, target ocean shrimp Pandalus jordani catches were not statistically different between gear types (see paper for data). Experimental trials were conducted from 26 paired deployments on a double-rigged shrimp trawler in June 2010 (99–148 m depth, 1.6–1.8 knots, 45–60 min). Two trawl types were tested simultaneously: a modified trawl with the central section of the groundline removed and drop chains attached to the central section to help stabilise it, and a standard trawl with a complete groundline (see original paper for gear specifications). Both trawl types had a rigid size-sorting escape grid (19 mm bar spacing).

(Summarised by: Chris Barrett)
Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

A replicated, paired, controlled study in 2010 of an area of seabed in the North Pacific Ocean off Newport, Oregon, USA (Hannah et al. 2011) found that using a different configuration of size-sorting escape grid (decreased bar spacing) in a shrimp trawl net reduced the unwanted catch of eulachon Thaleichthys pacificus (focus species) and of three of five other fish species/groups. Catch rates with a grid of narrower 19 mm bar spacing were lower compared to a standard 25 mm grid, for eulachon (narrow: 319.2 kg/haul, standard: 382.5 kg/haul), slender sole Lyopsetta exilis (narrow: 0.4 kg/haul, standard: 0.6 kg/haul), other small flatfish (species not reported) (narrow: 0.1 kg/haul, standard: 0.5 kg/haul) and darkblotched rockfish Sebastes crameri (narrow: 21.2 kg/haul, standard: 89.2 kg/haul). Catch rates of whitebait smelt Allosmerus elongatus (narrow: 54.7 kg/haul, standard: 50.1 kg/haul) and juvenile Pacific hake Merluccius productus (narrow: 17.7 kg/haul, standard: 16.3 kg/haul) were similar between grids. Catches of the commercial target ocean shrimp Pandalus jordani were similar (narrow: 46.0 kg/haul, standard: 45.5 kg/haul). Data were collected in August–September 2010 from 30 paired deployments (45–60 min) on a shrimp trawler using a double-rigged net. Both sides of the net were identical and had a rigid grid. One side had 19 mm grid bar spacing and the other a standard 25 mm bar spacing, alternated every two hauls (see original paper for gear specifications). Catches from each net were sorted and weighed by species.

(Summarised by: Chris Barrett)