Reducing discards without reducing profit: free gear choice in a Danish result-based management trial

Published source details Mortensen L.O., Ulrich C., Eliasen S. & Olesen H.J. (2017) Reducing discards without reducing profit: free gear choice in a Danish result-based management trial. ICES Journal of Marine Science, 74, 1469-1479.
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This study is summarised as evidence for the following.

	Action	Category
	Use a topless (coverless) trawl Action Link
	Decrease the circumference or diameter of the codend of a trawl net Action Link
	Fit mesh escape panels/windows to a trawl net Action Link

Use a topless (coverless) trawl

A replicated, controlled study in 2014–2015 in fishing grounds in the North Sea, Skagerrak and Baltic Sea, Northern Europe (Mortensen et al. 2017) found that switching to using a coverless trawl, and various other different trawl gear types/designs, reduced the total discarded catch of seven commercial target species (six fish and one crustacean) compared to conventional trawl types, and the overall effect of using different gear types varied between regions. For one of 12 individual vessels that opted to use a topless trawl (as one of two different gear types used), average total discarded catch of the seven species was lower in the modified trawls (both types combined) compared to the conventional trawl type (modified: 6 kg, conventional: 16 kg). Across all vessels, in two of three regions the average total discarded catch of the seven species was lower in modified trawl types (Skagerrak: 18 kg, Baltic Sea: 256 kg) compared to conventional trawl gears (Skagerrak: 25 kg, Baltic Sea: 328 kg). In the other region (North Sea) discarded catch was higher (modified: 18 kg, conventional: 13 kg). Data were collected from a trial run from December 2014 to July 2015 involving 12 Danish bottom trawlers who were given free choice of trawl gear, in place of the regulatory gear being used, with the challenge of reducing discards. One of the 12 vessels used a 120 mm topless trawl with 1.4–1.6 m vertical opening, as well as a trawl net with a square mesh escape panel (see original paper for other gears types used/vessel). Each vessel switched between using modified and conventional gears between fishing trips.

(Summarised by: Leo Clarke)
Decrease the circumference or diameter of the codend of a trawl net

A replicated, controlled study in 2014–2015 of three fished areas of seabed in the North Sea, Skagerrak and Baltic Sea, Northern Europe (Mortensen et al. 2017) found that choice of modification to bottom trawl gears made by fishers as part of an unrestricted trial, including decreasing codend circumference, increasing mesh size, adding square mesh escape panels and using a coverless trawl, reduced the total discarded catch (fish and invertebrate species) in one of two areas, but not overall, compared to using the regulatory gears. In two of three areas, the average total discarded catch of seven commercial target species (six fish and one invertebrate – see paper for species individual data) was lower for modified trawl gears (Skagerrak: 18 kg/tow, Baltic Sea: 256 kg/tow) compared to the regulated trawls (Skagerrak: 25 kg/tow, Baltic Sea: 328 kg/tow). In the other area (North Sea) average total discard was greater for modified (18 kg/tow) than regulated (13 kg/tow) trawl gears. For all three areas combined, there was no statistical difference in average total discard between modified and regulated trawl gears (modified: 52 kg/tow, regulated: 65 kg/tow). Gear trials were undertaken by twelve Danish bottom trawlers (three to six vessels/area) between December 2015 and July 2015. The fishers were challenged to reduce overall discarding of seven commercial species by modifying or developing new gears and/or changing fishing practice (see original paper for details of all modifications/gears used). Vessels switched between modified and conventional regulatory gears between fishing trips. Data were collected from 421 fishing trips and 2,642 haul deployments.

(Summarised by: Leo Clarke)
Fit mesh escape panels/windows to a trawl net

A replicated, controlled study in 2014–2015 of fishing grounds in the North Sea, Skagerrak and Baltic Sea, northern Europe (Mortensen et al. 2017) found that unrestricted commercial trials of a range of trawl net modifications, including the fitting of mesh escape panels, reduced the proportion of discarded catch (fish and invertebrates) compared to the standard trawl net types. Average discard ratios were reduced by 1–18% for nine of 12 trawlers, four of which tested mesh escape panels (test: 4–474 kg/tow, standard: 8–665 kg/tow); were similar for one vessel using a mesh panel (test: 3kg/tow, standard: 3kg/tow); and were 2% higher (test: 23–46 kg/tow, standard: 5–24 kg/tow) for two vessels that did not test a mesh panel. Twelve trawlers (six in the North Sea and three in each of the Skagerrak and Baltic Sea) were challenged to reduce discards/unwanted catch of fish and invertebrates in a six-month trial of modified (test) and standard/regulated trawl net gears. Vessels had free choice of gear modifications, which included mesh escape panels, changes to the codend circumference, coverless trawls, separator panels and increases in mesh size (see paper for specifications). Vessels were either twin-rig, towing test and standard nets at the same time, or single-rig and switching between test and standard gears between fishing trips.

(Summarised by: Leo Clarke)