Development and testing of a species-selective flatfish ottertrawl to reduce cod bycatches

Published source details Madsen N., Tschernij V., Hansen K. & Larsson P.-. (2006) Development and testing of a species-selective flatfish ottertrawl to reduce cod bycatches. Fisheries Research, 78, 298-308.
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This study is summarised as evidence for the following.

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

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

A replicated, controlled study in 1996–1997 in two areas of seabed in the Skagerrak and Baltic Sea around Scandinavia (Madsen et al. 2006) found that modifying the design of a flatfish trawl reduced the unwanted catch of Atlantic cod Gadus morhua, compared to a standard design. Across all trails, total catch numbers of all cod and undersized (<40 cm) cod were reduced in the modified trawl design compared to conventional trawls, by 15–75% in four of four cases, and by 50–80% in three of four cases (the fourth case showed an increase of 24%), respectively. In addition, there were no differences in catch numbers of undersized individuals of the target flatfish species plaice Pleuronectes platessa and flounder Platichthys flesus. However, catches above the minimum landing sizes were higher in modified trawls in one of one plaice (>27 cm: 15%) and one of three flounder (>25 cm: 46%) comparisons. Experimental trials were carried out in June 1996 in the Skagerrak and the North Sea and in December 1996 and January 1997 in the Baltic Sea. Trials compared two modified trawl designs to conventional trawls targeting plaice (Skagerrak/North Sea) and flounder (Baltic Sea). Modifications included a triangle of large mesh (400 mm) at the trawl opening, reduced flotation to keep a low vertical opening, a long headline to increase the seabed area swept by the trawl, and different configurations of square mesh panels/windows (see original paper for full gear specifications).

(Summarised by: Leo Clarke)