Species selectivity in different sized topless trawl designs: Does size matter?

Published source details Krag L.A., Herrmann B., Karlsen J.D. & Mieske B. (2015) Species selectivity in different sized topless trawl designs: Does size matter?. Fisheries Research, 172, 243-249.
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This study is summarised as evidence for the following.

	Action	Category
	Use a topless (coverless) trawl Action Link

Use a topless (coverless) trawl

A replicated, paired, controlled study (year not stated) of multiple fished areas of seabed in the North Sea off Norway and Sweden (Krag et al. 2015) found that use of topless bottom trawls (two designs) reduced the catches of unwanted larger haddock Melanogrammus aeglefinus and of unwanted larger cod Gadus morhua in one of two cases, compared to standard trawls. Total catch numbers of haddock were lower in both large and small topless trawl designs compared to standard trawls (topless: 20–352 fish, standard: 662–2,467 fish). Catches of cod were lower in a larger, high headline topless trawl (topless: 583, standard: 1,755/trawl) but similar in the smaller trawl with low headline (topless: 941, standard: 1,305/trawl) compared to standard trawls. For both species, the effect was significant only for larger individuals (haddock >19–23 cm and cod >34 cm length). Numbers of commercial target Norway lobster Nephrops norvegicus were similar between trawl types (topless: 1,666–1,681 individuals, standard: 1,702–2,057 individuals). Data were collected from 51 comparative trawl deployments in two trials on different commercial vessels (one large, one small), both fishing a topless trawl towed parallel to a similar-size standard trawl. One trial tested a small topless trawl with the upper wings removed and the head rope cut 6.4 m back, and the other a larger topless trawl with the head rope cut 11.3 m back (see paper for full specifications). Catches in each codend were sorted by species and fish lengths measured. Hauls with fewer than 10 individuals of a species were not included for analysis. Study year was not reported.

(Summarised by: Natasha Taylor)