Shorter trawls improve size selection of northern shrimp

Ólafur Arnar Ingólfsson,Terje Jørgensen

doi:10.1139/cjfas-2018-0443

Ólafur Arnar Ingólfsson, Terje Jørgensen

Open Access

https://doi.org/10.1139/cjfas-2018-0443

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Abstract

Discards of small northern shrimp (Pandalus borealis) are a problem in the Skagerrak northern shrimp trawl fishery. To reduce catches of small shrimp, we studied the effect of trawl belly length on size selectivity in November 2017 and June 2018 onboard 15 and 27 m double-rigged shrimp trawlers. The selectivity of the vessels’ standard trawl was compared with a trawl differing only in the belly length, being 37% shorter. The trawls had 40 mm bottom panels and cod ends of 35 mm mesh sizes. Eleven and 14 hauls were made, respectively, in 2017 aboard the 15 m vessel and in 2018 aboard the 27 m vessel. The trawls fished shrimp above 19 mm carapace length equally, while catch rates of shrimp below 15.5–16 mm carapace length in the shorter trawl were more than halved. The results were consistent between the two vessels. In short, modifying trawl length is a simple design modification that can reduce catches of small shrimp. Bycatch of Norway pout (Trisopterus esmarkii) was slightly reduced in the shorter trawl, unrelated to fish length.

Highlights

A large proportion of global fish discards has been attributed to small-mesh trawl fisheries, including shrimp trawling (Kelleher 2005)
The technical revised regulations concerning the shrimp fishery in Norwegian waters include a rise in the minimum legal size of shrimp from 6 to 7 cm and the option of imposing real-time closures in areas in which undersized shrimp make up 15% or more by number of the catch (Anonymous 2005)
We observed catch losses of 27% of large shrimp and 54% of small shrimp with the shorter trawl

Summary

Introduction

A large proportion of global fish discards has been attributed to small-mesh trawl fisheries, including shrimp trawling (Kelleher 2005) This was largely remedied in the North Atlantic northern shrimp (Pandalus borealis) fisheries by the introduction of the Nordmøre sorting grid designs (Isaksen et al 1992; Madsen and Hansen 2001), which are in use in most northern shrimp fisheries (Halliday and Cooper 1999; Garcia 2007; Aldrin et al 2012; Gullestad et al 2015). The technical revised regulations concerning the shrimp fishery in Norwegian waters include a rise in the minimum legal size of shrimp from 6 to 7 cm (though this was later reduced to 6.5 cm) and the option of imposing real-time closures in areas in which undersized shrimp make up 15% or more by number of the catch (Anonymous 2005)

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