Surface selection of haddock and cod in the Norwegian demersal seine fisheries

Ólafur Arnar Ingólfsson,Svein Løkkeborg,Odd-Børre Humborstad,Finbarr O'Neil

doi:10.1093/icesjms/fsab055

Ólafur Arnar Ingólfsson, Svein Løkkeborg + Show 2 more

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https://doi.org/10.1093/icesjms/fsab055

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Abstract

Abstract Size selection in active fishing gears is a continuous process and undersized fish may escape during the whole fishing operation. Fish that escape during the surface hauling operation are likely to experience higher mortality due to barotrauma-related stress than fish escaping at the fishing depth during the towing process. A well-functioning selectivity device should therefore select mostly at depth for enhancing survival probabilities of escaping fish. The current gear regulation in the Norwegian demersal seine fishery is likely to cause large proportion of undersized fish to escape at the surface. In this study, we estimated surface selection of haddock and cod in demersal seine by using an automatic release system and a small meshed codend that collected fish escaping during surface hauling. The collecting bag contained 19% undersized haddock compared to 10% in the conventional square-mesh codend indicating that about 50% of undersized haddock brought to the surface were released. The proportions of undersized cod were 8% for the collecting bag and 1% for the conventional square-mesh codend. These results demonstrate that surface selection is significant for both haddock and cod. Based on this finding, we discuss methods to improve size selectivity at the fishing depth.

Highlights

Demersal seining is a fishing method used in commercial fisheries around the world
Haddock was measured from all hauls and cod from eight control and eight test hauls
One haul had more than 15% haddock below minimum landing size (MLS) (2.5–19.4%, x 1⁄4 9.7%)

Summary

Introduction

Demersal seining is a fishing method used in commercial fisheries around the world. In Norway, demersal seine is mainly used to target cod (Gadus morhua), saithe (Pollacius virens), and haddock (Melanogrammus aeglefinus). The prerequisite for a well-functioning selectivity device is that escaping fish are alive, vital, and with minimum and only reversible injuries and physiological stress that may affect long-term behaviour, survival, or fitness. Minimizing the cumulative stressors (Breen et al, 2020) encountered during the capture and escape process is vital. Demersal seining and trawling are continuous fishing operations where fish have been observed to escape during the entire process until the codend is taken onboard the fishing vessel (Isaksen and Løkkeborg, 1993; Grimaldo et al, 2009; Herrmann et al, 2013b ). Contrary to fish escaping during towing, those escaping at the surface are likely to experience more severe stressors due to barotrauma, physiological trauma, and physical injury (Davis, 2002)

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