Release efficiency and selectivity of four different square mesh panel configurations in the Basque mixed bottom trawl fishery

Elsa Cuende,Luis Arregi,Manu Sistiaga,Mikel Basterretxea,Bent Herrmann

doi:10.3989/scimar.04975.17a

Elsa Cuende, Luis Arregi + Show 3 more

Open Access

https://doi.org/10.3989/scimar.04975.17a

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Abstract

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP’s release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries.

Highlights

The landing obligation established under the new Common Fisheries Policy (EU 2013) aims to eliminate the discard of commercial species and represents a big challenge for mixed fisheries with large quantities of discards (de Vos et al 2016)
According to the regulations specified by the European Commission (EC 2006), the vessels participating in this fishery usually use a trawl net with a 70 mm diamond mesh codend combined with a 100 mm square mesh panel (SMP) (2 m long, 1 m wide) inserted in the upper panel of the extension piece of the trawl
This study focused on hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou), which are two common gadoids in the northeast Atlantic and are important species in this fishery (Rochet et al 2014)

Summary

Introduction

The landing obligation established under the new Common Fisheries Policy (EU 2013) aims to eliminate the discard of commercial species and represents a big challenge for mixed fisheries with large quantities of discards (de Vos et al 2016). Recent studies have shown that most undersized individuals that escape the gear do so through the codend rather than through the panel (Nikolic et al 2015, Alzorriz et al 2016). Several studies have investigated the functioning and release efficiency potential of SMPs, but the release efficiency of SMPs has often been estimated to be low due to the low probability of contact of the fish with the panel (Herrmann et al 2014, Alzorriz et al 2016, Brčić et al 2018). Stimulators are designed to trigger fish escape behaviour, but the results obtained so far have shown varying degrees of success Mechanical stimulators have been shown to reduce the retention rate of some juvenile fish species (e.g. Kim and Whang 2010), and in some cases light-based stimulators have been able to induce fish escape behaviour through the escape path (e.g. Hannah et al 2015, Lomeli et al 2018)

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