Predictive models for codend size selectivity for four commercially important species in the Mediterranean bottom trawl fishery in spring and summer: Effects of codend type and catch size.

Jure Brčić,Antonello Sala,Bent Herrmann,Carrie A Holt

doi:10.1371/journal.pone.0206044

Jure Brčić, Antonello Sala + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0206044

Copy DOI

Abstract

Models to predict codend size selectivity for four major commercial species—European hake (Merluccius merluccius), Norway lobster (Nephrops norvegicus), deep-water rose shrimp (Parapenaeus longirostris), and Atlantic horse mackerel (Trachurus trachurus)–in Mediterranean bottom trawl fisheries were established based on data collected during fishing trials using the two legal codends: a 40 mm square-mesh codend and a 50 mm diamond-mesh codend. The models were applied to predict the extent to which size selection depend on codend type, also accounting for the potential effect of codend catch size and fishing season. The size selectivity of the two codends was evaluated and compared in identical simulated controlled conditions. Mesh type significantly affected the size selection of Norway lobster alone, with a slightly better performance of the 40 mm square-mesh codend. A high risk of retention of undersized individuals was predicted for both codends for all species except Norway lobster.

Highlights

The European Commission has identified high levels of discarding as a major structural weakness of the previous Common Fisheries Policy (CFP) [1]
Based on the above considerations, the objective of this study was to establish predictive models for codend size selection of the two legal codends for four major commercial species that are going to be subject to the landing obligation in Mediterranean bottom trawl fisheries —European hake (Merluccius merluccius), Norway lobster (Nephrops norvegicus), deep-water rose shrimp (Parapenaeus longirostris), and Atlantic horse mackerel (Trachurus trachurus)— taking into account the effect of codend catch size and fishing season
All four species have an Minimum Conservation Reference Size (MCRS) defined by Council Regulation (EC) No 1967/ 2006 and are subject to the landing obligation

Summary

Introduction

The European Commission has identified high levels of discarding as a major structural weakness of the previous Common Fisheries Policy (CFP) [1]. The new CFP aims to reduce this wasteful practice [2]. In the Mediterranean region, discards have been increasing in the past 70 years [3] and account for 18.6% of the total catch; bottom trawls are responsible for the bulk of discards [4]. Several measures have been devised to reduce bottom trawl discarding in the EU, among them technological modifications that improve gear selectivity through changes in codend mesh size and/or geometry [5,6,7,8].

Objectives

Methods

Results

Conclusion