Deep-sea crustacean trawling fisheries in Portugal: quantification of effort and assessment of landings per unit effort using a Vessel Monitoring System (VMS)

Juan Bueno-Pardo,Sofia P Ramalho,Marina R Cunha,Ana García-Alegre,Mariana Morgado,Henrique Queiroga,Rui P Vieira

doi:10.1038/srep40795

Abstract

Mapping and quantifying bottom trawling fishing pressure on the seafloor is pivotal to understand its effects on deep-sea benthic habitats. Using data from the Vessel Monitoring System of crustacean trawlers along the Portuguese margin, we have identified the most exploited areas and characterized the most targeted habitats and water depths. We estimated a total trawling effort of 69596, 66766, and 63427 h y−1 for the years 2012, 2013, and 2014 respectively which, considering the total landings estimated for this gear, yield values of 20.76, 21.06, and 19.11 kg of landed fish per trawled hour. The main trawling pressure is exerted in the South and Southwest Portuguese margins, on muddy and muddy-sand bottoms between 200 and 700 m water depths, while in the North and Central-West coasts a minor effort, at shallower waters and across a wider range of habitats, is also applied. The most landed species are crustaceans such as rose shrimp and Norway lobster, although this varies importantly between the different regions of Portugal, being fish and cephalopods the main captures in the Northern ports. We discuss the consequences of trawling for the impacted communities as well as the characteristics of the commercialization of these captures in Portugal.

Highlights

This work aims to provide an accurate mapping of the distribution of trawling effort, as well as new insights into the situation of crustacean trawling in the Portuguese continental margin, with special attention to the quantification of trawling effort imposed in the different deep-sea habitats
During the three years of study, the total area of the Portuguese margin affected by crustacean trawling remained relatively constant, with a total of 12262, 13815, and 11349 km[2] for 2012, 2013 and 2014
This work quantitatively describes the distribution of the trawling effort made by crustacean trawlers and characterizes the most impacted habitats in the Portuguese continental margin using a vessel monitoring system (VMS)

Summary

Introduction

The commercial exploitation of the deep-sea must be monitored and managed with attention to the nature and selectivity of the deployed gears, the vulnerability of the exploited habitats and the biology of both target and non-target species (e.g. many of the deep-sea species have a slow recoverability rate due to their k-selected life history traits such as slow growth and long lifespans)[15,16,17] In this sense, this work aims to provide an accurate mapping of the distribution of trawling effort, as well as new insights into the situation of crustacean trawling in the Portuguese continental margin, with special attention to the quantification of trawling effort imposed in the different deep-sea habitats. We characterize the regional patterns of exploited depths, habitats and species landed, providing an estimation of the landings per unit effort (LPUE) for this métier along the Portuguese margin

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