Spatio-temporal trends of the bottom trawling activity in a mud volcano field of the north-eastern Gulf of Cádiz (south-western Iberian Peninsula)

Abstract

Multi-species bottom trawl fisheries are one of the human activities with a great impact on the benthic habitats and their associated biota. This study provides estimates of the bottom trawling activity (effort), catches and landings of the main commercial species as well as an estimation of the total revenue (TR) generated inside a mud volcano field located in the Spanish margin of the Gulf of Cádiz, during a time series from 2007 to 2012. To date, no studies have been carried out to analyse the temporal evolution of bottom trawling activity and TR in a mud volcano fied, or the economic consequences of possible potential bottom trawling regulation of certain sectors harbouring vulnerable and/or threatened habitats. In this study, Vessel Monitoring System data, logbooks and sales slips were used. The spatial distribution of the bottom trawling activity, catches and TR were related to the seafloor morphology and specific bottom types of the mud volcano field. During the time series, a high bottom trawling activity and associated catches was detected in flat sandy and muddy bottoms, including the Anastasya sector and between the Guadalquivir and Cádiz Diapiric Ridges. Low bottom trawling activity and catches were detected in the deepest areas but also in areas with hard and detritic bottoms such as Gazul and Chica sectors as well as in the Diapiric Ridges. A similar spatial pattern was detected for the TR asociated with these bottom trawling fisheries. An increase in bottom trawling activity was detected during the time series, mainly at the end, probably for increasing the TR and mantaining the economic profit due to the instability and increases in fuel prices and offset the increased costs. Based on the obtained information, bottom trawling regulations should be implemented in certain sectors harboring singular and/or threatened habitats and species. In some of these sectors, a low TR from bottom trawling was detected and, bottom trawling regulation may potentially have a low socioeconomic impact. This specific bottom trawling regulation could provide a sustainable balance between bottom trawling activities and habitat conservation in this mud volcano field according to the aims of the Habitats Directive (92/43/EEC) and the European Marine Strategy Framework Directive (2008/56/EEC).