ABIDES-3 Cruise, RV García del Cid

Abstract

It aims to study the current sedimentary processes associated with the activity of trawling, which although it has been investigated in coastal environments, very little is known of those occurring in the continental slope, where the benthic ecosystem is more vulnerable to having reduced capacity for recovery The stress that trawling generates on the seabed is dramatic in areas where fishing activity is intense, continuous and wide geographically, as in the continental strip of the northwestern Mediterranean (coast and slope adjacent to the provinces of Barcelona and Girona). Thus, the main objective of this project is to improve the knowledge of the current mechanisms of erosion, transport and sediment accumulation caused by this form of fishing in the continental slope, with the purpose of identifying the impacts caused on the seabed and get to promote corrective measures to guarantee a sustainable fishery. To do this, time series of currents and sediment concentration in suspension will be recorded by anchoring instrumented anchors in the vicinity of fishing grounds. At the same time, hydrographic profiles will be periodically carried out for the identification of nephelide layers in the water column and surface sediments will be obtained during oceanographic campaigns. Sampling will be carried out both in open slope environments and in the interior of submarine canyons, following a strategy based on the footprint of the fishing effort during the last 10 years. Likewise, a detailed study of the habitats and underwater morphology will be carried out in order to evaluate the status (or level of integrity) of the seabed. The study area will focus on the continental margin of the northwestern Mediterranean, where trawling has been practiced for several decades and where the distribution of fishing effort is known in detail. The specific objectives that are intended to be achieved are 1) monitor sediment transport processes inside submarine canyons and identify the contribution of resuspension by trawling to sedimentary flows; 2) identify the hydrographic structure and the temporal evolution of the distribution of nephelide layers in the water column as indicators of resuspension processes by trawling; 3) evaluate the erosion caused by trawling in the surface sediments of the continental slope and establish sedimentary patterns based on the presence or absence of fishing grounds; 4) determine the sedimentation rhythms inside submarine canyons and evaluate the potential formation of preferential zones of anthropic sedimentary accumulation; 5) quantify the role of trawling in the alteration of organic carbon content in the sedimentary record; 6) to determine, through direct visual observations, small-scale morphological changes and alterations in the habitat and deep benthic ecosystems produced by trawling; and 7) identify large-scale morphological changes in areas of fishing grounds in the study area by performing detailed bathymetries, as well as in other areas of intensive trawling of the Spanish margin from the use of existing bathymetric information