Recent changes on sediment accumulation rates within submarine canyons caused by bottom trawling activities

Abstract

The offshore displacement of commercial bottom trawling has raised concerns about the impact of this fishing practice on the deep seafloor. This study focuses on the analysis of sediment accumulation rates from sediment cores collected along the axes of La Fonera (Palamós), Arenys, Besòs and Foix submarine canyons, distributed along the Catalan margin (northwestern Mediterranean), where an intensive bottom trawl fishery has been active during several decades. 210Pb chronology, occasionally supported by 137Cs dating, indicates a rapid increase of sediment accumulation rates since the 1970s, in coincidence with a strong impulse in the industrialization of the trawling fleets of this region. Such increase has been associated to the enhanced delivery of sediment resuspended by trawlers towards the canyon¿s interior and to the rapid technical development at that time, in terms of engine power and gear size. This change has been observed in La Fonera Canyon at depths greater than 1700 m, while in the other canyons it is restricted to shallower regions (~1000 m in depth) closer to fishing grounds. Two sampling sites from La Fonera and Foix submarine canyons that exhibited high sediment accumulation rates (0.6¿0.7 cm/y) were reoccupied several years after the first chronological analyses. These two new cores reveal a second and more rapid increase of sediment accumulation rates in both canyons occurring circa 2002 and accounting for almost 2 cm/y. This second change at the beginning of the XXI century has been attributed to a preferential displacement of the trawling fleet towards fishing grounds surrounding submarine canyons (targeting the priced blue and red deep-sea shrimp Aristeus antennatus) and also to technical improvements in trawling vessels, presumably related to subsidies and aids provided by the European Commission to the fishing industry