Bottom-trawling along submarine canyons impacts deep sedimentary regimes

Sarah Paradis,Albert Palanques,Pere Masqué,Pere Puig,Jacobo Martín,Xènia Juan-Díaz

doi:10.1038/srep43332

Abstract

Many studies highlight that fish trawling activities cause seafloor erosion, but the assessment of the remobilization of surface sediments and its relocation is still not well documented. These impacts were examined along the flanks and axes of three headless submarine canyons incised on the Barcelona continental margin, where trawling fleets have been operating for decades. Trawled grounds along canyon flanks presented eroded and highly reworked surface sediments resulting from the passage of heavy trawling gear. Sedimentation rates on the upper canyon axes tripled and quadrupled its natural (i.e. pre-industrialization) values after a substantial increase in total horsepower of the operating trawling fleets between 1960 s and 1970 s. These impacts affected the upper canyon reaches next to fishing grounds, where sediment resuspended by trawling can be transported towards the canyon axes. This study highlights that bottom trawling has the capacity to alter natural sedimentary environments by promoting sediment-starved canyon flanks, and by enhancing sedimentation rates along the contiguous axes, independently of canyons’ morphology. Considering the global mechanisation and offshore expansion of bottom trawling fisheries since the mid-20th century, these sedimentary alterations may occur in many trawled canyons worldwide, with further ecological impacts on the trophic status of these non-resilient benthic communities.

Highlights

There is a growing perception based on scientific evidence that we are currently entering a new epoch, the Anthropocene, where human activity has become the main driver of global environmental change[1,2,3]
The Catalan margin is incised by many submarine canyons which hold important bottom trawling fishing grounds in its heads, rims, and flanks (Fig. 1), targeting the blue and red deep-sea shrimp, Aristeus antennatus, whose life-cycle is closely related to these seafloor morphological features[32,33]
Several impacts caused by bottom trawling are evident in the sediment cores collected in the Barcelona continental margin (Fig. 1)

Summary

Introduction

There is a growing perception based on scientific evidence that we are currently entering a new epoch, the Anthropocene, where human activity has become the main driver of global environmental change[1,2,3]. The Catalan margin is incised by many submarine canyons which hold important bottom trawling fishing grounds in its heads, rims, and flanks (Fig. 1), targeting the blue and red deep-sea shrimp, Aristeus antennatus, whose life-cycle is closely related to these seafloor morphological features[32,33]. Canyons in this passive margin act as sediment depocenters of particulate matter directly delivered by rivers or resuspended and advected off-shelf during storms and dense shelf water cascading events[34,35], which is transported along the NW Mediterranean margin by the geostrophic Northern current[36,37]. Given the micro-tidal characteristic of the enclosed Mediterranean Sea, internal waves within submarine canyons are close to the inertial frequency and the associated currents are weak, rendering this process relatively insignificant with respect to the local sediment resuspension mechanisms along these canyons[39,40,42,43]

Methods

Results

Conclusion