Recent advances in understanding the environmental footprint of trawling on the seabed

Abstract

Bottom trawling accounts for nearly a quarter of wild-capture seafood production, but it is associated with physical disturbance of the seabed leading to changes in benthic abundance, habitat structure, and biogeochemical processes. Understanding the processes of benthic depletion and recovery in relation to different types of fishing gears, and in different seabed types, is an important pre-requisite to inform appropriate management measures to limit or reduce the effects of trawling on the seabed. The combined approaches of meta-analysis and modelling that link fishing-gear penetration of the seabed to benthic depletion, and recovery to taxon longevity, have enabled the development of a modelling framework to estimate relative benthic status in areas subject to trawling. Such estimations are highly sensitive to the spatial resolution at which fishing footprint (trawl track) data are aggregated, and this leads to overinflated estimates of fishing impacts on benthos when coarse-level aggregation is applied. These approaches present a framework into which other “sustainability” criteria can be added, e.g., the consideration of carbon footprints of fishing activities.

Mitigating seafloor disturbance of bottom trawl fisheries for North Sea sole Solea solea by replacing mechanical with electrical stimulation

“…This study applied, and extended, the mechanistic approach to assessing the physical impact of bottom trawling on the sea floor and the benthic community [ 33 , 34 ]. This approach integrates quantitative information on the distribution of the trawling activities and the sea floor habitats [ 1 , 2 ], fishing gear dimensions [ 35 , 40 ] and the sensitivity of the benthic community [ 36 , 37 ].…”

“…In this study, we investigate whether a transition from traditional beam trawling to pulse trawling can reduce the physical disturbance of the seafloor. We focus on the consequences of mechanical disturbance and apply a recently developed impact assessment framework [14,[32][33][34] to estimate fishing footprints (areal extent) and trawling impact indicators, based on the distribution of the fishery and the dimensions of the fishing gears [2,35] and the sensitivity of the benthic community [36,37]. In addition to indicators for precautionary impact (L1), median longevity of the community (L2), and community biomass (PD), we estimate the amount of fine sediments mobilised in the turbulent wake of the fishing gears.…”

A model approach to estimate the hydrodynamic drag and sediment mobilisation applied to tickler chain beam trawls and pulse beam trawls used in the North Sea fishery for sole

“…Chain-mat data enquiry focused exclusively on the southern region where chain-mat beam trawls are more frequently used than in the middle and northern region (Rijnsdorp et al, 2008). The enquiry data was complemented with data obtained from the literature (Fonteyne and Polet 1992;Lindeboom and de Groot, 1998;van Marlen et al 2014;de Groot and Lindeboom, 1994) and from experiments on the impact of flatfish trawls on the seabed (Depestele et al, 2016;2019) and the European wide gear inventory (Eigaard et al, 2016…”

“…Chain matrices were deployed in front of the gear to prevent large stones entering the net (Polet and Depestele, 2010). The use of tickler chains and chain mats has raised concerns about the ecological impact of the beam trawl fishery (Jennings and Kaiser, 1998;Kaiser, 2019). Tickler chains disturb the top layer of the sediment, and may inflict mortality among the benthic invertebrate species Hiddink et al, 2017;Sciberras et al, 2018).…”

Experimentally addressing and evaluating the impact of human activities on marine organisms

“…They also provide a case study that highlights and discusses challenges in interpreting meta-analyses (data synthesis approaches) on the thermal limits of fishes. Finally, Kaiser (2019) illustrates the use (and pitfalls) of meta-analysis and modelling in the development of estimates of relative benthic status (RBS) after seabed disturbance by bottom trawling, and how the impact of other human-related activities on marine populations could be informed by similar approaches.…”