Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance

Abstract

Bottom trawling is the most widespread human activity affecting seabed habitats. Here, we collate all available data for experimental and comparative studies of trawling impacts on whole communities of seabed macroinvertebrates on sedimentary habitats and develop widely applicable methods to estimate depletion and recovery rates of biota after trawling. Depletion of biota and trawl penetration into the seabed are highly correlated. Otter trawls caused the least depletion, removing 6% of biota per pass and penetrating the seabed on average down to 2.4 cm, whereas hydraulic dredges caused the most depletion, removing 41% of biota and penetrating the seabed on average 16.1 cm. Median recovery times posttrawling (from 50 to 95% of unimpacted biomass) ranged between 1.9 and 6.4 y. By accounting for the effects of penetration depth, environmental variation, and uncertainty, the models explained much of the variability of depletion and recovery estimates from single studies. Coupled with large-scale, high-resolution maps of trawling frequency and habitat, our estimates of depletion and recovery rates enable the assessment of trawling impacts on unprecedented spatial scales.

Choosing best practices for managing impacts of trawl fishing on seabed habitats and biota

“…Brief examples and performance‐based analyses are used to develop guidance on best practices for a wide range of fisheries and associated management systems. Building on previous analyses of the impacts and management of trawling activities (Collie et al, ; Hiddink et al, , ; Pitcher et al, ; Sciberras et al, ), we address multiple knowledge gaps identified in a prioritization exercise concerned with reducing the environmental impacts of trawling (Kaiser et al, ). The resulting guidance on best practices is intended to help managers and the industry minimize environmental impacts of trawling per unit weight or value of landed fish, while achieving a sustainable level of fish production.…”

Recovery linked to life history of sessile epifauna following exclusion of towed mobile fishing gear

“…Although they are economically valuable, scallop dredge fisheries have well‐known adverse effects on benthic communities, leading to reductions in diversity and production (Kaiser, Collie, Hall, Jennings, & Poiner, ; Lambert, Jennings, Kaiser, Davies, & Hiddink, ). Nevertheless, the effects of scallop dredging vary considerably according to the environmental context in which scallop dredging occurs, such that some benthic communities exhibit higher resilience to disturbance than others (Hiddink et al., , ). Of particular concern are the effects of dredges (and other towed mobile fishing gears) on stable biogenic habitats, such as reefs, or on longer‐lived fauna.…”

The assessment of fishery status depends on fish habitats

“…Two advances in technology are creating new opportunities for global‐scale synthesis of hard‐to‐observe habitats. First, models based on meta‐analysis of experimental trawling may allow global estimation of the impacts of trawling on soft‐sediment habitats (Hiddink et al., ). Second, video monitoring and automated image analysis are enhancing capacity to observe large areas of habitats, particularly in areas that are difficult to survey with conventional methods (e.g., Ferrari et al., ).…”

“…Few studies have documented impacts of trawl disturbance on soft‐sediment fish habitats, but these effects include both direct long‐term negative impacts of trawling on habitats that improve juvenile survival and positive food subsidies to fish because injured or dying fauna are left in the wake of trawling gear (Collie et al., ). Soft‐sediment regions provide a wide variety of important habitats to numerous fisheries species, but these different habitats vary widely in their resilience to trawl disturbance (Hiddink et al., ). Future modelling studies could combine estimates of biogenic habitat resilience with maps of habitat types to estimate the global impact of trawling on biogenic seabed habitats (Hiddink et al., ).…”

“…Soft‐sediment regions provide a wide variety of important habitats to numerous fisheries species, but these different habitats vary widely in their resilience to trawl disturbance (Hiddink et al., ). Future modelling studies could combine estimates of biogenic habitat resilience with maps of habitat types to estimate the global impact of trawling on biogenic seabed habitats (Hiddink et al., ). This information combined with information on fish habitat associates, like that in our Fishscape database, could be used to assess the degree to which trawling impacts on habitats may have affected fishery status at a global scale.…”