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.

Keywords: impacts; logistic recovery model; metaanalysis; systematic review; trawling.

Fig. 1.

Maps of the locations of the studies. The higher-resolution maps of the northwest and northeast Atlantic give more detail for two areas with high concentration of studies. The 200-m depth contour is shown in blue.

Fig. 2.

The relationship between the penetration depth P and depletion d of macrofaunal community biomass and numbers caused by a single trawl pass for different trawl gears (means ± SD).

Fig. 3.

The relationship between trawling frequency and total community (A) biomass and (C) numbers. The thicker lines are the fixed effects, and grey lines are the random effects of the individual studies (not all visible, because many studies had small ranges and low trawling frequencies). Recovery time to 0.95K for depleted total community (B) biomass and (D) numerical abundance as a function of estimated r and initial depletion D. In A and B, lines are the median estimate based on the mean d across all gears. In C and D, lines are the median estimates for three different gear types based on the mean gravel content in the areas where studies using these gear types were carried out. The shaded areas indicate the 5–95% uncertainty intervals for estimates.