Experimental bottom trawling finds resilience in large-bodied infauna but vulnerability for epifauna and juveniles in the Frisian Front

Abstract

In this study, we analysed the benthic effects of two in situ fisheries disturbance experiments using a combination of side-scan sonar, high definition underwater video, sediment profile imagery, and box core sampling techniques after conventional beam trawling and box core sampling after electric pulse trawling in a southern North Sea habitat. Acoustic and optical methods visualised the morphological changes induced by experimental beam trawling, showing the flattening and homogenisation of surface sediments. Video transects found a 94% decrease in epibenthos in beam trawled sediments compared to an untrawled control site and a 74% decrease in untrawled sediments of the same transect. Box core samples taken 5.5 h, 29 h and 75 h after trawling detected a downward trend in infaunal densities and species richness that continued after the initial impact with small-bodied and juvenile taxa being especially prone to depletion. Data from shallow sediment samples showed trawl resilience in large mud shrimps and evidence of their upward movement towards the sediment surface after disturbance. Both trawl gears induced significant changes to infaunal communities, with no differential effect between the two gears. Our results suggest that in the Frisian Front, trawling may favour the survival of deep burrowers while removing surficial macrofauna.