Salmon farm impacts on muddy-sediment megabenthic assemblages on the west coast of Scotland

We assessed the impact of salmon farms on the megabenthos associated with muddy habitats using a novel drop-and-drift video camera approach. Megabenthic burrowers and suspension feeders were adversely affected by farm proximity, as indicated by modelled benthic flux of dry solids (DSFlux, g m(-2) yr(-1)). The burrow-count threshold DSflux was 400, beyond which burrow density declined rapidly. Suspension feeder densities were reduced by a factor of 4 in close proximity (DSFlux > 8000 g m(-2) yr(-1)) to the salmon farms, but only where the sediment was relatively muddy. In terms of suspension feeders, threshold levels of DSFlux varied between sites, ranging from 12 to 665 g m(-2) yr(-1). There was no evidence that vagile predator/scavengers were either attracted to, or repelled by, salmon farms. We conclude that burrowers and suspension feeders were relatively resilient to salmon farms in muddy, sea-loch habitats and that detectable impacts did not exceed 100 m from the cage boundary.