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

Abstract

ABSTRACT: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 im pacts did not exceed 100 m from the cage boundary.

Changes in Benthos Associated with Mussel (Mytilus edulis L.) Farms on the West-Coast of Scotland

“…Inference to all farms within the sampled population was desired and, therefore, mixed modelling was the appropriate statistical framework for data analysis [35]. Assigning ‘Site’ as a random factor meant that direct comparisons between lochs, or sites within lochs, were not appropriate but that site-specific factors not accounted for in the measured co-variables would be accounted for (but not distinguished) in the random term [35].…”

“…Assigning ‘Site’ as a random factor meant that direct comparisons between lochs, or sites within lochs, were not appropriate but that site-specific factors not accounted for in the measured co-variables would be accounted for (but not distinguished) in the random term [35]. The focus of the research reported here is on patterns in response variables as a function of distance from farm, not whether impact-metric differences between farmed and ‘control’ sites were detectable.…”

“…These torches generated spots of lights that were clearly visible on the screen thus providing a datum from which the viewable area could be calculated. The camera was operated such that the light spots remained in approximately the same location giving a viewable area of approximately 1 m 2 [35].…”

“…However, other research (reviewed and tabulated in [24]) has found no significant changes in megabenthos in relation to mussel farms but this may simply reflect the challenges with respect to monitoring megabenthos (i.e. low experimental power [35]). To date there has been no research into the functional relationship between farm-distance and the megabenthos (rather than comparing near-farm and farm-distant stations) or how this varies between sites [24].…”

“…Compared to the macrobenthos much less is known about the impacts of activities, such as aquaculture, on the megabenthos, primarily because this group is logistically difficult to monitor [35]. The loss of living shells from mussel farms (see above) attracts predators and/or scavengers such as crabs and starfish [36], [37] with Inglis [19] reporting starfish densities up to 39 times higher under a mussel farm compared with farm-distant stations.…”