MEPS 430:71-86 (2011)  -  DOI: https://doi.org/10.3354/meps09112

ABSTRACT: The loss of emergent epifaunal biomass due to fishing impacts has not been quantified at the scale of an entire fishery. Here, based on an analysis of the impacts of the scallop dredge fleet around the Isle of Man, Irish Sea, we show how fishing and the physical environment act to determine the biomass and size composition of emergent epifauna. The epifauna create habitat structure that is used by juvenile scallops and other species, thus providing an important ecosystem service. Epifauna were identified and quantified based on photographs taken during an extensive survey of the territorial waters of the Isle of Man. On hard substrata, the effect of tidal velocity on total biomass (g m^–2) and the maximum size (g) of the largest organism encountered in each taxon was positive while wave stress and fishing frequency had a negative impact. We used the results to predict the distribution of biomass and maximum size and to quantify the total effects of fishing. Fishing frequency was the most important factor that affected maximum size of the epifauna, resulting in a mean decrease in size of 17% (range 0 to 66%). Total biomass was predominantly affected by wave stress and tidal velocity while fishing caused a mean biomass decrease of 8% (range 0 to 34%), equivalent to 1.8 g wet weight m^–2. The results have implications for management because they provide an assessment of the overall impact of fishing at the scale of an entire fleet and inform the identification of areas where seabed habitats are most vulnerable to fishing.

KEY WORDS: Sessile benthos · Fishing impact · Environmental impact · Photographic survey