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
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 430: [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86] 2011 ficult to quantify in a systematic way owing to the difficulty of sampling fauna attached to hard substrata, variation in life-history traits (colonial versus single individuals, senescence of some hydroids in winter), variation in body form with environmental conditions and the absence of precise estimates of the frequency and intensity of fishing impacts (Van Dolah et al. 1987, Henry et al. 2006.Sessile epifaunal species and other habitat-forming organisms are widely distributed on the continental shelf and display a range of life-history traits and morphological characteristics that influence the environments where they are found and their vulnerability to fishing impacts. There is limited information on growth, reproduction, mortality and the ecological requirements of the sessile species that occur in northern European waters (see BIOTIC database, MarLIN website, www.marlin.ac.uk/biotic/). The distribution of these biota is affected by substratum stability, turbidity, nutrient supply, light availability, temperature and hydrodynamical conditions that in turn affect the resilience of the habitat to fishing disturbance (Hall 1994, Jennings et al. 1999, Callaway et al. 2002. A better understanding of the relationships bet...