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Monitoring the effects of offshore wind farms on the epifauna and demersal fish fauna of soft-bottom sediments

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Abstract:
One year after the construction of 55 monopiles on the Bligh Bank, changes within the softsubstratum epibenthos and fish were observed, both on ecosystem component level and on species level. Analyses were conducted to discriminate between effects of the presence of turbines and effects as a result of changing activities in the vicinity of the wind farms (fringe effects). The results showed a decrease in total demersal fish densities and an increase in epibenthos densities within the wind farm. The changes in demersal fish may have resulted from the absence of fisheries in the area or local changes in sedimentology and infaunal communities. For commercially important flatfish, we observed higher densities (turbot, sole) and/or changes in length-frequency distribution (turbot, plaice). This may signal a refugium effect, but bearing in mind that large flatfish such as sole do not stay within a wind farm for longer periods, this effect will be limited. The increase in epibenthos probably resulted from the presence of hard substrates and their fouling communities and from the absence of fisheries. The increase, however, was mainly seen for dominant, scavenging species such as echinoderms and hermit crabs. Signs of recovery of populations of long lived species vulnerable to trawling were not yet observed in autumn 2011 at the Bligh Bank. Some differences between fringe stations and reference stations were described but they cannot straightforwardly be linked to fringe effects resulting from changing activities in the close vicinity of the wind farm concession.

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