Monitoring the effects of offshore windmill parks on the epifauna and demersal fish fauna of soft-bottom sediments: baseline monitoring

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    This chapter reports on the condition of demersal fish, benthopelagic fish and epibenthos in the concession zones and reference zones of the Thorntonbank windmill park in the third year after the installation of the first six turbines, and on the effects of increased fishing effort just outside the Thorntonbank concessions. Due to practical issues following access restrictions in the Belwind
    concession area, no samples could be taken in 2010 of the Bligh Bank impact area. Hence, the data of 2010 on the Bligh Bank and Oosthinder reference zones were stored for future analyses concerning natural temporal variation in the vicinity of the Belwind windmill park. In 2009, some alterations within the epibenthos and fish assemblages were observed in the impact area on the Thorntonbank. These included (1) higher densities of horse mackerel (Trachurus
    trachurus) in autumn 2009 and (2) lower densities of sole (Solea solea) in spring 2009, compared to the reference areas around the Thorntonbank. These observations, however, were not confirmed by the 2010 data. Newly observed differences between the impact area and the reference areas in 2010
    included (1) generally larger individuals of the swimming crab Liocarcinus holsatus and the brown shrimp Crangon crangon at the impact station, which may reflect either increased growth due to a high food availability or increased predation pressure eliminating smaller individuals; (2) higher autumn densities of small whiting Merlangius merlangus at the impact station. The observed increase in fisheries intensity of the Belgian fleet and recreational fisheries in the area north of the concession had little effect on the level of density, biomass and diversity. However, the length-frequency distributions of sole showed an absence of the smallest size classes in both seasons of 2010, which could be the result of increased indirect fishing mortality (such as discards) or of changes in the local benthic community. Similarly, there was a striking reduction in the individuals
    in the size classes ranging between 21 and 26 cm for whiting M. merlangus in spring 2010 at the fringe stations. There were some differences between fringe stations and reference stations for small demersal fish and for epibenthos. Generally, these differences were highest in 2009 and more or less
    normalized by 2010. These differences between the impact station, fringe stations and reference stations may indicate changes in predation pressure, food supply and recruitment. Further monitoring and targeted research actions are needed to confirm causal relationships between these observations and the investigated pressures.
    TaalEngels
    TitelOffshore wind farms in the Belgian part of the North Sea: Selected findings from the baseline and targeted monitoring
    EditorsSteven Degraer, Robin Brabant, Bob Rumes
    Aantal pagina's16
    UitgeverijRoyal Belgian Institute of Natural Sciences
    Datum2011
    Pagina's65-81
    ISBN van geprinte versie978-94-9069-581-1
    StatusGepubliceerd - 2011

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