bok%3A978-3-658-02462-8.pdf?auth66=1398409209_a0514c2b8e531c058ab8b810a0cad74d&ext=

10.1 • Introduction85 10..Fig. 10.1 Typical pelagic fish species: (a) mackerel (scomber scomber), (b) horse mackerel (Trachurus trachurus), (c) herring(Clupea harengus), (d) sprat (Sprattus sprattus) (photo: (a-d) Sven Gust).offshore windfarms on pelagic fish in the existingcontext of fishery and climate change-inducedimpacts must thus address processes on very differenttemporal and spatial scales. This demandsappropriate survey methods.At present, all studies on the impact of offshorewindfarms on pelagic fish are restricted to a narrowsurvey area of a localised windfarm and surroundingreference areas. The same applies for investigationsat the alpha ventus offshore windfarm. Theseinclude surveys on the distribution of pelagic fish inthe alpha ventus windfarm area and the surroundingarea based on hydroacoustic measurements,addressing immediate attraction and repulsion effectsof offshore windfarms. Attraction or repulsionmay result from a set of effects, which include directchanges in the habitat (electromagnetic fields(EMF), noise, structure) and indirect changes (foodand predators). The effect of changes in the foodsupply was addressed as a single effect by analysisof the gut content of pelagic fish in and outside thealpha ventus area.The study was performed over the period fromAugust 2008 to April 2012.The survey covers a periodbefore construction, during construction andduring operation of the windfarm, in different seasons(spring, summer and autumn), and coveringthe succession in occurrence of the pelagic fish speciesin the study area due to their seasonal migrationbehaviour. The study further includes an evaluationof the survey methods, including development ofa stationary measuring system for hydroacousticlong-term monitoring of fish. Such long-termmonitoring should be part of an overarching (crosswindfarm)study on the effects of offshore windfarms,as discussed below.