This study focuses on the behaviour of fish in response to the operation of the wind farm. Wind farms can have either negative or positive effects on fish, for instance by disturbance due to noise or by acting as a refuge because fisheries are banned within the wind farm. An important feature to determine if positive effects might occur is residence time. The longer individual fish spend in the wind farm, the stronger potential benefit of wind farms can be expected. To our knowledge this is the first study on individual behaviour of fish within wind farms. To study the potential effects of wind farms on fish behaviour, we used two approaches: tagging experiments using Peterson disc tags(mark-recapture) and telemetry experiments by following individual fish with small transmitters (VEMCO) in time. We selected two target fish species that are important for fisheries: sole Solea vulgaris as a target species potentially representing fish that use sand habitats and Atlantic cod Gadus morhua as a target species potentially representing fish that use artificial reefs such as the monopile and scour bed habitats in the wind farm. For the tagging experiment, sole was collected with a beam trawl and for the telemetry cod was caught using fising-rods.

The main purpose of this sampling was to study the effects of the OWEZ windpark on the demersal fish community. Because before installation of the windfarm the main fisheries activity in the area was bottom trawling, it is expected that exclusion of fisheries in the wind farm has the largest effect on the demersal fish community. The wind farm and its safety zone could function as a refugium for these species. If the area functions as a refugium this could be the case for a large number of demersal fish species that occur in the Dutch coastal zone. Owing to this a positive effect of the wind farm on the demersal fish community was expected. The fisheries that occurred in the area targeted larger fish, therefore fisheries mortality was higher on the larger fish. By excluding fisheries in the farm it was expected to change the size distribution in the farm and by that the age distribution of the fish populations. A Hydrolab minisonde, attached to the net, was used for continuous CTD measurements.

The main purpose of this sampling was to study the larvae and eggs in the Dutch EEZ, on a monthly basis

The main purpose of this sampling was to study the effects on fish near the monopiles in the OWEZ windpark. A multi-mesh gillnet is used, with six mesh sizes. Each mesh size forms a single panel of 6,7 meters in width. Every mesh-size panel occurs twice in each net, thus a complete net consists of 12 panels and has a length of about 80 meters.

A high resolution sonar (DIDSON) was used to record the fish community in the vicinity of the monopiles. It is a good instrument for estimating the abundance of fish around the piles and to study the behaviour fish around the piles, although from the images of the DIDSON it is not possible to identify all fish species.

The survey applies hydroacoustic techniques to get an estimate of the pelagic fish stock community due to the construction of the Offshore Windfarm Egmond aan Zee (OWEZ). The monitoring program comprehends a baseline study (T0) before the construction of the windfarm, one study period a year after its construction (T1) and a monitoring study 5 years afterwards (T5). Temperature and salinity data were collected using Hydrolab datasondes attached to the towed body as well as separate downcasts. The acoustic instrument used is a SIMRAD EK60 echosounder with 38kHz split-beam transducer.