Observation of species living on the bottem of the North Sea.Field survey on macrobenthos communities February 2011vessel: RV PELAGIA (NIOZ, TEXEL)sampling stations: 16 stations in OWEZ and 8 stations in each of the 6 reference areas R1, R2, R3, R4, R5, R6sampling design: 1 boxcore per stationsampling gear: NIOZ boxcorer, sampling depth 20 cm, sampling diameter 30 cmsorting procedure lab:nested sieves 11.2 mm, 6.7 mm, 2 mm, and 1 mm; identification species:macrofauna identified to species level under a stereomicroscope;polychaetes, crustaceans, molluscs and echinoderms identified to species level;juveniles and damaged animals, if unidentifiable, identified at higher taxonomic level (usually the genus); anthozoans, phoronids, oligocheates, nemerteans and turbellaria identified on their taxon level;further procedures:all individuals counted; Individual lengths (mm) of molluscs and echinoids measured;blotted wet weights of polychaetes, larger crustaceans, and ophiuroids measured to the nearest mg; remaining taxa determined per species/group. Small crustaceans (amphipods and cumaceans) only counted.

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.

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 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.

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.