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Population density (SP 4)

Data on local population densities data near wind farms

Harbor porpoises. Photo: Zolvin Zankl. SAMBAH-project

As the animals’ behavioural response to noise is a key element in the simulation model, it is essential to get data on the population densities at different distances from wind-farms under construction (based on passive acoustic monitoring using C-PODs). This type of data can be used for an inverse parameterisation of the model if it proves impossible to obtain enough data on the animals’ direct response to noise (Sub-project 1). If the model is parameterized using the movement data directly, it can instead be used for an independent validation of the model output.

In these simulations the population dynamics were influenced by the effects of noise on animal behaviour as well as the size and location of the areas where animals were exposed to noise. Animals that were scared by noisy objects spent less time foraging, which affected their fitness and ultimately also the dynamics of the population. When re-parameterizing the model for porpoises in the North Sea the fine-scale movements and reactions to noise will be based on data collected with high-resolution GPS loggers. After incorporating the fine-scale movements in the simulation model it is in principle able to simulate realistic porpoise densities in different distances from wind turbines.

Validation of model results

In order to validate that our simulation model produces realistic porpoise densities it is necessary to measure the local population densities in different distances from a site where a wind farm is being constructed. This can be done using passive acoustic monitoring. The most detailed similar study from the North Sea used a setup that that did not allow very precise measures of the effect of the distance from the pile driving area, partly due to a low number of sampling stations. The aim of the project we propose here is to describe such changes in local population densities before, during and after the construction of a wind farm using passive acoustic monitoring.

Passive acoustic monitoring data will be collected using C-Pods by the DanTysk wind farm in the German Bight before, during and after the wind farm is constructed. In the present project description we assume that data are collected by a company with local experience in procuring this kind of data, such as BioConsultSH GMBH, but that DCE/Aarhus University is responsible for developing the experimental design, analysing the data and publishing the results.

Measuring stations

In order to evaluate how porpoise densities decline with distance to the wind farm construction site we suggest using a stratified random design. As the population densities are relatively high in the area we would, based on experience from other studies, expect that 12 measuring stations are sufficient to observe a significant effect of distance to the pile driving area and to obtain relatively narrow confidence bands for the population sizes. We suggest using a design where stations are placed in three arrays pointing away from the wind farm, in the distances 750, 1500, 3000 and 6000 m from the edge of the wind farm. Each station shall include a C-Pod and a noise logger in order to couple the variations in porpoise densities directly to the noise level. Noise loggers only have to be present on stations while pile driving takes place

In addition to the new stations placed in arrays by the wind farm we will use the existing data from the nearby measuring stations DT1 and DT2 in order to estimate long-term trends in the local population density. These estimates will be taken into account when assessing the effects of wind farm construction on the porpoise density in the area.