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Response to noise (SP 1)

Data on behavioural responses to noise

Installing jacket foundations in 2000 at Ormonde Wind Farm, off the coast of Cumbria. Photo: Vattenfall

Simulation results are influenced by the modelled animals’ behavioural reaction to noise as well as the extent of the areas where they are exposed to increased noise levels. The model used by Nabe-Nielsen et al. built on the assumption that porpoises turned away from noisy objects, and that their tendency to turn away was stronger the more noise the animals experienced. The model was calibrated to ensure that the population densities at different distances from simulated wind farms resembled the ones observed around real wind farms.

In order to ensure that the predictions about the effects of noise on the dynamics of the North Sea population are as realistic as possible it is necessary to obtain more knowledge about how individual animals react to noise. Especially the animals’ responses to very high noise levels, such as the ones produced by pile drivers during the construction of wind turbines, may have large consequences for the population. The aim of the project we describe here is to obtain data on the behavioural responses of porpoises to simulated pile-driving noise.

Combining two methods

In order to obtain detailed and precise data on how animals respond to pile driving noise we plan to equip porpoises with high-resolution tracking devises in order to monitor their movements before and after exposure to noise.

Porpoises will be caught both in pound nets along the coasts of the Inner Danish Waters and using floating gill nets on suitable locations, mostly along the shores of Funen and Sealand. Whereas the first approach relies on the coincidental by-catch in commercial fisheries, the second approach is targeted specifically towards porpoises and requires that researchers are permanently present. By combining the two methods it will be easier obtaining the desired sample size of 10-15 animals. The applicants have 15 years’ experience in tagging porpoises and have all necessary permissions from the Danish authorities.

The animals are equipped with Fastloc GPS tags that provide accurate positions approximately every 1.5 minutes, depending on how often the animals surface. They provide detailed movement tracks from a period of up to 7 days. In addition the animals are equipped with a depth sensor, which provides data on a 1-second temporal resolution, and with an Argos satellite tag which allows continued monitoring of the animal movements after the Fastloc tag stops recording positions.. The Fastloc tags detaches from the animals after approximately two weeks, and they are subsequently recovered in order to retrieve the collected data.

Ideally we will be able to capture animals in areas where wind farms are being constructed and monitor their movements as pile driving takes place. Animals caught outside these areas will instead be exposed to noise from a seismic air gun. The small airgun that we plan on using produces peak pressures 20 dB lower than a real pile driver, but with a comparable frequency spectrum. When exposing animals to noise from an air gun at a distance of 500 m it is therefore equivalent to the noise they would receive from pile driving at a distance of approximately 5000 m. The animals equipped with Fastloc tags will allow us to investigate the animals’ responses over several days after they are exposed air gun noise. The animals equipped with D-tags will provide more detailed information on changes in animal foraging behaviour and on how much noise they receive at different distances from the air gun.

Statistical analyses

The data on animal movements will be analysed using a wide range of advanced statistical analyses that take environmental covariates such as substrate composition, water depth etc. into account when evaluating how strongly animals respond to noise. The behavioural reaction patterns obtained this way will be of the type necessary for parameterizing an individual-based population model. The project requires 4 months of field work and 6 months of office work. Concurrently, the data on the relative population densities in different distances from wind farms should be collected in areas here new wind farms are being constructed (Subproject 4).