Abstract
The harbour porpoise (Phocoena phocoena) is the smallest of the whale species that inhabit European waters. Over the recent years it has experienced dramatic population declines in many parts of its range, and it has therefore become increasingly important understanding how fluctuations in its abundance might be linked to various anthropogenic factors. Here we use an individual-based model (Porpoise-POP) to investigate how possible disturbances by wind farms and ship traffic affect the porpoise population in Kattegat. The model simulates both the detailed movement behaviour that has been observed in nature using dead-reckoning instruments, long distance dispersal between areas where porpoises are often observed, and reproductive patterns reported in the literature. Disturbances are simulated by letting virtual porpoises turn away more steeply from objects the more noisy they are. The results do not suggest that the existing wind farms affect the size of the porpoise population and its long-term survival. Construction of new wind-farms at Kriegers Flak and Store Middelgrund is not predicted to affect its dynamics either, whereas the existing ship traffic is likely to cause a reduction in the population size, assuming that porpoises react to noise from ships by turning away. The results suggest that the Kattegat porpoise population is capable of recovering after being reduced to levels far below its potential carrying capacity.