This report describes data collected in 2004 on the harbour porpoise monitoring program in connection to Nysted Offshore Wind farm and compares with results from previous years of monitoring. The year 2004 was the first year of operation of the wind farm and as the monitoring continues throughout 2005, conclusions must be considered preliminary. Conclusions on animal abundance and behaviour during 2004 were nevertheless clear. No significant increase in abundance of porpoises in the wind farm area was seen in 2004 relative to the construction period and levels are still about a factor 5 lower than during baseline monitoring. In parallel with this was a decline observed in the reference area, about 10 km east of the wind farm, but this decline in abundance in the reference area was significantly smaller than in the wind farm itself.
Porpoises were not absent from the wind farm however, and when present their acoustic behaviour was not significantly different from baseline behaviour. The reason why fewer porpoises frequented the wind farm during its first year of operation is unknown and it is too early to establish whether the effect is permanent or recovery to baseline levels is slower than originally anticipated.