Browsing by Subject "acoustics"

Sound travels faster and further in water than in air while electromagnetic radiation, among it visible light, attenuates fast. Marine animals have adapted to use sound in foraging, predator avoidance, orientation and communication with conspecifics. The underwater soundscape of the Baltic Sea remains largely undiscovered. The area is a unique acoustic environment due to its variant hydrography, broken coastline, shallowness, low salinity and the resulting strong stratifications. The harbor porpoise (Phocoena phocoena) is the only cetacean inhabiting the area, and its Baltic Sea subpopulation is critically endangered. This work is based on first sound pressure measurements of BIAS (Baltic Sea Information on the Acoustic Soundscape) -project by Finnish Environment Institute and other project participants. Measured sound pressure levels are compared to weather and shipping observations to collect information about the contributions of natural and anthropogenic sound sources to underwater sound pressure levels in the Baltic Sea. In addition porpoise observations collected at the Universities of Southern Denmark and Århus are compared to measured sound pressure levels and shipping data to examine if increased noise levels or increased shipping activity have an impact on harbor porpoise echolocation activity. The results show that at the Gulf of Finland both weather and shipping drive the levels of ambient noise at low frequencies (63 and 125 Hz third-octave bands). However the sound pressure levels caused by ships near the stations (up to 5 km) always exceeded all natural variation. Increased sound pressure levels and ship proximity seemed to have an impact on porpoise activity at the area. When a ship was very close (2 km), the registrations of porpoise echolocation clicks decreased with decreasing proximity to ship. On the other hand during spring months an increase in porpoise echolocation was recorded in relation to increased sound pressure levels, which might indicate the porpoises compensating to increased background noise by echolocating more frequently or loudly.