Purpose > Impact of Man Made Noise
Navy Sonar
A subject of considerable interest is whether man-made sounds are directly injuring whales and displacing whales from their otherwise normal habitat.
Whales undoubtedly hear noises made by ships, aircraft, sonar systems, explosives and petroleum exploration activities. Because whales are presumed to habituate to such man-made sounds, it is often difficult to understand the impact of such noise on whales.
mid-frequency sonar on a ship's bow
"The low frequency active (LFA) sonar system (LFA website) can sometimes be heard at levels 20 dB above ambient background noise at a range of 1000 km", thus nearly all baleen whales in an ocean basin can detect such a sonar operating anywhere in the ocean basin if conditions are otherwise quiet.
stranded beaked whale
A series of whale strandings, involving mostly beaked whales have been correlated to operation of Naval mid-frequency sonars. The galvanizing event was that in the Bahamas in 2000 (open window for Bahamas Interim Report). A review article on the problem written by John Hildebrand for the International Whaling Commission is available (open window for Hildebrand Review article ).
Commercial Shipping
Merchant ships are steadily becoming larger, resulting in higher ambient noise levels at low frequencies in the worlds oceans. A recent study off Southern California shows the rate of noise increase to be about 0.3 dB per year in the shipping noise band. An article describes a recent study (open window for J.A.S.A. article abstract) or view the press review in Natural History magazines, November 2006 Samplings column (open window for Natural History Magazine )
The most significant of those measurements are presented here:
If you wish to replot the red curve in Figure 2 of the article as shown below (open data table for Fig. 2)
Figure 2, Change in average ocean ambient noise level off Southern California in deep water.
If you wish to replot the red curve in Figure 3 (open data table for Fig. 3),
Figure 3, Change in February ocean ambient noise level off Southern California in deep water, when blue whales are absent.
If you wish to replot the red curve in Figure 4 (open data table for Fig. 4).
Figure 4. Change in November ocean ambient noise level off Southern California in deep water, when blue whale song is most prominent.