Growing ocean trade hard on the ears of marine mammals

Growing ocean trade hard on the ears of marine mammals A recent report in Natural History magazine has found that low-frequency noise from ships in the waters off of Southern California has increased tenfold since the 1960s.
   The magazine cited a study by WhaleAcoustics, which charted low-frequency ship noise from November 2003 to March 2004 and compared it to U.S. Navy studies of low-frequency noise at several sites off the West Coast of North America in the 1960s. The new study found that the noise level had increased 10 decibels at the Southern California site, 'equivalent to the difference between the ambient noise in a library and that in a busy, big-box retail store,' the story said.
   With commercial ships doubling in number and increasing their horsepower and speed, not to mention the number of voyages made, the higher noise levels could be affecting marine animals that communicate over long distances as far as the northeast Pacific, the study said.