Male blue whales have been singing at a lower pitch in recent decades, and one oceanographer suggests it is linked to growing populations following the elimination of whale hunting. Songs used by blue whales worldwide to warn off predators and attract mates have become increasingly deeper in tone and are now about 30 percent lower than during the 1960s, says John Hildebrand, a marine biologist at the Scripps Institution of Oceanography. The reason, he believes, is that whale populations have grown significantly since hunting was banned in 1966, and male blue whales now feel less urgency to sing in a high pitch, which they may have been using to communicate with widely scattered females when populations were low. Essentially, when blue whale numbers dropped to just a few thousand during the 1960s, he said, there was a “push to have the sound go to higher frequency so that more of the girls can hear it.” With whale numbers restored, he said, 
male whales have shifted to deeper tones to attract females. Richard Ellis, a whale expert at the Museum of Natural History in New York, was skeptical of Hildebrand’s conclusion, saying, “It’s a great anthropomorphism to suggest that the whales have thought this through.” Meanwhile, a new report from the United Nations Environment Program (UNEP) says large-scale fishing with nets threatens 86 percent of the world’s toothed whales, including dolphins and porpoises.
NOAA