India, Aug. 6 -- Blue whales are going eerily silent, and scientists across the world are concerned. Researchers have raised alarms after noticing a drop in the number of vocalizations from the marine mammals. A team of scientists used underwater hydrophones to record and trace the sounds of marine life to study the impact of human activity on whales, the National Geographic reported. A detailed study published in the PLOS One journal revealed that heat waves have triggered worrying changes over several years. Toxic algae is 'undermining food sources for whales'.

"It caused the most widespread poisoning of marine mammals ever documented. These were hard times for whales," coauthor and Monterey Bay Aquarium Research Institute biological o...