Sonar from ships or helicopters changes the diving behavior of cuvier’s beaked whales and sturgeons when foraging. U.S. Researchers led by erin falcone of the foundation for marine ecology and telemetry research write in the journal "royal society open science".
They had fitted 16 animals off the southern california coast with transmitters and observed how the whales responded to sonar noise from militaristic exercises.
Thus, all phases of the diving cycles lengthened when the animals were exposed to the sonic pulses. The cuvier’s beaked whales (ziphius cavirostris) stayed longer in the deep dive phase, on average 90 instead of 60 minutes. Scientists suspect that animals at the bottom of the ocean avoid sound waves. Probably due to the extended diving times the animals had to surface a little longer.
The intervals between deep dives, where the whales are foraging, became coarser. This could weaken the animals in the long term, the researchers say. However, the data could not explain why specimens repeatedly stranded in the vicinity of sites where sonar was used. The behavior of the whales, however, shows an adaptation to the technology. Cuvier’s beaked whales are found in all oceans.
While observing the whales’ behavior, the researchers used underwater microphones to record the sounds of two types of sonar used there during regular military exercises: louder sonars from warships and quieter ones immersed in the sea by helicopters. In addition, the research team received the records of sonar use from the military. The study was supported financially by the U.S. Navy.
The animals responded up to a distance of a hundred kilometers from the sonar apparatus, according to the study. However, the reactions decreased with higher distance. On average, the whales reacted more violently to the quieter sonar of the helicopters and also came closer to them. Researchers suspect that whales avoid ships but are surprised by helicopters.
Scientists in germany are also studying the effects of alarm on whales in the north and baltic seas. Andreas ruser, a biophysicist at the hannover veterinary university foundation, is studying in particular the reaction of porpoises, which orient themselves via gehor. His experiments showed that the whales’ hearing deteriorated briefly after sonar exposure above a certain level of sound energy. The phenomenon resembles the impression people have after going to a disco, ruser says.
Whales could generally hear much higher frequencies than humans. Although the ocean is never completely silent, ruser said, loud noises, such as sonars, explosions or seismic surveys, could disturb or injure the animals. For example, the animals either dive or rise because the sound is steamed on the sea floor and on the water surface.
Cuvier whales are the mammals that can dive the longest and deepest. They can stay under water for far more than 100 minutes and dive to a depth of almost 3000 meters in individual cases.
Researchers guess why mass strandings of the animals occur again and again. Sonars emit sound pulses that echo when they strike an object, such as a submarine. The noise apparently led to atypical behavior of the whales. The stranded whales showed symptoms of decompression sickness. This causes gas bubbles to collect in the body, destroying the tissue. This reaction, also known as diver’s disease in humans, is caused by very deep diving or by surfacing too quickly.