THEY are the silent giants of the deep often identified by their dramatic aerial sprays that can be seen for miles. But the graceful giants of our oceans have long been suspected to be affected by sonar sounds bounced off the seabed by vessels detecting marine creatures or submarines.
New research from an international team of scientists at St Andrews and Iceland universities has now shown sonar waves from naval ships can cause whales to stop feeding, flee or go into deep dives.
The study found that, even from a distance, sounds can severely disrupt the behaviour of northern bottlenose whales, which experts say could be responsible for the number of beaching incidents.
Sensors were attached to a dozen whales and deep-ocean acoustic listening devices to study whales’ reactions to military sonar sounds at distances of up to 28km.
The results, published in Proceedings Of The Royal Society B as part of the 3S (Sea Mammals, Sonar, Safety) international research project, showed whales swam away from the noise source and a deep dive.
It also found the beaked whales consistently reacted at low amplitudes of sonar compared to other cetaceans regardless of their distance to the sound source.
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Professor Patrick Miller, of St Andrews University, who led the study, said: “All tagged whales stopped feeding and individuals started swimming away from the exposure site for several hours when a certain sound level was reached, regardless of their proximity to the source – up to 17 miles (28 kilometres) away.
“One of the whales immediately responded by diving to a depth of 1.6 kilometres (almost a mile) that lasted 130 minutes, which, to the best of our knowledge, is the longest dive recorded for this species of whale.
“The data from the listening device indicated a large-scale response by animals in the exposed area.
“We used a sound source that is smaller than a typical operational naval sonar, so the concern is the distances at which animals respond in the wild to real navy sonars may be significantly greater.”
Beaked whales, which include the northern bottlenose whale, are the second largest in numbers from the cetaceans’ family.
Research on the creatures has increased due to their over-representation in unusual mass strandings during naval sonar exercises.
Their extreme diving behaviour and preference for offshore waters, however, means they remain poorly understood.
This lack of scientific knowledge is highlighted by unexplained occurrences of mass strandings of whales, such as those that occurred last summer 2018 in Scotland, Iceland, Ireland and Norway.
Carcasses of 43 beaked whales were also washed ashore in areas such as Outer Hebrides, Islay, Skye, Tiree, Mull and Ulva last autumn. Beaked whales, which can grow to 43ft long, inhabit area frequently used by naval vessels for sonar training and testing.
Studies indicate animals respond less to sonar from distant naval ships compared to experimental sonar sources much closer.
But levels from distant naval ships were so high, the sound received by the mammal was still loud.
Tests were conducted near Jan Mayen, an island north of Iceland, in an area of the Arctic with little noise pollution.
A dozen northern bottlenose whales were tagged with high-resolution data loggers or satellite-linked tags and exposed to sonar sounds in three experiments.
Dr Paul Wensveen, of the University of Iceland, who co-led the project said: “Within the context of what is known about beaked whales, our results suggest the relative pristineness of the environment might be an important factor in how these sensitive animals respond to sonar sounds.
“A lack of frequent or predictable exposures might mean fewer opportunities for the animals to learn that sonar signals pose lower risk when they come from far away.
“The data from the listening device indicated a large-scale response by animals in the exposed area.
“We used a sound source that is smaller than a typical operational naval sonar, so the concern is the distances at which animals respond in the wild to real navy sonars may be significantly greater.”
Researchers discovered the creatures consistently reacted at low amplitudes of sonar compared to other cetaceans, regardless of how far they were from the sound source.
Beaked whales are the second largest family of cetaceans and inhabit areas frequently used for naval sonar training and testing.
Sonar was developed in the 1950s to detect submarines and mass strandings of beaked whales were rare before this point.
Between 1960 and 2004 there were more than 100 mass strandings reported and the species affected related to an increase in sonar pulses.
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