New Afrodite Seminar               

"Effects of underwater human sounds on marine mammals"

Prof. Peter Tyack - University of St. Andrews, Scotland

Campus Savona MA 116 | 11.15 AM | 31.05.2012

ABSTRACT

Effects of underwater human sounds on marine mammals

The physical properties of the ocean favor sound as a distance sense – you can only see a few tens of meters underwater, but sounds carry hundreds of kilometers. Over tens of millions of years, whales and dolphins have evolved sophisticated acoustic means to communicate over long ranges, and to echolocate to find prey and orient.  During the 1970s, about a century after the onset of motorized shipping, a biologist and ocean acoustician started to worry that elevated noise from ships might reduce the range of communication of whales whose populations were already devastated from whaling. Since that time, studies have shown that whales have mechanisms to compensate for noise, but many studies have shown that marine mammals react to human noise, often by avoiding the area. In the last decade, nature has sent us a signal that human sonar sounds pose an unexpected and lethal risk for deep diving toothed whales, called beaked whales.  Beaked whales dive for up to two hours down to 2000 m on one breath, and use a biosonar to feed on squid and fish that live in the deep ocean.  Starting in the 1960s, a strange pattern of strandings started to emerge with 10 or more beaked whales stranding, some with symptoms of decompression,  over a few tens of kilometers in a few hours. These atypical mass strandings coincide with naval sonar exercises. The strength of the correlation suggests that sonar causes strandings, but because it is impossible to reconstruct where the stranded whales were when they started to respond, it is impossible to study what exposure triggered the stranding. I will report on a series of field sound playback experiments designed to safely test what exposures of sound start to disrupt normal foraging behavior of beaked whales. These results have been used in the US to adjust thresholds for safe exposure. Sonar-related strandings continue in Mediterranean and specifically Italian waters, and it is important to establish safe exposure guidelines for planning and conducting sonar exercises.