Findings Reveal Sonar Disturbs Blue Whale Feeding·
No one really knows why pods of whales spontaneously drive themselves aground. Military sonar may be one culprit, and the need to train and test submarine tracking technology in open water could put the US Navy in conflict with the gentle cetaceans that feed and pass through military ranges. Although solitary endangered blue whales are rarely victims of sonar stranding, this does not mean that they are unaffected by high intensity sonar. ‘We wanted to understand better what the common behavioural responses are in blue whales when they are exposed to [sonar]’, says Brandon Southall from the University of California, Santa Cruz, USA. So, he and a team of 14 colleagues embarked on a marathon tracking program to investigate the reactions of blue whales to sonar. The team publish their discovery that blue whales stop feeding on deep patches of krill when they encounter sonar in Journal of Experimental Biology.
‘The ocean is a big place and it can be easy to miss and lose even the biggest animals ever on the planet, but, because they are so large and have very tall blows, they are actually among the easiest marine mammals to track’, says Southall. Admitting that being close to one of these incredible animals can be daunting, Southall explains how the scientists manoeuvred close (~5 m) to the colossal animals in a 6 m inflatable boat to attach the suction tags, which record the animals’ depth, movements and sounds in the water. ‘The driver of the small boat is totally critical’, says Southall, adding, ‘we had one of the most experienced people in the world doing this: John Calambokidis from the Cascadia Research Collective’.
Once the tag was attached and six trained observers were in place to confirm the animal’s movements at the surface, the team generated sonar signals from a boat located about 1 km away for 30 min or an hour. During this time, they monitored the animals’ reactions, first as the sonar became louder and then after the noise ceased. In addition, Ari Friedlander and Elliot Hazen used echosounders to track krill—the whales‘ favourite delicacy—when conditions in the vicinity permitted, to get a better idea of when and where the whales were in relation to their dinner.
Photo: Mike Baird/Wikimedia Commons
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