A new study by researchers in the USA (Cascadia Research, UC Santa Cruz, Duke, NOAA, US Navy) and the UK (Sea Mammal Research Unit and the University of St. Andrews) came out a few weeks ago which looks at the reaction of feeding blue whales to military sonar. This is the first of its kind looking at the response of baleen whales to sonar. This is a controversial issue since there is scientific evidence (and much media coverage) that suggests that sonar disturbs toothed whales (dolphins and beaked whales), damages their hearing, and could lead to disorientation and mass strandings.
In baleen whales, concerns had been expressed that very low-frequency sounds (0-100 Hz, e.g. ship noise) that overlap with baleen whales' low-frequency vocalisations could disturb their communication, modify their behaviour and even damage their hearing. But up until now it was thought that mid-frequency sonar (3000-4000 Hz), being higher than the frequency range of baleen whale vocalisation and hearing, did not cause any disturbance in these larger whales.
This study does not link strandings in baleen whales to sonar but it is a significant contribution to better understanding the impact of sonar on these animals and does show, for the first time, that mid-frequency sonar does disturb blue whale feeding behaviour. This type of disturbance is significant in an animal which has a relatively short (5 months) but very intensive feeding season where whales must take in huge amounts of food to ensure enough energy for their long migrations and for withstanding the winter when food is scarce. Any persistent disturbance in feeding, due to sound pollution, the passing of a ship, or any other cause, could mean a significant loss of food and energy for these endangered animals.
This research was done by attaching tags with a suction cup (DTAGs) to the back of the whale. The tag records all the movements of the whale as it dives, looks for food and feeds, and therefore enables the researchers to build a 3D model of exactly what the whale is doing beneath the surface. There is a great video of this on the BBC website http://www.bbc.co.uk/news/science-environment-23115939. (Also take a look at a previous post on whale diving behaviour from a study by the same group of researchers.)
So, this new study shows overall that sonar did modify blue whale diving behaviour to avoid the sound, which thereby interrupted feeding at depth. The researchers calculated that this disruption in feeding cost one whale 1 metric ton of lost krill, which is a lot of energy lost if the problem is persistent. Interestingly, however, whales that were feeding at the surface were not affected by the sonar, which indicates a complex relationship between whale behaviour and their response to sonar.
This research shows that frequent use of military sonar in feeding grounds could be a significant problem for endangered blue whales.
