A new paper on blue whale response to military sonar

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.

You can read more about this and see the video on the BBC website: http://www.bbc.co.uk/news/science-environment-23115939 

Read the abstract of the paper at the Proceedings of the Royal Society website: http://rspb.royalsocietypublishing.org/content/280/1765/20130657.

And read more about the research group at Cascadia Research http://www.cascadiaresearch.org/socal-BRS.htm

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A paper out on the evolutionary history of cetacean brain and body size

The abstract from this new paper: 

Montgomery, SH, Geisler, JH, McGowen, MR, Fox, C, Marino, L and Gatesy, J. (accepted) The evolutionary history of cetacean brain and body size. Evolution. DOI: 10.1111/evo.12197

"Cetaceans rival primates in brain size relative to body size and include species with the largest brains and biggest bodies to have ever evolved. Cetaceans are remarkably diverse, varying in both phenotypes by several orders of magnitude, with notable differences between the two extant sub-orders, Mysticeti and Odontoceti. We analyzed the evolutionary history of brain and body mass, and relative brain size measured by the encephalization quotient (EQ), using a dataset of extinct and extant taxa to capture temporal variation in the mode and direction of evolution. Our results suggest that cetacean brain and body mass evolved under strong directional trends to increase through time, but decreases in EQ were widespread. Mysticetes have significantly lower EQs than odontocetes due to a shift in brain:body allometry following the divergence of the suborders, caused by rapid increases in body mass in Mysticeti and a period of body mass reduction in Odontoceti. The pattern in Cetacea contrasts with that in Primates, which experienced strong trends to increase brain mass and relative brain size, but not body mass. We discuss what these analyses reveal about the convergent evolution of large brains, and highlight that until recently the most encephalized mammals were odontocetes, not primates."