Mid Frequency Sonar bothers blue whales as well!

The ocean noise pollution issue first came up on the general public’s sonar back in 2000 when the Navy was proposing a long distance submarine communications program called “Surveillance Towed Array Sensor System – Low Frequency Active” or “SURTASS-LFA” (in military Alphabet Soup). This system involved broadcasting low frequency signals (below 500Hz) modulated in such a way that the long wavelengths could reach beyond 1000 miles over the horizon.

The concern was that the communication channel used by baleen whales would get cluttered by the noise of this system. Some folks, alarmed at how loud it was and how far it propagated across ocean basins were concerned that the noise would deafen whales and other animals.

Ironically the lightening-rod that really brought the public out in mobs was a stranding event that happened concurrent to the SURTASS-LFA public review period. A US Navy exercise in the Bahamas using Mid-Frequency Sonar (between 1kHz and 10kHz) caused the deaths of 17 beaked whales and one minke whale – just when the Navy was telling the public that active sonar was not a problem.

The entire fracas was hugely acrimonious. The public was rightfully angry and distrustful of the Navy, and the Navy’s response fully earned the public’s distrust – by claiming that the stranding was “anecdotal” and that “the sonar didn’t kill the whales, rather they died from injuries suffered as a result of stranding.” Their strategic response was to throw gobs of funding into studies of beaked whales, conjecturing that they were the “Nervous Nellies” of the whale world.

It was believed that mid-frequency sonar only affected odontocetes – the toothed whales, because their critical hearing range overlapped the range of mid-frequency sonar. There was not much research funding aimed at mysticetes (baleen whales) at the time because there were no “anecdotal strandings” involving them.

But there were those of us in the conservation community who did remember the minke whale that also stranded in the Bahamas.

Stranded Minke Whale

Stranded Minke Whale

Somewhere between then and now it seems that the Navy decided that mitigating for bad public opinion was more expensive than doing the right thing – at least in terms of the ocean noise discussion. They started listening to the conservation and research communities, rolled up their sleeves, started funding broader inquiries and allowing the publication of work that didn’t dovetail with their preferred opinions.

One of the programs funded by the Office of Naval Research (ONR) is an ongoing study of behavioral response and “controlled exposure experiments” conducted by Dr. Brandon Southall and SEA Inc. A recent paper just published last week confirms that baleen whales do respond – and avoid mid-frequency sonar signals.

You needn’t read the whole paper to get the message, but the discussion (Section 3) is thoughtful and well written, confirming what some of us have known all along – that mid frequency sonar sounds obnoxious to everyone not just humans and beaked whales.