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Tiny bubbles and military sonars give cetaceans "the bends"

Cetacean Society International

Whales Alive! - Vol. XII No. 2 - April 2003


The September 2002 stranding of Cuvier's beaked whales in the Canary Islands was caused by what human divers call decompression sickness (DCS), or "the bends".

Until now the standard belief was that cetaceans couldn't suffer DCS, because they dove deeply with only a small remnant of air in their lungs from their last breath. DCS afflicts humans that breathe extra air from tanks while submerged, and then come to the surface without taking enough time to get rid of the nitrogen saturated in their body's tissues. DCS is the result of nitrogen coming out of solution and forming bubbles that expand to disrupt cells, cause loss of function in organs, create embolisms that block circulation, and compress or stretch blood vessels and nerves. DCS in humans has several levels of severity, and by itself is not usually fatal, but it is often crippling.

These stranded whales had evidence of fat embolisms, and "severely disseminated microvascular hemorrhages", which means that they had blood around nerves, eyes and brains, and in their ears, lungs, kidney and spleen. Not every whale had all the symptoms. They might have survived, but thoroughly disoriented and suffering from multiple injuries, they blundered ashore, at least giving the superb scientists in the Canary Islands the clues to tell us all what happened.






Cuvier's beaked whale.

Photo courtesy Pascual Calabuig,

Center of Wild Life Care of Gran Cannaria.







There have been over 20 mass strandings of beaked whales since detailed records began about 1963, when modern sonars appeared. But the connection between strandings and sonars wasn't made clear until an event in Greece in 1996. The great majority have been Cuvier's beaked whales, but dense beaked whales and other species have been mixed in. After the 2000 stranding in the Bahamas the focus of investigations was on the whales' heads and ears, with implications for hearing and orientation.

Only after the Canaries stranding did the investigations widen to look for evidence of DCS in major organs. Recently, DCS symptoms have been found in stranded Risso's dolphins, common dolphins, and even a harbour porpoise, all in the UK. One dolphin's liver looked more like bubble wrap than tissue, but the dolphin had lived for some time before stranding, perhaps from other causes.

How many previous strandings have offered clues that have been missed? For example, blood flowed from the eyes of some stranded beaked whales in the Canaries, Greece, and the Bahamas. Many things could cause this, but even media reports might make a note of it. Every such historical record should be reviewed for any correlation with military sonars before the stranding. Another concern is that even a single beaked whale that strands might mean sonar impacts on an unknown number of whales over a wide area, only one of which made it to shore. A beaked whale mass stranding can often be of very separated individuals, implying a scattered feeding group where only the closest whales blundered on shore. And could DCS have caused the stranding of the two minke whales involved in the 2000 Bahamas event?

Military sonar is the culprit because there is no evidence so far that Cuvier's beaked whales or any other deep diving cetaceans suffers from DCS naturally, after millions of years of evolving to exploit the deep ocean.

Look what happened on that fateful September day in 2002:

Sometime before dawn off the Canary Islands of Fuerteventura and Lanzaote a veritable storm of military sonars were unleashed as the "Neo Tapon 2002" naval exercises began. At least 58 surface vessels, six submarines, and 30 aircraft participated in a mock assault that included assets from several nations, first identified as a NATO manoeuvre. The strandings started sometime soon after.

The behaviour of Cuvier's beaked whales may make them vulnerable to sonar noise. If the whales spent very little time at the surface between dives, dove up and down slowly, stayed very deep as long as possible, and had some air in their lungs during the first 70 meters of the dive, the whales' body tissues would likely become supersaturated with nitrogen. That nitrogen would be even more dangerous if the whales rushed to the surface, perhaps if they were startled. Cuvier's beaked whales have been doing such dives for millions of years, so what was different here?

Suddenly there were multiple military sonars pinging, each sending half-second pulses at about 2-3.3 kHz every 24 seconds or so, with source levels perhaps as high as 235 dB re 1 ÁPa. There were deep canyon walls and maybe water "ducts" to reflect and channel the sound energy. Perhaps it was a sudden rhythm or beat, or several waves striking from different directions at once, but something about the way each whale was struck made a terrible difference. The extensive analysis of the sonars and environment that were implicated in the 2000 Bahamas stranding could only conclude that the combined sonars of several ships had been "ducted" by specific water conditions.

What follows is theory only, questions to be answered.

The disaster may start with the "microbubbles" in the tissues of many deep diving cetaceans. Why don't these nearly microscopic bubbles expand every time a whale surfaces from a deep dive? Or why don't they dissolve? To summarize all the big technical words, that's still a mystery. Perhaps, according to a theory from acoustical physicist Professor John Potter, a protein based nonpermeable barrier forms naturally around the microbubbles. No one has noticed it, but has anyone looked for it?


Whateve usually keeps these microbubbles stable may have protected cetaceans from naturally occurring DCS for the millions of years they've exploited very deep habitats.

So, if the sounds from multiple midrange military sonars were manipulated by certain water conditions and struck an ascending whale with extremely saturated tissues, the microbubbles might pulse enough so that their gas-impermeable wall cracked. As the wall broke up after the initial expansion, the bubbles' size would multiply rapidly by static diffusion and cause significant damage in a very short time. Another process, called rectified diffusion, could also explain the bubbles' expansion, but received levels of sound over 210 dB would be required even for supersaturated tissues.

It's very important to recognize that the received level of sound that initiated the bubbles' expansion might have been only 140 dB or even less, far below the often-used 180 dB level officially considered to be the threshold of injury. Until the full picture of this complicated event can be documented no one can say what really is a safe level of sound. But there should be no question that relatively low levels of sonar sounds under certain conditions cause DCS in cetaceans.

Do No Harm
There are a lot of questions that have to be answered before the threat of sonars can be reduced. Even if operational changes are made to lessen the chance of impacting whales, such as avoiding likely beaked whale habitats or with pauses giving them a chance to escape, the world's navies will demand proof. Even then, the political will needed to force the navies to stop crippling whales with sonar may need very dramatic proof.

There are many other questions that reasonable people must ask about the harm human noise does in the oceans. Without answers managing and mitigating that noise is only guesswork, without the facts to support whatever solutions are proposed or required. Adequate and appropriate science must provide those facts. But at this moment research that would use sound on live, wild cetaceans has almost stopped, particularly in the US. In January a lawsuit succeeded in stopping a project designed to see if whales could be located with sonar. Earlier a seismic survey implicated in the deaths of two beaked whales refused to stop until a judge ruled that it must. Funding agencies watched as the research teams idled and the resources, money and time vanished. Suddenly legal challenges have become a major obstacle to all future research.

The sonar lawsuit found that NOAA Fisheries had failed to meet the obligations of the National Environmental Policy Act (NEPA), by amending a 2000 permit three times, adding oceans, species, noises, and purposes, all without a public assessment of impacts. The judge stopped short of opening MMPA and other issues, but they were there.

The fundamental motivation to legally challenge noise research today is the perception that the research will do harm. The plaintiffs in the sonar lawsuit were motivated first to stop the project for the ethical and moral reasons; they believed it would harm migrating gray whales, some pregnant, some newborn calves. Empowered by these recent court decisions, frustrated by government slackness and scientific silence, more whale advocates today stand ready to oppose any acoustical research on live cetaceans. It's a matter of trust.

Advocates may agree that science is about finding facts, that those facts can prove the harm done by human noise, and that advocates can use that proof to win back protections. But, after too many frustrating examples they simply don't trust scientists or agencies in general, because of several perceptions:

First, that the conclusions from a project may be biased in favour of the funder. It is a fact that very few US scientists that receive funding from the US Navy's Office of Naval Research have made any public comments of concern about military sonars, like the LFA, while many, many scientists elsewhere, not caring about ONR funding, have been very vocal. ONR rejects the notion of such influence, but many scientists admit to it. Other major funding sources are perceived to have similar influence, true or not. One solution CSI and others are working for is the creation of an impartial intermediary that would receive the funds and distribute them without influence. Funders such as ONR are already objecting.

Second, that scientists are willing to harm cetaceans in order to get results. Some are, but most are not. But advocates believe that scientists have lost sight of why they started in the first place, and now look at the world as if it was all organic machines and chemicals, a source of funding, publications and tenure. Scientists see advocates as too subjective and emotional, selecting what to believe even if it has no basis in fact. They often don't know how to talk to each other, even if they wanted to.

Third, scientists can be very reluctant to express an opinion without empirical proof. They qualify every comment, just to make sure. Yet, as experts, they are expected by advocates to have opinions, and to be willing to show that they care enough because they know enough. Scientists should feel free to express their opinions, but many feel constrained by peer pressure to stay detached.

Fourth
, scientists and regulators don't communicate clearly with the public. Terms like "biologically significant impacts", "population level events", "biological relevance", or "controlled exposure experiments" may be useful in professional contexts, but they don't work when advocates just want to know when whales and dolphins are being harmed and what responsible people are doing about it. For example, while "controlled exposure experiments" are used to explore the potential for noise to have harmful effects on marine mammals by making noises, they do not often publicly assess and minimize the risk that the experiments themselves may harm their subjects. That's enough to turn most advocates towards legal solutions.

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