Dolphins raise sound questions
For Captain Nemo, the coral ocean depths made a "quiet grave", one that all submariners should desire; but if Jules Verne's inventive genius were to pilot his Nautilus through the world's oceans today, he might find it a much noisier place.
Report after report in recent years has identified rising noise levels in the seas as a potential threat to marine life, particularly mammals that rely on sound for communication and hunting - which principally means whales, dolphins and porpoises.
The sources of sound range from the diffuse chunterings of ships' propellers to the sharp sonic shocks of seismic explorers - and military sonar, which has been directly implicated in mass strandings of beaked whales, an enigmatic group of species that seem especially vulnerable to the intense blasts of submarine-hunting soundwaves.
It adds up to a complex picture, and one for which there are few definitive answers, notwithstanding a long-running sequence of legal cases between the US Navy and conservation groups that has seen the latest science unveiled in court.
So it was with some interest this week that I opened the electronic pages of the Royal Society's journal Biology Letters to read what claims to be the first empirical proof of the physiological impacts of naval sonar on dolphins.
It comes from the University of Hawaii. Working with a single captive trained bottlenose dolphin, Aran Mooney (who's subsequently moved to Woods Hole Oceanographic Institution) and his team "presented" - as they say in acoustics jargon - blocks of sonar pings, and measured their effect on the animal's hearing threshold - the quietest sounds it could detect.
When the sound level of the sonar was racked up enough (to a sound energy level of 214dB, for the technically minded), it produced a temporary hearing loss - akin, Dr Mooney told me, to the sort of thing you or I might have after standing next to the bass bins at a Metallica gig. It disappeared after 20 minutes or so.
Translating these sound levels into the real world and looking at the equipment that anti-submarine ships actually use, the team calculated that a dolphin would have to spend about two minutes within 40 metres of the sonar source in order to suffer this hearing loss.
Aran Mooney's view is that this means military sonar is going to crop up rarely as a significant problem, and that should be manageable - simply avoiding its use when cetaceans are close should, in the vast majority of cases, avoid harming them.
So far, so good. But lying behind this research is, I would suggest, a much wider and more important issue; how little we really know about the impacts of marine sounds, and how difficult it is going to be to get the answers we really need.
For a starter, the species of most interest, the beaked whales, live very different lives from the ebullient and assertive bottlenose dolphin.
Secondly, the prevailing theory holds that naval sonar wreaks its damage not through harming the animals' hearing, but because they change their dive pattern in response to the sound.
That might be because it resembles the calls of killer whales; whatever the reason, the result is that the whales contract a fatal condition similar to "the bends" that affect human divers.
And if myriad other quieter sounds are harming cetaceans, they must be acting by disturbing or disrupting the animals' behaviour - they are simply not loud enough to cause even temporary deafness.
I called up Mark Simmonds, director of science at the Whale and Dolphin Conservation Society, to see what he made of it; and the answer was, not much.
"Finding that if you expose animals to loud noises you're likely to deafen them is hardly telling us something we didn't already know," he said.
But the wider point, he said, was that focusing on the narrow direct effects of sonar might deflect attention from the behavioural issues, which are the really important ones.
So let's think big thoughts for a moment and ask what kind of research you would really like to do on this question if your resources and ingenuity were boundless.
Firstly, I think, you would understand more of the raw, natural behaviour of the species of interest in the wild.
But so little is known about beaked whales - even how many there are and where they live - that this is actually a huge, vast undertaking, despite the recent successes of researchers working in the Canary Islands who have managed to tag a couple of species with instruments that can follow their dives and monitor the sounds around them.
Assuming that you could do this, you would then observe how the animals respond to a range of sounds - including the calls of killer whales and military sonar - in the wild.
A poor substitute in theory might be to take a beaked whale into captivity and do the kind of "laboratory" experiment that Aran Mooney did with his dolphin - but for a huge variety of reasons, including the ethics of doing this with rare species and the practical issue that beaked whales feed on squid up to 2km underwater, it's unlikely ever to happen.
Another issue is that the beaked whale deaths directly linked to military exercises make up a tiny proportion of all cetacean strandings.
Within the last few months, pilot whales, sperm whales and bottlenose dolphins have all stranded on southern Australian beaches; whether the root cause is related to sound is still a mystery, and so is how we might research it.
Expanding to the full field of sound impacts, you might like to investigate fully the baseline behaviour of all cetaceans and then how it changes in response to seismic exploration on the sea bed.
Then - we're getting to the really tricky stuff now - you would compare how some of the baleen whales such as the giant blue behave in noisy and noiseless oceans, to see precisely how their long-range communication is hampered by the cavitation of thousand of propellers above their heads.
To be frank, most of it these ideas are at present a pipedream, and likely to remain so.
The core recommendation of conservation groups, then, is to reduce all ocean noise. Propellers can be designed to be quieter, use of military sonar and mineral exploration airguns can be kept to a bare minimum and eliminated entirely in areas of ecological importance.
But there is still a thirst for more direct research.
The danger is that when logistics curtail the science we would really like to do, we end up doing what we can, whatever its degree of relevance, and perhaps extrapolating further than we should from the findings.
According to one recent study, the level of noise in Pacific waters is doubling every decade. Another tells us that acidification of the oceans will mean sounds travelling further - potentially, again, disrupting the long distance communications of whales.
There is clearly an ocean of relevant research waiting to be done. Whether any of it involves playing loud sounds to dolphins inside pens, I am less sure.