In summer the sound of the sea drifts up to us from the srútha, where the mountain river, looping the strand, runs finally into the waves. What keeps the Irish word alive in this anglophone corner of Mayo could be its perfect echo of the surf at this abrupt commingling of waters, commuted by distance to a never-ending sigh upon the wind. In winter, of course, when the breakers are up and the river in flood, the sigh becomes a roar and a rumble – even a rúisc, you could say (to use another of my idiomatic fragments).
How much of this, I've wondered, gets heard out there in the deep, in that "silent world", as the pioneering Jacques Cousteau, trailing noisy aqualung bubbles, was presumptuous enough to call it? Since then, of course, we have heard the lamentations of whales and the guttural gossip of dolphins, all mediated to the human ear by hydrophones. These listening microphones, invented for human wars, have brought a revelation of the ocean's living noise.
Wind-blown and breaking waves on the surface are one big source of natural noise underwater, as indeed are raindrops. But blended into this ambient sound are the noises fish make for communal reasons of their own: the broadband pulses of stridulation (grinding, strumming) or the use of sonic muscles to make knocking noises. My favourite among the latter is the humble male haddock, revving up to mating like an ancient motorbike.
The living sources of underwater sound need more research, as much of what exists – probably a great deal – has been executed and kept secret for military reasons. A lot of the increase in man-made noise comes from commercial shipping. But whales and dolphins – the cetaceans – have borne the more obvious disruption and injury, much of it fatal, from powerful naval sonars, the explosions of military exercises and the air-gun detonations of seismic surveys. Sound waves from the latter can generate 200 decibels or more.
As Ireland promotes a new licensing round of oil-gas exploration the Irish Whale and Dolphin Group has published a detailed policy on oceanic noise pollution. Its author is Dave Wall, zoologist and ship survey officer with the group, who has long experience of monitoring cetaceans in Irish offshore waters.
He spent 10 weeks last summer, for example, aboard the MV Polarcus Amani, a "multiclient" survey vessel. Keeping to straight lines between the Spanish trawlers pole-fishing for albacore tuna, it was shooting its air guns around the clock in the Porcupine Seabight and on slopes of the Porcupine Bank to produce 3D computer models of the rock strata beneath the seabed.
Wall’s job was passive acoustic monitoring through a towed device that detects sounds from whales and dolphins at times when weather and waves make sightings too difficult. However, some 3,850 animals were sighted by the four visual observers, all members of the group, and 145 sightings were recorded while the air guns were firing on full power.
Wall was also on board to monitor the Polarcus Amani's implementation of the latest "guidance to manage the risk to marine mammals from man-made sound sources in Irish waters", updated last year by the National Parks and Wildlife Service.
Assessing the damaging effects, both physical and behavioural, of the sound, it sets out detailed measures for mitigation. Seismic surveys, for example, must have experienced mammal observers aboard and should not start shooting if marine mammals are sighted within a kilometre of the air guns. In deep waters the shooting must wait for an hour after the last sighting, to give deep-diving beaked whales a chance to surface. And the firing must use a “soft start”, gradually building up the noise to full pressure.
With more and more knowledge about the foraging habits of whales migrating around Ireland, the Irish Whale and Dolphin Group now urges long closed seasons for seismic surveys – from July to the end of February, for example, within 130km of the south coast, to protect humpback and fin whales, and from August around to March on the upper slopes of the continental shelf. Other controls would apply within Dingle Bay. And long before seismic surveys of prospective oil-gas sites – at least a year and preferably two – these should be monitored for their use by cetaceans.
These are exacting demands, but they are hardly unprecedented. Canada, for example, has banned the use of seismic air guns in its whale-rich western waters. It is 24 years since Charles Haughey, as taoiseach, declared Europe's first whale and dolphin sanctuary within Irish fishery limits, to some 320km from the coastline. As times change, "sanctuary" may need to take on new meanings.