We don’t know enough about the effect of noise on marine life to take any chances.
A recent study found that human-caused noise pollution in the oceans might inflict severe trauma on marine life, causing damage to hearing and orientation structures in squid and octopuses. The study has renewed interest in the growing problem of noise pollution, as the Nova Scotia government currently studies the possibility of opening up Georges Bank to oil and gas exploration. It’s a move critics say could lead to noise pollution damaging one of Canada’s most lucrative fishing areas.
By now we should know that the oceans are facing myriad threats. We know about chemical pollution, marine debris, over-fishing, by-catch, etc., but how many of us know of another insidious threat to marine life, namely ocean noise? We are mainly visual creatures, so we cannot relate well to most marine species that rely principally on hearing. Water conducts sound so efficiently that noise can travel hundreds, even thousands, of kilometres before fading into the background.
Raising the level of human-caused noise is akin to blanketing the oceans in an ever-denser smog. Maybe the smog lifts momentarily, maybe there are pockets of clarity, but in general, animals will have more trouble finding widely dispersed mates, prey, and group members. They will encounter difficulty in finding their way, and in avoiding dangers like fishing nets and predators. This may result in more by-catch (e.g., dolphins getting caught in nets), more collisions between ships and whales, and animals having a harder time finding the dwindling numbers of prey that are still left.
Human-caused undersea noise is mainly the result of shipping, seismic air-gun surveys used by the petroleum industry to locate deposits under the sea floor, and naval sonar. And the problem is only getting worse. Noise levels are increasing steadily, doubling every decade for the last half-century. Recently, a 10-year study using listening devices on the mid-Atlantic sea floor found that seismic air-gun noise was nearly omnipresent. Seismic surveys for oil and gas could be heard thousands of kilometres away, from Nova Scotia, Brazil, and Africa – such is the far-ranging reach of ocean noise. Can such a dramatic change to an ocean’s environment go unnoticed by marine creatures? It’s doubtful. Marine mammals, fish, and even invertebrates seem to be sensitive to sound.
Why, then, would Nova Scotia even consider lifting the moratorium on seismic surveys on the highly productive Georges Bank? These are some of the best fishing grounds in the world and home to the highly endangered North Atlantic right whale. The bank straddles the U.S.-Canadian border, located between Cape Cod and Nova Scotia. Yet the Department of Fisheries and Oceans is currently conducting a review to inform decision-makers whether Georges Bank should be opened to oil and gas exploration. The moratorium on exploration has been extended to the end of 2015, which is a good decision in light of the dangers of noise to marine life.
While it is hard to avoid the pervasive, trans-boundary nature of marine noise entirely, we can at least safeguard biologically important habitat. Some such habitat should be set aside in Marine Protected Areas (MPAs), with adequate buffer zones to protect marine life from noise.
MPAs can be especially effective in the management of complex interactions between threats. Marine animals rarely face just one threat; they usually encounter several simultaneously. These stressors can interact in often unpredictable ways. For instance, climate change has produced ocean acidification, both of which are serious threats on their own. However, ocean acidification also improves the transmission of sound, particularly lower-frequency sound that dominates noise, meaning that noise will travel even greater distances.
Who would have predicted that burning fossil fuels would indirectly cause noise to extend its reach across oceans?
By protecting productive and sensitive habitat from as many threats as possible using MPAs, we don’t need to know the details of how such threats may interact – we simply try and keep all harm at bay.
The ocean is opaque, and whales spend little of their lives at the surface. Whales are hard to predict, especially their behaviour, which can vary depending on the time of day, past experience, context, age, sex, species, etc. Trying to tease apart all of these factors is a challenge.
After years of studying whales at sea, I have concluded that, if we want to protect marine life and its habitat, we are safest in reducing threats to their minimum. This does not mean balancing the needs of noise producers, and that of marine life, on a knife’s edge. Our knowledge is too incomplete to master such perfection. Rather, let us admit to uncertainty and keep noise away from sensitive marine life such as on Georges Bank, reduce noise levels to their minimum, and set aside MPAs.
Tinkering carelessly with the oceans has usually gotten us into trouble. Clearing the acoustic smog, on the other hand, will almost certainly help.
Photo courtesy of Reuters.