What’s the danger for the whales?
Despite what Jacques Cousteau used to say, the oceans are far from being the “world of silence”. The wind, shifting tectonic plates and the calls of the whales compose a complex soundtrack. But over the past 50 years, human activities have completely transformed this soundtrack. Some go so far as to call it noise pollution, and biologists are concerned about its effects on marine mammals. Why? On one hand, the oceans have become awfully loud, and noise levels continue to escalate. On the other hand, marine mammals depend on sound for navigation, feeding, reproduction and socialization. Along with hunting, habitat loss and chemical contamination, noise is now recognized as one of the biggest threats to marine mammal survival.
Shipping, the mining and oil industries, military activities, acoustic thermometry, and fisheries all contribute to the relentless increase of sound levels in the oceans. Furthermore, all these sounds might travel up to 70% farther by 2050 with the rising ocean acidity caused by greenhouse gases.
With globalization, the merchant fleet has surged and is anticipated to double again by 2025. All these ships (oil tankers, tugboats, freighters, icebreakers, etc.) fill the farthest reaches of the oceans with a constant roar in a frequency band in the 500 Hz range. Drilling activities are also a significant source of low-frequency noise. For example, oil exploration requires the use of a compressed air gun array towed behind a boat, which produces tens of thousands of explosions. In fact, from exploration to production all the way through to the dismantling of facilities at the end of a site’s service life, every stage of hydrocarbon extraction beneath the ocean floor adds to noise levels.
The US military and NATO also contribute to rising sound volumes in the oceans. In order to detect today’s ultra quiet submarines, they have developed low-frequency active sonar systems (LFA). These systems don’t just listen, they also produce powerful sound beams (230 dB at the source) that fan out in all directions for hundreds of kilometres.
Low-frequency sounds travel great distances, and this characteristic makes them an interesting research tool. Since the speed of sound is a function of temperature, the mean water temperature can be calculated by measuring the time it takes a sound to travel a known distance. As part of the ATOC program (Acoustic Thermometry of Ocean Climate), American researchers placed in the Pacific two transmitters (one in California and the other in the Hawaiian Archipelago) and about a dozen receptors in order to study climate change. For ten years, these transmitters produced sounds of 195 dB at regular intervals. The same group of scientists is contemplating placing such transmitters in all the world’s oceans.
Fisheries have also contributed to noise pollution in their attempts to address the problem of marine mammal bycatch in fishing gear. Fishermen install sorts of “acoustic scarecrows” in order keep whales and pinnipeds at bay. The effect of these sounds is relatively localized compared to that of the noise sources discussed above. Nevertheless, these sound beacons aim to produce an effect on marine mammals and might have significant impacts on the use of critical habitats by coastal species such as the harbour porpoise. Lastly, the construction of offshore infrastructure such as ports, oil and gas platforms, tidal and wind power projects, etc. also help ratchet up the decibel level in the oceans.
…a hazard for whales?
The effects of noise pollution depend on the distance from the noise source, among other factors. If the sound is powerful and the animals are in close proximity, it could lead to permanent damage to the ears, internal injuries or even death. Less acute sounds can also result in temporary deafness, as demonstrated by studies conducted on seals, dolphins and belugas in captivity. Previous studies on whale strandings during military exercises have even demonstrated that the animals showed internal injuries, notably in the internal ears and cervical areas. The United Nations, the US-based National Oceanic Atmospheric Administration (NOAA), and the International Whaling Commission (IWC) have suggested that there could be a link between the use of military active sonar and cetacean strandings.
A study published in February 2012 and conducted on the feces of North Atlantic right whales in the Bay of Fundy demonstrated that the greater noise pollution is, the higher the so-called stress hormone will be. It was in the context of the events of September 11, 2001 that researchers were able to establish this correlation. Indeed, on this day, traffic diminished considerably and the volume of acoustic emissions emitted under the water surface fell by half. No seasonal or occasional drop in hormone levels such as the one measured in 2001 had ever been observed in whales in previous studies.
Further, if exposed to multiple sources of stress, whales might also suffer from diving-related decompression accidents. Indeed, this type of intense sound may have a direct impact on nitrogen bubble formation or on the behaviour of whales, which might alter their dive profiles (time and depth), exposing themselves to excessive tissue saturation and significant gas bubble formation. These results – obtained from a seminar bringing together some twenty international experts in diving-related physiology in both humans and marine mammals – are published on the Internet site Proceedings of the Royal Society B.
In addition to the physiological effects, anthropogenic sounds can impact cetaceans’ behaviour. Studies have shown that relatively acute sounds can cause whales to deviate from their trajectory or reduce their time spent feeding. Chronic exposure might even force marine mammal populations to abandon habitats. Some species of cetaceans stop vocalizing for several hours or even several days when they are exposed to low-frequency sounds. Moreover, even thousands of kilometres away from any noise source, whales might suffer from increased background noise in the oceans, which is likely to mask certain important sounds. This effect may make the difference between detecting a prey or not, escaping a predator or not, locating other pod members or not. This form of pollution is all the more alarming in that the frequency bands used by whales coincide precisely with those that have increased the most in the oceans. In certain maritime zones, the distance at which blue whales communicate is even believed to have shrunk by 90% due to increased noise.
Unfortunately, there is a paucity of data available to evaluate the real problems presented by noise pollution. Published studies are particularly oriented toward short-term effects, and raise many questions. What do these reactions really mean for animal biology? When no reactions are apparent, are the animals truly out of danger? What about the rest of the ecosystem? Might whales be suffering from noise pollution through the latter’s impact on their food sources? Biologists don’t yet have the answers to these complex questions. In the fall of 2011, the International Quiet Ocean Experiment was launched. Undertaken over a 10-year period, this program aims to acquire scientific knowledge on marine noise pollution and its impacts on organisms, and to coordinate research on an international scale. The objective is to fill knowledge gaps in this still poorly understood field and to envision measures to mitigate the impact of harmful noise pollution.
Regulating noise pollution… a formidable challenge
Although the issue has been known since the 1970s, initiatives to mitigate it are relatively recent. Reports published in 2008 by the European Science Foundation and the National Marine Fisheries Service (NMFS) all advocated the establishment of standards to address noise pollution. After years of legal battles, a coalition of environmental groups headed by the Natural Resources Defense Council (NRDC) announced in 2008 that it had reached an agreement with the American Navy. The Navy, recognizing the impact of its sonars on cetaceans, undertakes to finance research, prepare impact assessments and make information on its sonars publicly available.
Certainly, long-term monitoring of the impact of noise pollution on ocean life in general and marine mammals in particular is essential. International cooperation shall also be promoted in order to identify solutions to recognized problems and practical means of implementing noise reduction standards. These are major challenges when one considers the wide array of activities that contribute to ocean noise pollution. In fact, this form of pollution is but one aspect of a broader problem (and one of the concerns of the United Nations environmental program): our growing use of the oceans.
And in the St. Lawrence?
Maritime traffic combined with the local topography creates some of the noisiest environments in North America, such as the mouth of the Saguenay Fjord. Construction of offshore infrastructures or gas exploration raises serious concern for the integrity of the St. Lawrence, notably with regard to noise pollution. Chronic stress has physiological effects, particularly on the immune system. Daniel Martineau, veterinarian at the Université de Montréal’s faculty of veterinary medicine, has been monitoring pathologies in St. Lawrence belugas since 1982. He points out that stress can act in synergy with contaminants and lead to even more acute effects to weaken the immune system, especially in young animals. What if this constant noise that we impose on belugas compromised their chances of facing all the threats to this fragile population?