Further to yesterday's press conference here in Rome about the threat posed by marine noise pollution, here is a summary of the evidence:Navigating the oceans of noise
Underwater noise pollution is a significant threat to whales, dolphins and porpoises, but one that is still in many respects poorly understood. These are animals that primarily experience their world acoustically and, as such, they can be expected to be especially vulnerable to changes in the marine acoustic environment. The available evidence more than supports this. Increased noise levels may produce an acoustic fog which prevents them communicating normally. Previously, some of the larger whales may have been in communication across entire ocean basins and now such long distance communication may be drowned out by human noise. The full implications of this for these animals are unclear but an important function that may have helped distant animals find each other and perhaps also their key habitats may now be compromised.
Noise may also startle and disrupt normal activities as it does for terrestrial animals. When these activities include breeding and feeding or migration, population level impacts may be induced. Historically, in some countries, loud noise has even been used to drive whales in hunts, and there is growing evidence that loud noise today has inadvertently caused strandings and death. In particular, unusual multiple mortalities of deep diving beaked whales have been associated with certain military sonars. Whales from these events have been found to have distinctive embolisms in their tissues (similar to the lesions caused in human divers in the condition known as the ‘bends’) and the most likely mechanism for their production is that the whales exceed their physiological tolerances by being forced to change their normal diving patterns, perhaps as a panic response to loud noise. It is also possible that loud noise may directly cause damage to organs at high exposure levels. The same embolisms have recently been found in other species indicating that they may too be affected. In fact some non-beaked whale species have been associated with unusual stranding events, including high profile events this year in the UK and Madagascar which are still being investigated.
Furthermore, a rather unexpected link has recently been made between rising levels of CO2 in the atmosphere and ocean acoustics. As sea water becomes more acidic, in addition to other effects, scientists have recently calculated that this will change underwater acoustics and make the seas noisier, with potential knock-on affects for cetaceans and human activities. The researchers concerned commented that ‘Ambient noise levels in the ocean within the auditory range critical for environmental, military, and economic interests are set to increase significantly due to the combined effects of decreased absorption and increasing sources from mankind's activities’.
The main sources of loud extraneous noise in the oceans are boat traffic (typically the bigger vessels are the noisier ones at least at lower frequencies), seismic surveys (as used in marine fossil fuel exploration and monitoring) and military exercises. Perhaps not surprisingly, the links between military activities and problems for whales have proven to be highly controversial and hotly debated. They have also been the source of numerous court cases in the US and the matter has even reached the US Supreme Court and the White House.
Noise pollution should be regarded as an emergent threat and parallels can be made between our current state of knowledge and where we were with chemical pollution and the threat that it posed to cetaceans some decades ago. Cetaceans, as deep diving marine animals, are particularly difficult to study and there are good ethical reasons (as well as practical ones for the larger species) that quite rightly inhibit exposing them to potentially harmful stimuli. In the 1960s and 1970s it started to become clear that cetaceans were likely to be vulnerable to the immunosuppressive and reproductive-impairment effects of certain ubiquitous chemicals. The evidence was based on high levels identified in their bodies, rapid transfer of these substances to their young and knowledge of how such substances affect other species. In other words, the evidence was circumstantial but pointed towards a significant problem. However, showing a simple cause-effect relationship was illusive. Fortunately action to address this nascent threat did not wait for such proof. Most recently studies based on large numbers of stranded bodies have strengthened the evidence that cetaceans are harmed by some chemicals because, for example, measurable effects on immune function can be seen above certain levels in tissues.
In the case of noise pollution, the evidence is again based on exposure levels, some field observations and some pathology (some of it very unusual), but like other threats in the environment, ‘scientific proof’ is again notably hard to find, and, arguably, this is not helped by some aspects of the issue being of so high profile. Hence we are in a situation where we are weighing the evidence; a situation where the evidence indicates a significant problem requiring a precautionary response. The International Whaling Commission recently looked at this matter and identified (IWC Resolution 1998-6) the impacts of anthropogenic noise as a priority topic for investigation within its Scientific Committee, and that the Scientific Committee, in its report to the 56th meeting of the IWC, concluded that military sonar, seismic exploration, and other noise sources such as shipping pose a significant and increasing threat to cetaceans, both acute and chronic, and made a series of recommendations to member governments regarding the regulation of anthropogenic noise.
The question for CMS at this COP is how to best address the threats posed by noise pollution. CMS has already accepted this as an issue (CMS Resolution 8.22) and now needs to find an appropriate way forward. We recommend the development of precautionary guidelines and clear advice to parties, building on and linked to ongoing work conducted under the auspices of ACCOBAMS and ASCOBANS, and designed to reduce noise levels and mitigate the effects of noise pollution of all kinds. We also recommend an ongoing vigorous dialogue with other relevant bodies.
For more information see:
WDCS publication ‘Oceans of Noise’ available as a PDF at: http://www.wdcs.org/submissions_bin/OceansofNoise.pdff
L.S. Weilgart 2007. The impacts of anthropogenic ocean noise on cetaceans and implications for management. Canadian Journal of Zoology 85: 1091-1116.