Reducing Underwater Noise Pollution: Policy Options
The murky depths of the ocean are inhabited by a wide range of animals including whales, dolphins, seals, sea lions and some fish who rely on sound to communicate, navigate, find food and mates, and engage in other activities. There is a growing body of evidence that shows the harmful effects human-made underwater noise has on these marine animals.
Observed effects include stress, hearing loss, difficulty feeding and finding mates, strandings and even death. However, these effects have mainly been measured on individual animals – proving large-scale effects on populations and ecosystems is complex and extremely challenging. The true ecological cost of underwater noise is unknown, making it difficult to weigh against the economic cost of implementing policies and strategies for reducing it.
According to this study, the main sources of underwater noise are shipping, seismic surveying for oil and gas, and offshore wind farm production. The researchers explored various mitigation options in these sectors and concluded that measures that actually reduce the amount of noise pollution are rare. Instead, interventions are often spatiotemporal, such as restrictions on activity in certain areas during fish spawning season or temporarily halting a seismic survey if a whale is detected within a certain radius. In other instances, additional noise can be used to disperse animals before emitting noise at more harmful levels. Neither of these measures address long-term effects and can only be effective if the data or observations they rely on are sufficient and up-to-date, which they rarely are.
Reducing the amount of noise-generating activity and reducing the noise emitted from this activity are the only sure ways to lower the risk of disruption to marine ecosystems. Crafting policies for environmental pollution in general falls under two categories: command-and-control (CAC) and incentive-based measures (IBM). CAC strategies set specific limits for the amount of pollution emitted, but offer no incentives to go beyond these limits. They also offer little flexibility on how and where to reduce emissions.
On the other hand, IBM’s give industries more flexibility, through a cap-and-trade system (where one polluter can trade pollution permits with another) and through economic incentives to reduce pollution by emissions subsidies or taxes. But whereas a cap-and-trade system is suitable for a universally mixing pollutant like CO2, noise pollutants trade with permits of unequal value due to differences in location and timing.
Commercial shipping is the most widespread source of underwater noise. Shipping vessels generate a low-frequency noise which is similar to that of many marine mammals. With global trade ever-increasing, levels of shipping noise pollution are also projected to increase. Measures to reduce the noise from shipping vessels include modifying propellers and/or hulls and performing regular maintenance, vibrationally isolating machinery, implementing ship speed restrictions and incentivizing the use of fewer, larger vessels.
Driven by renewable energy targets designed to reduce CO2 emissions, the amount of power generated by offshore wind farms is projected to grow sixfold in the next decade. The noise generated by operating wind farms is low, but construction includes driving steel cylinders into the seabed with percussive piling hammers. This is a comparatively temporary source of underwater noise, but it generates high amplitude pulses which have been shown to distress and displace nearby marine animals. Mitigation options include finding alternative foundations such as floating bases, placing acoustic barriers such as bubble curtains around the piling operation and incentivizing the installation of fewer, larger turbines.
Seismic surveys are mainly conducted in search of oil and gas reserves. The surveys use airguns that release pulses of low-frequency sound, and their effects can include auditory damage, displacement, and increased mortality of various marine mammals, fish and zooplankton. There is a promising alternative to airguns known as marine vibroseis, which produce less noise while producing equal or better seismic data. However, there is currently no incentive to use quieter technologies and no regulatory pressure to reduce noise at all. An incentive-based approach would follow the polluter pays principle (PPP) and revenue from levies could be used to develop alternative technologies and to study the effects on surveys on marine life.
While climate change and an ever-growing human presence in our oceans are already taking their tolls on marine ecosystems, reducing underwater noise pollution is a relatively manageable way to reduce our impact. The three industries highlighted in the study all have policy options available for noise reduction, and carefully crafted policies should be able to effectively reduce noise pollution while avoiding unnecessary disruption to important sectors. Armed with this knowledge, marine life advocates can help to push for such policy options, and help to bring the public on their side.