The oceans are permeated with sounds. Because the light does not reach beyond a few hundred metres underwater, sound works as sensory cues to the myriad of marine creatures, allowing them to navigate, communicate and search for food. However, the expansion of fishing, shipping, as well as of energy and infrastructure development in the past few decades has contributed to ocean soundscapes with a lot of artificial noises. These excessive sounds, otherwise called noise pollution, severely invade marine life and can pose threats to the whole ecosystem.
Because noise pollution is invisible, measuring its implications could be more difficult. However, the depletion potential of noise pollution could be really significant, from affecting diverse marine populations physiologically to changing their behavioural patterns and leading to their mortality directly or indirectly. New humpback whale deaths along the US Atlantic coast have approached 33 cases in total this year and have brought public concerns about the noise pollution in the ocean. Specifically, the concerns target offshore wind farms that are believed by some whale protection organisations to endanger whales and other marine species. In some reports we can find claims that whale strandings have happened during the wind development exploration of the sea-floor.
At the moment there is no strong scientific evidence that noise pollution can be the cause of whale mortality. However, it seems that there is also not enough research that has been done on this issue. Despite existing uncertainties, many marine researchers believe that noise pollution produced from seismic surveys, shipping and support vessels, undersea drilling, wind farms, construction etc. could have cumulative implications on marine life, sometimes really acute.
Nullker decided to collect the existing information about underwater noise pollution and dive into the question of its possible negative effects on diverse marine populations, specifically on cetaceans (whales, dolphins and porpoises). In order to navigate better in this issue we asked Whale and Dolphin Conservation (WDC) to share with us their knowledge on the topic.
For instance, marine seismic surveys, mostly used for the investigation and mapping of subsea oil and gas reserves could severely disrupt the lives of many species. The way these surveys work is the following: the air guns produce low-frequency sound pulses (airgun array = high-energy air pressure up to 300 Hz every 10-25 seconds) that penetrate the ocean bottom and reflect back to the receivers. The acoustic patterns transform into data, which enables geophysicists to construct the maps of the subsurface.
The airgun array from seismic surveys has already been correlated with mass strandings of beaked whales in the Gulf of California in 2002. In 2008 in Baffin Bay seismic surveys possibly delayed the southward migration of narwhals, more than 1000 of which died trapped in ice. Octopuses, squid, lobsters and other invertebrates also get affected by seismic surveys, becoming desensitised and more vulnerable.
More mass strandings happened around the same time in the Bahamas in 2000 and in the Canary Islands in 2002. They have been linked to high-power mid-frequency active sonar produced during naval military operations. Multiple necropsies have revealed tissue injuries near the ears, in the fluid surrounding animals’ brains as well as hemorrhages, all of which can result in the loss of navigational abilities and subsequent stranding.
WDC confirms, “Loud underwater seismic surveys (pulses of noise sent down to the seabed) to locate oil and gas, piledriving for wind turbine construction, military exercises using powerful underwater sonar, and increasing levels of boat activity all create an ocean full of noise. And levels are increasing. In 2013, a scientific analysis of the UK’s largest common dolphin stranding off the coast of Cornwall stated that the most probable cause of the event were naval exercises in the area at the time”.
Furthermore, the early stages of the construction of offshore wind farms also require hydrographic surveys. Most often multibeam sonar or seismic air gun blasts are used for this purpose. Because these surveys usually require months of continuous blasting and can be audible to marine mammals within a radius of several hundreds of kilometres, they impact a large number of species in different ways. The effects can vary from chronic stress, which can lead to the changes in behavioural patterns as well as to the damage of organs, to masking and changing the vocalisations of certain marine mammals (such as of blue whale groups). Displacements, disruptions in migratory patterns, as well as in breeding and nursing are also related to seismic activities. Moreover, tissue damage and hearing injuries (temporary or permanent deafness) possibly resulting from exposure to noise could lead to exhaustion of an animal and to alterations in behaviour. Both of which could result in vessel collision (commonly indicated as the reason for whale death) and subsequent death.
After the surveys have been conducted the pile-driving process begins, whether for resource reserves or for the construction of offshore wind turbines.
The process involves the use of massive hammers to drive steel or concrete piles deep into the seabed in order to secure the stability and longevity of the structures. While some studies found that “no form of injury or hearing impairment should have occurred at ranges greater than 100 m from the pile-driving operation”, pile-driving could possibly cause behavioural disturbances at a range up to 70 km and aversion of areas within a 16 km range. Whale and Dolphin Conservation say that “The use of pile drivers in the construction of offshore windfarms can adversely affect the behaviour of whales, dolphins and porpoises to distances of up to 40km. Noise pollution in itself, presents huge threats to whales and dolphins. [...] Noise pollution threatens whale and dolphin populations, interrupting their normal behaviour, driving them away from areas important to their survival and at worst injuring or sometimes even causing the deaths of some whales and dolphins”. In general, pile-driving operations substantially increase local sound levels. The presence of the piling vessel and support ships as well as longer periods of instalment could have more severe impacts on marine species. These operations could disrupt the food chains, cause displacement from essential biological areas, increase risks of vessel collisions and alter the habitats. Organizations Sea Life Conservation, Save the Whales, and Ocean Conservation Research mention in their statement that “behavioural aversion to noise should not necessarily be viewed as maladaptive” and that “animal removing itself from physiological harm also constitutes harm”. They point to the fact that certain avoidance behaviours such as reduced feeding and reproduction should be considered as protective practices “of the integrity of tissues and of essential biochemical processes”.
When the wind turbine is installed, machinery noise becomes the main contributor to underwater noise. As wings of the turbine operate, the produced vibrations are transmitted into the foundation and into the water. Even though the noise from operating offshore wind farms is still lower than from passing cargo ships or seismic surveys, it is static and permanent, year round for 2 –3 decades.
Image taken from Mooney, T.A., M.H. Andersson, and J. Stanley. 2020. Acoustic impacts of offshore wind energy on fishery resources: An evolving source and varied effects across a wind farm’s lifetime. Oceanography 33(4):82–95
Turbine size and their number also play a significant role in how interfering wind farms are with the lives of marine animals. Higher-capacity (15MW) wind turbines might be producing more noise pollution, especially if we consider that turbines are almost always located in a cluster of several hundred turbines. The combined and cumulative impact of a large wind farm results in the level of noise comparable to that produced by a large cargo ship (which has been agreed upon to produce the most underwater man-made noise). The overlapping of sounds from turbines could be particularly disorienting to many species as well as it could dysregulate cardiovascular health, increasing the chances of precocious death.
Without doubt, the expansion of wind energy is important for the protection of our planet. However, as the Global Offshore Wind Alliance (GOWA) has set the target to reach a minimum of 380 GW of global offshore wind capacity by the year of 2030, we need to be aware of possible negative impacts from such expansion. WDC supports the responsible development of marine renewable energy developments “in appropriate locations and in circumstances where construction and operation methods minimise impacts on whales and dolphins. Until impacts can be fully mitigated, WDC believes that new renewable energy programmes should be excluded from important marine protected areas, and buffer zones created around MPAs, so as to avoid displacing whales, dolphins and porpoises from important feeding and breeding areas”.
Underwater man-made noise is only one of the many ways we pollute our oceans that creates an additional obstacle for the peaceful living of marine species. Our ever-increasing needs for energy make us use seismic surveys, sonar and build large offshore wind farms. All of these could disrupt behaviour and lives of diverse marine creatures increasing their chances of dying in an unnatural set of events. Our goal should be to strive for the harmony of sustainable development and nature protection. And while there is still a big knowledge gap about underwater noise and its implications, exploring the ways to bring the least harm and learning about the issue is a very important step. So, thank you for reading this article!
We would be happy if you let us know in the comments how you view the expansion of offshore wind energy!