By Charley Elias
Beneath the ocean’s surface, the underwater world is dominated by sound.
It is a cacophony of both natural and human-made (also termed anthropogenic) sounds that echoes through the sunlit surface layers to the twilight zone and further still into the oceanic depths. Physical/geological components such as the roaring and crashing of surface waves, the racing surge of underwater currents, and the shifting and rumbling of rock or sandy substratum are some sources of natural underwater sound.
Additionally, biological noises that are produced by the vast diversity and abundance of marine life that dwells in all oceanic habitat zones also contribute to this submerged symphony. Biological sounds include a diverse range of noises that can be heard as snaps, pops, buzzes, clicks, croaks, whistles, squeaks, barks, grunts, and many more from a variety of invertebrate and vertebrate life forms.
For fishes, sound-production is made by the grinding of their teeth, throat muscle vocalizations, or the tightening and loosening of their abdominal muscles to vibrate their swim bladders. For invertebrates, sounds can be produced by oversized-claws or other body appendages. However, not surprisingly, the loudest and farthest-ranging sounds in the marine animal kingdom are the ones made by the great whales.
It has been reported that the deep and loud vocalizations made by blue and fin whales are capable of travelling across entire ocean basins.
Another category of underwater sounds consists of anthropogenic noises that include: propeller blade cavitation from commercial ocean-going vessels; motors of recreational watercraft; seismic blasting for underwater exploratory surveys; naval sonar testing; and industrial pile-driving machinery used for offshore drilling and construction.
Altogether, both the natural and human-made noises produced on and/or beneath the ocean’s surface create a rich, loud, and dynamic oceanic soundscape. However, within the timespan of the past 60 years, increased worldwide technological development and exponential growth of human populations and commerce across the globe have caused our world oceans become dramatically louder and noisier in terms of abundance, intensity, duration.
The result is in an overwhelming amount of underwater noise pollution. Over the last two decades, more attention has been paid to this serious environmental issue, and focused studies have been conducted on the impacts of human-made sounds on various groups of marine animals and ecosystems. Scientists have reported significant increases in the ambient (aka background) noise of the oceans and have found that some anthropogenic sound sources detrimentally, and at times fatally, impact marine animals in several major ways:
- Cause marine animals to dramatically change their natural behavior as it pertains to feeding, mating, migrating, locomoting, evading and hiding from life-threatening danger.
- Prevent marine animals from hearing sounds critical to their immediate survival. This is termed masking. Masking reduces communication distance between members of the same species, and can cause accidently misleading information to be relayed among the individuals attempting to communicate with each other.
- Cause temporary and/or permanent hearing loss, severe damage to auditory and equilibrium sensing tissues and organs, and ultimately result in death. Damage to hearing structures can worsen over time even though the noise has lessened or stopped.
- Strandings of marine mammals, particularly of toothed whales (sperm, pilot, and beaked whales) as well as those of small cetaceans (dolphins and porpoises).
In well-documented studies of impacts of underwater noise pollution on marine mammals, extremely loud and persistent underwater anthropogenic sounds have numerous harmful, even fatal, impacts on their physical health, feeding, mating, and social behavior. Noise from large ships and commercial vessels overlap the low-frequency sounds that many whale species use to communicate with each other, locate food, and mate.
In the waters of Cape Cod Bay, the sounds of commercial shipping traffic along this coastal waterway have caused an 80 percent decrease in the acoustic space of the critically endangered North Atlantic right whale of which there are only 411 individuals remaining. Acoustic space refers to the distance of the individual whale’s vocalizations and those of other conspecifics. This noise has severely compromised their forging and feeding behavior. Additionally, the underwater noise pollution from oceanic shipping traffic is known to interfere with and compromise the communicative abilities of blue and fin whales.
Seismic exploration of the benthic seascape for natural resources (aka oil and gas), is driven by a global fleet of approximately 100 specialized oceanographic vessels, 20 percent of which are conducting field operations at any one time during the year. Behind these specialized vessels are towed mechanical arrays of various-sized air gun apparatuses. The air is released under extremely high pressure and creates a powerful underwater sound wave that penetrates miles beneath the seafloor and then radiates upward and outward. The subsequent examination of the resulting sound waves allows engineers and geologists to map out sections of the ocean floor and determine where are the likeliest locations for the most productive oil and gas deposits for subsequent extraction.
During a seismic survey, the air-gun arrays are fired at regular intervals – approximately every 10 to 15 seconds for a maximum duration of 24 hours per day that can last weeks or months at a time! Underwater, the seismic blasts emitted from the towed seismic arrays have astonishing sound-producing capabilities of up to several hundred nautical miles away from the source. According to several studies, the noise from these seismic blasts is so loud, even at large distances away from the source vessel, that it has “drowned out” whales’ vocalizations as well as other naturally occurring ambient sounds. Unsurprisingly, the resulting scientific observations and reports from these field studies have shown that these seismic air-gun surveys produce severe ecological impacts on marine life, both big and small. Great whales and smaller cetaceans were adversely impacted by the seismic air-gun blasts with significant behavioral changes. These included the immediate and prolonged silencing of vocal communication, as well a leaving productive feeding areas through the duration of seismic surveys, only to return to their feeding areas and resume vocalizations days after the seismic surveys activity had ceased.
Marine mammals are not the only creatures of concern. Seismic air-gun surveys also have serious consequences for the health of commercial marine fisheries. Seismic air-gun blasting has been shown to dramatically lower the catch rates of commercially valuable species such as cod, haddock, and black drum, by as much as 40 to 80 percent over thousands of square kilometers, leading upset fishermen from around the world to demand compensation from the oil and gas industry for their catch losses. Other impacts on commercially harvested fishes included habitat abandonment, reduced reproductive rates, internal body injuries, and hearing loss or disorientation.
A scientific study from 2017 concluded that seismic air-gun surveys also have detrimental effects on the tiniest forms of marine life – zooplankton – that form the basis of the entire marine food web. Researchers towed plankton nets through a bay on the coast of Tasmania both before and after firing only one underwater air gun, and discovered that the abundance of zooplankton collected declined by more than 60 percent within just one hour of noise exposure. In addition, the single air-gun blast caused a two to threefold increase in dead zooplankton counted within a 24-hour period after noise exposure, as compared to zooplankton collected in a control group.
Another significant finding was that sonar measurements conducted on-site in the aftermath of the study indicated that overall zooplankton abundance decreased as far away as one kilometer from the initial source of the blasts. These results clearly show that the seismic process, the first step in gas and oil exploration, poses not only undeniable threats to marine mammals and fishes, but also to the entire marine ecosystem starting at the very base of the food web. The results from this study were timely, coming out just weeks after the National Marine Fisheries department of the National Oceanic and Atmospheric Administration (NOAA) approved permits allowing for seismic blasting surveys along the Atlantic seaboard in the search for natural gases and pockets of hydrocarbons.
If such disruptive and destructive activities are allowed to occur devoid of significant governmental regulations, the populations of zooplankton could be reduced, or at worst, decimated, by such tactics.
Fortunately, there is promise for reducing the amount the amount, volume, and duration of underwater noise pollution in the world’s oceans, as there are practical and feasible solutions to this dire global environmental problem. Regarding the underwater sounds of large commercial trans-oceanic shipping vessels, one solution is designing new ships and/or retrofitting older ones, with more efficient propellers that reduce cavitation while cruising the oceans. This would lead to a reduction in fuel usage and vessel maintenance costs to the shipping companies themselves, while also significantly reducing the volume of underwater shipping noise.
In addition to propellers and ship hull structures, the vessels’ speed also plays as role in overall noise production. By slowing down while cruising the high seas or pulling into port, the vessels would be able to reduce noise production. This outcome would improve the companies’ bottom lines while actively reducing the amount of disruptive and harmful ocean noise they produce.
In attempts to dramatically reduce the harmful impacts of air-gun blasting, the most effective approach is to address the site location, volume intensity, and duration of seismic surveys. Just one major company/agency should conduct the most thorough survey possible and then share the findings with other companies to reduce impact while having the same results. Seismic blasting surveys should only be conducted in areas and at times when densities of whale, zooplankton swarms, or schooling fish are known to be low. The number of seismic surveys conducted per year per region should be limited, and the development, promotion, and implementation of less harmful technological alternatives must be supported.
Perhaps most importantly, governments must take a much more pro-active role in overseeing regulation and limitation of anthropogenic sources of marine noise pollution. This can be achieved in several important ways, according to reports by the National Resource Defense Council (NDRC) and International Fund for Animal Welfare:
- Federal regulatory agencies (e.g. NOAA, Bureau of Ocean Energy Management, Mineral Management Service) should require the use of eco-friendly technology and methods that have the smallest environmental footprint.
- Congress should require the implementation and enforcement of ship-quieting guidelines on all U.S.-registered commercial vessels, as well as provide monetary incentives/tax benefits for all new or existing privately owned commercial and recreational vessels that agree to install ship-quieting technologies and follow guidelines.
- The Administration (current and those to follow) should establish a program in order to advise and aid port authorities in commercial and recreational ship noise management plans.
- Congress should strengthen the environmental review of seismic surveys conducted in the waters of the Outer Continental Shelf.
- Both Congress and federal agencies should authorize and allocate funding the research and development of lower-impact technologies for underwater benthic exploration, and set 5-year and 10-year benchmarks for their development and application.
Overall, it is clear that immediate action needs to be taken to reduce the amount and volume of underwater noises inundating the submerged world. If you the reader are concerned about the impact of underwater sound pollution on marine life, then you can contact your state or federal representatives and tell them, urging them to take further actions to help solve this problem. The future of the ocean realm and its inhabitants need all the help they can get.