Boating is fun and relaxing, but even if you've never thought of it before, it is quite damaging for the hapless wildlife in the “Silent World” undersea. Since the year 2000, researchers have identified a myriad of environmental hazards associated with boating, which might have us re-appraising how we ride our boats in the water.
Sound is important for the survival of marine animals
Sound is the primary and the most efficient means of communication underwater. Most animals survive on the acoustic cues to hunt prey, find their mates and locate their homes, communicate, and warn each other of potential predators. On the other hand, sounds released by human activities and watercraft interfere with or mask the ability of marine animals to hear the natural or biotic sounds in the marine environment; thus, we call it oceanic noise pollution.
Over the past centennial, an increased rate of shipping, recreational boating, and deep-sea exploration along coasts and offshore environments has been fueled in parts by technology. And the sonorous noise from these activities travels a long way underwater.
Such noises adversely affect the abilities of marine animals to communicate with their mates, offspring, and other group members. There is no denying that this noise is masking not only the environmental cues vital for their survival but a concomitant change in ocean noise levels is also reported in several regions worldwide.
I will get over the impacts of boat noises on echolocation shortly. Let’s first familiarize ourselves with different sources of sound in the ocean or sea and how animals use these sounds to better understand the damage caused.
Sources of sounds in the marine environment
In a new study, Christine Erbe and her colleagues studied the effects of ship noise on marine animals. The team summarized different sources of sound undersea and the significance and impact of sound on marine organisms. Both biotic and abiotic sounds are present in the underwater environment.
Biotic sources include fish, invertebrates, marine mammals, and other marine organisms. These sounds are essential to communication and orientation, for finding mate and prey, and echolocation.
Abiotic sources, which provide important information about surrounding environments, can be categorized as natural background sound and anthropogenic sound.
Typical background sounds include the sound of sea waves crashing on the coast, currents moving over the reef, raindrops on the ocean surface, tides, oceanic turbulence, and the sound produced by seaquakes and submarine volcanoes eruptions.
Anthropogenic or man-made noises in the open ocean and coastal areas have significantly increased over the past few years. There is, again, both high-frequency and low-frequency noise. These noises vary in terms of frequencies and intensities. Long-term exposure to higher frequencies upto 20,000 Hz interferes with the hearing ability of killer whales, best known as orcas, to communicate and echolocate. The same goes for dolphins, porpoises, and other marine wildlife.
Two ways animals use sound underwater
Marine animals perceive sound, biotic or abiotic, in either of two ways;
1- Passive acoustics, in which an organism relies only on sounds produced by other animals and processes (or people). It doesn’t make any sound of its own.
2- Active acoustics, in which a pulse of sound is purposefully generated and received, much like a telephone.
The active acoustic system can be further defined as bistatic sonar (source and receiver are present at different places) and monostatic sonar (source and receiver are present at the same place). Much information can be learned about the object underwater, such as its composition, dimension, and distance, by analyzing the sounds received.
Humans and marine animals are using these acoustic systems for their benefits in the form of sonar and echolocation, and the collision of two is destroying life underwater!
Sonar (Sound Navigation And Ranging) is widely used to locate living organisms and objects underwater. Sonar systems also work on active and passive acoustics, as we have discussed before.
Similar to Sonar, echolocation is a phenomenon that is used by many terrestrial and aquatic animals to determine the location and characteristics of objects. In echolocation, animals emit various sounds such as clicks, croaks, or short sound waves to attract their mates and ward off potential invaders. These waves bounce back from solid objects and give the organisms an idea about their environment and information about the object’s distance based on the time an echo takes to return.
The echolocating animal doesn’t produce a second click until it hears from the first click. As the target gets closer to the echolocating animal, the click rate increases and ultimately sounds like a buzz. With this remarkable ability, dolphins can detect targets as small as the size of a golf ball at a distance of about a football field away. It is a fascinating phenomenon and has been used by humans as well in sonars in submarines.
Animals in aquatic settings use echolocation because their visibility is poor, so the dependence on acoustic vision is masked. But animals who use this technique underwater, like dolphins and toothed whales, including sperm whales, are under threat due to the sound made by the boats.
The impacts of signal masking by boat noise on echolocation in marine life
What makes the environmental impacts of boat noise on marine life particularly serious is that noise can travel longer distances in water than it would do on land (through the air). Secondly, the sounds from the boats cause what is called signal masking, and marine life is extremely sensitive to it.
Think of signal masking as the reduced ability to perceive and decode the information from the signal due to interference by another sound. And noise is anything other than the signal in question. So the noise is the primary reason for the signal masking in the air and underwater.
There are natural sources of the noise in the ocean, such as geo-seismic events, but now due to the overwhelming heavy traffic of the motorized boats and ships, such as recreational boats, jet skis, ferries, hovercraft, cruise ships, fishing or cargo vessels, naval ships, submarines, etc. noise has affected the vocal communication of marine animals in more profound ways.
“Vessel speed is the biggest predictor of such extravagant noise levels received by whales,” concluded scientists from the University of Washington and National Oceanic and Atmospheric Administration (NOAA) Fisheries. NOAA researchers are the first to examine how much noise from individual boats reaches the orca in the inland waters of Washington and British Columbia, where the endangered killer whales are a popular attraction for recreational and commercial whale-watching fleets.
Small watercraft produce noise of 130–160 dB, whereas large and powerful watercraft such as ferries, container ships, and icebreakers produce noise above 200 dB. However, a small watercraft traveling at high speeds can have more impact than a single, large, slow-moving vessel. There is evidence that a boat traveling with the speed of 5 knots will reduce acoustic communication within 50m by some 26 percent. This can also cause reproductive stress.
Species have taken to change in behavior to address this artificial interference which is causing a reduction in communication. While some whales make louder vocalizations to be heard, others simply move away from the noise polluted area, like the bottlenose dolphins in the cardigan bay alter their clicks when boats are present. We can say noise pollution is another form of habitat degradation.
It is worth noting that as many as 55 marine species have been observed to have suffered due to excessive exposure to the sound of varying frequencies. These include, but are not limited to, brown shrimp, bluefin tuna, cod, goldfish, grey whale, lobster, killer whale, minke whale, pygmy sperm whale, sperm whale, sea bass, squid, etc.
Whales like orcas are of main concern for marine scientists. “Orcas when they have decreased echolocation due to the noise of the ships and boats this leads to an inability to find their prey, that is chinook salmon,” says Scott Veirs of Beamreach Marine Sciences and Sustainability School, Washington. Now the salmon numbers have already decreased; with reduced echolocation, it is even harder to hunt. This decrease in food leads to the use of their excess blubber.
Now, this blubber is polluted by many man-made products, such as PCB, which might lead to other diseases and issues when released into their system. Also, the loud calls in a noisy environment take extra energy away from other biological activities such as feeding, resting, traveling, reproducing, etc.
Some animals can die merely hours after exposure to extreme underwater noise due to cetacean stranding, hemorrhages, damage to ears and internal organs during embryonic stages, disorientation or migration to newer places, and an overall panic response to the alien sounds.
Stranding or the beaching of marine animals like whales and giant squids has become a rather common environmental impact of oceanic noise pollution in Greece, Hawaii, Spain, and the coastal regions of the US. Although a survival strategy, migration isn’t promising at all. Most animals, shall they fail to adjust to the new environment, will become more vulnerable to predation.
Unlike other forms of pollution, light and noise pollution can be easily reduced and managed. The problem can be fixed by first addressing the situation. People need to know that their boats are killing whales and dolphins. The second part of the management requires that boat speeds should be reduced. In fact, the intensity of the noise can be halved by just dropping 6 knots.
Another thing that can be done is transfer the technology of quieter boats from the military. This will help hush the noise in the silent world and thus reduce the effect of noise pollution on marine animals.
Nida Riaz is a freelance blogger based in Pakistan. She started writing about her passion for the environment when the world came to a stop in early 2020.