It’s a racket! The lively, un-quiet ocean of clicks, whistles, rumbles and more…

Flukes for Thought by MareCet
12 min readMay 31, 2021

by Dhivya Nair, Saliza Bono & Louisa Ponnampalam, Ph.D.

Note: This article is best read with your volume up and earphones on! Read on, you’ll see why.

Bright and early on yet another survey day, the MareCet team head down to the jetty, load up the boat with equipment and they are all set to go. The observers take their positions at the bow of the boat as the boat skipper starts the engine and the volunteers look ahead, eager at the prospect of seeing more cetaceans today. As the boat begins to head out into the survey site, Saliza Bono, MareCet’s bioacoustician, quickly gets to work.

Time is crucial here, as she needs to have all of her equipment set up before a pod of dolphins are encountered. She is hoping to record the sounds produced by Indo-Pacific humpback dolphins and Irrawaddy dolphins today. In a frantic rush of coordinating volunteers and connecting wires to metal poles, and securing hydrophones (underwater microphones used to record sound) to lead weights, the device is set up as the boat speeds ahead.

MareCet’s bioacoustician Saliza Bono and Kovin, a volunteer, securing the hydrophones’ cables to lead weights

When the first Indo-Pacific humpback dolphins of the day are encountered, the boat slowly approaches the pod and stops at a good distance away. The observers immediately begin taking pictures and the rest of the team observe the dolphins, taking note of the behaviours on display. Saliza must now quickly set up the speakers and amplifiers, which were kept safely away during search effort to prevent them from getting wet with salty sea water. In what seems like a panicked rush, she now has 10 minutes to quickly prepare the devices and coordinate the volunteers on either side of the boat, making sure the cables aren’t tangled, and that everyone and everything is placed in the right position. This 10-minute buffer is to ensure the dolphins aren’t exhibiting behaviours that indicate they may be too uncomfortable with our presence. When ready, the hydrophones are deployed off both sides of the boat and the recording begins.

Saliza sat amongst volunteers Tâm and Qin Ling, who are holding the hydrophones as she records acoustic data

A few metres below the surface, the hydrophones start recording sounds of the underwater world. For those who may be unfamiliar with the ocean, picturing what sounds can be heard if you were to stick your head in the water may be quite different to what the hydrophones actually pick up. It’s not just the sounds of bubbles and waves like you hear on ambience soundtracks of ocean sounds, or even the sound you hear if you bring a seashell to your ear. In contrast, the ocean is actually quite a rackety environment.

First there are sounds from physical processes, encompassing events such as underwater volcanic eruptions and earthquakes, rain and waves breaking. Then of course, the sounds of the animal world, from grunting fish on a reef, to toadfish calling out for mates, and our personal favourites, the vocal whales and dolphins. Not to forget the man-made sounds, ranging from naval sonar ships, seismic exploration vessels, cargo vessels and fishing boats, to name just a few.

Sound of a volcano erupting underwater
A chorus of grunting fish
Blasts from a seismic air gun during a seismic survey
Clicks and whistles of bottlenose dolphins

As Saliza records, the audio speakers reveal the sounds below. The ubiquitous sound of snapping shrimps is easily heard. And off in the distance, a boat passes by, in which the hydrophones pick up as well. Saliza listens keenly, waiting to see if the dolphins vocalize. Some time passes on before she yells “Click!….Click!……..Whistle!”, indicating the noises the dolphins are making. All this is noted down along with the time and the behaviours that the dolphins are exhibiting visually.

Saliza, recording data as the speakers play the sounds being recorded. She is keeping her ears peeled for any dolphins’ clicks and whistles as well as the sounds of boat engines

But sometimes, it isn’t as clear that the dolphins have vocalized! Such is especially so when there are so many other sounds occurring above the water; from the waves lapping against the boat, team members yelling out data to be recorded or the low hum of the boat’s engines. In this case, the extra pairs of ears from the rest of the team are incredibly helpful. One other challenge that Saliza faces during a recording session is to ensure no trash entangles the very expensive equipment, which might cause damage to it or undermine the quality of the recording.

Communication in the deep blue
Living in an environment where light and visibility can be limited, sound and hearing capabilities play a large and important role for marine mammals. They use sound not only to communicate with one another, but also to hunt prey and navigate the vast oceans. Marine mammals have evolved the ability to use sound as an adaptation to living underwater, especially in various species that have much reduced vision due to their evolutionary history.

Baleen whales for instance, are able to produce “songs” that help them communicate with one another. These complex arrangements of song can vary between pods, and some species even have their own dialects. Toothed whales like dolphins and porpoises, on the other hand (or should we say flipper), use echolocation, which can be described as an in-built sonar system. Sound waves from clicks channeled via a dolphin’s melon out towards a solid surface are reflected back to the animal, allowing it to gauge and make decisions on distances, type or source of the object(s). That’s almost akin to painting a mental image of what the environment around them looks like.

Sound also plays a part in a cetacean’s social ecology in aspects such as pod structure, mother-calf pairings and the ability to find a mate across the oceans. So, it’s arguable that sound plays a vital role in the survival of these highly social animals. But what happens when that line of communication is broken and it becomes difficult to hear one another?

An audible threat
Noise pollution — defined as sound that is loud, unpleasant and usually unwanted, isn’t a new term or problem. That said, noise pollution isn’t an issue at the forefront of our minds as it isn’t something we can see. With maritime transportation and activities gaining more importance all over the world, we have neglected to think about just how much unnatural sounds we are introducing into our ocean ecosystems.

But is it really that big a deal when compared to issues like plastic pollution or overfishing? Well for animals living in the ocean, noise is yet another stressor to their already threatened survival.

Container ships, for example, make sounds the equivalent of 130 decibels in the atmosphere. For comparison, that’s in range of what a jet engine would sound like and it is also the threshold limit for auditory pain. Noise is obtrusive, uninvited and stressful. But that’s really an understatement. Underwater, sound travels faster than it does in air which means it also travels a further distance. Construction noises you hear from your neighbour’s next door could probably be heard in a different geographical state if we were underwater! That makes it that much harder to even try and escape or avoid the noise.

Man-made sounds and the audio realm of marine mammals
The main culprit here are engines and propellers, as ocean-going vessels rely on them to cover vast distances and to move quickly and efficiently. With the addition of seismic air guns and sonars beaming out their own sound waves in search of fossil fuel resources embedded in the seafloor, the natural soundscape of the ocean is constantly tainted with the sound of the human species. So how does it directly impact our marine mammals?

A seismic exploration vessel, used to survey the ocean floors to locate sources of crude oil and gas. Source: Wikimedia Commons

For one, the additional noise contributes to what scientists call auditory masking, a phenomenon often described most similarly to yelling over loud music at a concert to find a friend. Masking occurs when one sound is ‘hidden’ by another louder sound. In this case, the whistle of a dolphin for example, being masked by a loud boat, which then forces the animal to alter the way they communicate. This includes producing sounds at higher frequencies to communicate or staying silent when a ship passes through.

A loud ship (the screeching, ringing noise) overpowering the sounds made by orcas (sounds like squeaky calls)

However, cetaceans need more energy to produce louder sounds; staying silent could lead to the accidental separation of mother and calf pairs, or dolphins from their pod. Even the inability to detect predators as well as other dangers now becomes an issue.

The problem doesn’t stop there. Scientists have also observed other behavioural changes in certain cetacean species which include a reduction in the time spent on important behaviours such as resting and socializing and short-term displacement from key habitat areas. Mass strandings have been linked specifically to military sonar exercises and necropsies (animal autopsy) done on stranded animals have also reported inner ear damage, suggesting acoustic trauma from exposure to loud noises.

A mass stranding of false killer whales in Western Australia. Source: Wikimedia Commons

Between this and every other stressor that marine mammals have to face, from entanglement to accidental plastic ingestion, if we don’t act soon, we are likely to see more species falling over the edge into the species extinction pool. But as with any problem, the key to finding solutions is to first understand the problem at hand.

Lessons from listening
The MareCet team members are no strangers to the loud sea surface sounds of boat engines and cruise ship horns blaring. But to really understand how marine mammals use sound, we’ve got to listen to what goes on beneath the water’s surface.

Back at the lab, Saliza goes over her recordings, which she then analyses. Much like finding a needle in a haystack, she searches through what’s called a spectrogram. Picking out the different sounds the animals made, this is essentially bioacoustics, a field that merges biology and acoustics.

Saliza working through and analyzing the spectrogram to pick out sounds that the dolphins have produced. She is looking out for sounds like clicks, whistles and grunts, to name a few

These findings allow us to understand why and when these animals are producing these sounds, and what behaviour may be exhibited when they vocalize. Saliza also tries to understand how boat noise impacts dolphin acoustic behaviour in our study site in northwestern Peninsular Malaysia. Are they reducing communication when a loud boat passes by or do the animals stay completely silent? Perhaps they are changing their acoustic frequency to be better heard by other dolphins? Is there any metabolic stress to these dolphins because of boat noise? These are some of the questions she is trying to answer. Here in Malaysia, there is still a large gap in knowledge with respect to the impacts of underwater noise to marine mammals.

Turn the volume down please!
Our research findings are often used to inform policies and guidelines for ocean issues. We need to make our oceans quieter, although this is easier said than done. It is our hope that MareCet’s bioacoustics research on cetaceans will aid in the process of helping to quieten key habitat areas of marine mammals in Malaysia.

So, is there something the public or industry can do to help curb underwater noise pollution? This proves to be difficult to answer, as there isn’t a one-size-fits-all solution to the problem. Further challenges arise as not many bioacoustical studies on marine mammals have been conducted here in Southeast Asia, which limits our understanding of the problems specific to waters close to home.

A tourist on a jet ski was observed speeding past this mother and calf pair of Indo-Pacific humpback dolphins repeatedly off Pantai Tengah, Langkawi, Malaysia, oblivious to the presence of the animals. This photo was taken by the MareCet team in February 2020

Guidelines do exist for ships and boats, which now include quieter propeller designs and the suggestions for regular maintenance of vessel parts. Other guidelines include slowing down or using alternative routes that reduce the risk of ship strikes with marine mammals. There are now even whale-watching tour operators using electric boats, offering whale watchers a unique experience that is not just quiet but less harmful to our ocean giants.

However, some of these solutions may not be as practical as it seems. For example, upgrading boats or constant maintenance for better soundproofing may incur large costs, and going slower may take up more time and fuel, making the trips inefficient.

On a personal level, not much can be done as those of us reading may not be captains of sea-going vessels, but staying informed is the best thing one can do. If you’re out on the water for recreational activities, try skipping the jet skis, and opt for the quieter kayaks or paddle boards. If you are someone who enjoys fishing, stay alert when boating and follow all speed limit zone rules.

A speed zone signage in Sarasota, Florida, USA, reminding boaters to maintain a no-wake speed as the area is home to manatees

What is really needed is an understanding of problems that involve these complex human-animal interactions, however the skills for that are severely insufficient. For example, Malaysia currently lacks regulations regarding the need for marine mammal observers out at sea or even just training for this specific job scope. Successfully carrying out a necropsy on a stranded animal here in Malaysia is also a job skill that is currently scarce, making it difficult to identify causes of death in a stranded animal. Some indicators of acoustic trauma that can be determined through a necropsy include an ear infection, or loss of hair cells and even lesions in the ear. Both these job skills could really help us identify problems relating to underwater noise pollution and acoustic trauma and how to go about solving it.

Political willpower needed
While underwater noise pollution is not exactly something the public at large can really have a hand in solving, unlike reducing plastic use or choosing more sustainable seafood options to help with overfishing, the actions required here more so rest on our governments and industry officials. Some countries have already begun to take action. One example includes Canada and their recent EcoAction Program that incentivizes reduced harbour fees for boats that implement noise reducing technology, encouraging for quieter waters. Over in New Zealand, marine mammal observers are made compulsory by the government to be onboard seismic survey vessels, allowing for better monitoring of the seismic surveys, which ultimately benefits marine mammals. Perhaps these are solutions that we here in Malaysia can implement to create a less bustling environment for our marine animals.

However, to implement these solutions, we must first have proper research and data to help drive the call to action, and that is what MareCet plans to do as we further delve into the rock, pop, classical and grunge soundtracks of our oceans, so to speak. Future research includes round-the-clock monitoring of our soundscapes to identify when and where these animals are most active and areas with the most overlaps of shipping and boating activities. Finding out which areas are most important to the animals will help us identify Important Marine Mammal Areas and areas that are in need of protection.

The MareCet team recording acoustic data and observing the behaviour of a group of Indo-Pacific humpback dolphins in Perlis, Malaysia; one of the deployed hydrophone’s cable is visible in the photograph

Research has shown that the blasts from seismic air guns can kill zooplankton. These organisms that form part of the important base of the marine food web may not necessarily be able to be observed with the naked eye. If tiny zooplankton are being impacted by underwater noise, then it must be that many other organisms along the entire food web are being affected as well. This is exactly why most refer to marine mammals as sentinels of the ocean. We see them, we are in awe of them, and hence the messaging and need to protect are usually that much stronger through these charismatic ocean mascots. Marine mammals are large and visible unlike zooplankton, for example, and are thus great indicators of the health of the oceans, including being “alarm systems” if the oceans have become too noisy.

The pandemic has given us a rare glimpse into how wildlife can flourish under the absence of humans. While the MareCet team is itching to head out into the field to see our favourite animals, the lockdown here in Malaysia has prevented us from collecting more bioacoustical data in the meantime. Even so, we can only hope that reduced human presence throughout Malaysia has provided some much needed rest and recovery for the marine mammals.



Flukes for Thought by MareCet

MareCet is an NGO dedicated to the research and conservation of marine mammals and their habitats in Malaysia.