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In 1970, an album titled ‘Songs of the Humpback Whale’ was released
with 35 minutes of sound recordings of these whales. The album was
nothing like anything people had heard before and it went on to sell 30
million copies worldwide. The operasque sounds created by the whales,
dolphins and most other cetaceans continue to fascinate scientists even
today with many recordings revealing the extreme frequencies these
sounds can be emitted in. Scientists have also found through several
studies that the sounds are not just for social interactions in the
underwater world. They are also fundamental cues for feeding,
navigation, and communication in the ocean.

What happens then if a mother whale is trying to teach the baby whale to
swim across a difficult waterway and suddenly the baby cannot hear the
mother’s cues because there are multiple other sounds coming its way?
What if the other distractions are so loud and unfamiliar that the baby
whale actually gets alarmed on hearing them and gets lost? Increased
noise from shipping traffic, motorized fishing vessels, underwater oil and
gas exploration, offshore construction and other human activities are
creating exactly this kind of ruckus for the whales and other marine
species that can leave them confused and disoriented. And because the
physics of sound travel underwater is so different from the way it travels
in air, there are multiple levels at which such noise pollution can interact
and affect the lives of all marine animals.

Francis Juanes, an ecologist at the University of Victoria in Canada and
Arlos Duarte, a marine ecologist at the Red Sea Research Center in Saudi
Arabia recently analysed decades of data sets and studies of the effects of
noise pollution on marine creatures. They found that human-made
sounds are impacting all marine dwellers in a negative way – so much so
that some fish larvae are unable to find their habitats or homes.
Prof. Duarte says that while the importance of sounds has been studied
in detail in humpback whales, who are able to communicate through
thousands of miles using complicated songs, there is also evidence that
miniscule fish larvae ‘hear’ the call of their habitat and follow it to find home when they are drifting on the waves. Unfortunately, he says, that
call is no longer being heard.

“Imagine having to raise your kids in a place that’s noisy all the time. It’s
no wonder many marine animals are showing elevated and detectable
levels of stress due to noise,” said Joe Roman, a University of Vermont
marine ecologist.

The scientists found that fish and some invertebrates avoid certain areas
of the Red Sea where the frequency of ships travelling is high. They also
noted that the overall number of marine animals has declined by about
half since the 1970s. “In some parts of the ocean, there were fewer
animals singing and calling than in the past – those voices are gone,”
said Duarte.

The Sound Impact

There are several reasons why sound tends to become a greater stress for
aquatic animals than those living on land. Sound travels almost five
times faster through sea water than through air, and low frequencies can
travel hundreds of kilometres with little loss in energy. In addition to
this, the hearing range of marine mammals is far greater than their
vocalisation range as they rely on sound cues much more than visual
cues to avoid predators too. Also, because the whales and dolphins utilise
a wide band of acoustic frequencies – from low-frequency sounds down
to ~15 Hz used by Blue Whales to 120–150 kHz used by several species of
porpoises – the broad range can easily intersect with almost all sounds
introduced by humans in water. All this gives rise to conditions that can
be quite complex to maneuver for all kinds of animals be it tiny shrimps
or massive whales.

According to a 2018 study by Maritime Research Centre (MRC), Pune
ship movement in the Arabian Sea, Bay of Bengal and Indian Ocean led
to decibel (dB) levels increase in the seas from a maximum of 185-190dB
to 210dB over seven decades. In this period, the minimum noise levels
along major shipping routes too, had gone up to 110dB from 90-95dB.
The sources of these sounds included > 200dB: Sound from ships for
communication purposes or to detect any danger, 200-250dB: Seismic surveys airguns used to illuminate the sea bottom to understand the nature and detect presence of oil activity, and 100-150dB: Sounds of various machines that aid movement of large ships and vessels. The researcher warned that such sounds could not only lead to discomfort but also internal injuries, bleeding, haemorrhages, or even death among the marine animals.

A 2019 study noted another harsh effect of human sounds. Increased
ship traffic across the Ganga is stressing the river’s iconic dolphins –
India’s national aquatic animals – and changing the way they
communicate. For a mammal that’s almost blind, and relies heavily on
echolocation to communicate, feed and breed, this kind of stress can
easily spell the difference between life and death.

Turning the Volume Down

An interesting observation Juanes and Duarte additionally made during
their study, was the effect of the global lockdown on the reduced human-
made sound levels and thereby the activity of marine creatures. They
found that when 60% of people were under lockdown in 2020, there was
20% reduction in the human noises created underwater. Almost
immediately, large marine mammals were seen around coastlines and
areas of the seas where they had not been observed for decades. The
scientists say this showed how easy it is to set the volume right for
marine animals to live alongside all the development noises humans are
creating.

The scientists strongly feel that when it comes to the various
environmental challenges like climate change and plastic pollution that
are also impacting ocean health, noise pollution is often given less
attention whereas tackling this marine “anthrophony” was the “low-
hanging fruit” of ocean health.

“If we look at climate change and plastic
pollution, it’s a long and painful path to recovery,” Prof Duarte said. “But
the moment we turn the volume down, the response of marine life is
instantaneous and amazing.”

While the whales are fish cannot have a mute button or ear plug to
muffle the alien human noises, the responsibility to lower the marine
‘loudspeakers’ for our marine neighbours lies with us and is not difficult
to execute.

Atula Gupta

Original publication: Deccan Herald

Published on: 10 March, 2021

Link: Underwater Under Seige

Featured image courtesy Pixabay , Image 1, Image 2