Ocean uproar: saving marine life from a barrage of noise
April 10, 2019, Nature.com

“There is a political will to regulate underwater noise,”
says Jakob Tougaard, a bioscientist at Aarhus U. in Denmark.
Last Nov, the UN agreed on resolutions to conserve ocean
health that noted an “urgent need” for research & cooperation
to address the effects of anthropogenic underwater noise.
The EU has adopted legislation to achieve healthy marine
systems by 2020, including a provision to ensure that under-
water noise does not “adversely affect” marine life.
Shipping organizations are concerned, too: in 2014, the Int'l
Maritime Organization issued guidelines on reducing noise
from vessels.

But there’s still a gap in the science. Because noise is
so pervasive, it is hard to study the impact as it ramps up.
It isn’t clear whether marine systems can work around or
adapt to it — or whether it will drive crashes in already-
stressed populations. So researchers are becoming acoustic
prospectors, searching for quiet zones & noisy habitats in
efforts to chronicle what exactly happens when sound levels
change. Efforts range from natural experiments on the effects
of a plan to re-route shipping lanes in the Baltic Sea,
to investigating the impact of a trial scheme in Canada to
reduce ship speeds in coastal waters off Vancouver.

In the grand scheme of ocean ecosystem threats, climate
change might be a bigger issue — along with acidification
& pollution. But researchers worry that background noise
will be the straw that breaks endangered species’ backs.
“Two stressors together are more than just A plus B,” says
Lindy Weilgart, a biologist at Canada’s Dalhousie U. in
Halifax. “The negative effect is greater than the
sum of the parts.”

Far-from-silent world
====================
Decades ago, not much was known about ocean noise. When
Jacques Cousteau made a documentary about the ocean in 1956,
he called it The Silent World — a misnomer that researchers
today point to with much mirth. In reality, the ocean is a
noisy place: waves, marine life and rainfall create their
own din. A humpback whale can be as loud as an outboard
motor, Seger says.

Humanity has greatly added to the ocean soundscape. There
is no global map of ocean noise, but researchers agree that
ship traffic approx. doubled between 1950-2000, boosting
sound contributions by ~3 decibels/decade. That translates
to a doubling of noise intensity every 10 years (decibels
are calculated on a logarithmic scale). Sound travels
differently thru air from thru water, making it hard to
compare the two environments. But the blast of a seismic air
gun used to map the sea floor for oil & gas can be as loud
as a rocket launch or an underwater dynamite explosion;
ship engines & oil drilling can reach the roar of a rock
concert (see ‘A sea of sound’). Some of these sounds are
audible for hundreds of kilometres.

The most obvious sign of trouble came when masses of dead
beaked whales started showing up on beaches. Loud sounds seem
to trigger panic dives that cause a kind of decompression
sickness in the cetaceans, & haemorrhages in their brains
& hearts. In the 5 decades before 1950, researchers recorded
just 7 mass strandings; but from then to 2004, after the
intro of high-power sonar for naval ops, there were over 1201.
Studies show that exposure to loud noises can damage ears &
cause hearing loss in cetaceans. It can also affect inverte-
brates — by impairing the development of scallop larvae,
for example. In 2017, researchers reported that seismic-
survey blasts could scythe thru the water & kill zooplankton
over one kilometre away; the acoustic beam dispatches them
“like mowing the lawn”, says Rob Williams, co-founder of the cetacean-conservation group Oceans Initiative in Seattle.

Background noise also has an effect. Researchers got a rare
chance to study this in 2001, after the terrorist attacks
on NYC’s twin towers. Commercial transport ground to a halt,
& that dimmed the marine noisescape substantially. Rosalind
Rolland, director of ocean health at the Anderson Cabot Ctr
for Ocean Life in Boston, was conducting a long-running study
of faeces samples from right whales (Eubalaena glascialis),
& noticed a drop in stress-related metabolites. That was the
first biological evidence that exposure to low-frequency
ship noise was associated with chronic stress in cetaceans.

A swathe of other studies has shown that boat noise can
increase stress-hormone levels in creatures including fishes
& crabs, causing them to spend more time patrolling for
danger than caring for offspring, for example. In one study,
the survival rate of Ambon damselfish (Pomacentrus amboinensis)
on a reef dropped to less than half its previous level when
the animals were exposed to boat noise. Dolphins change their
tune: they whistle at a lower frequency, with less variation,
if the ambient noise is loud. Some humpback whales simply
stop singing. All this is likely to alter relationships
between species in as-yet-unknown ways, says Williams: louder
seas are surely changing who can effectively catch food,
find a mate or hide from predators.
----------------
Animation created from data gathered from recorders at
the bottom of Boston harbour shows the whistles and
clicks of whales (small dots) being drowned out by
ships (large dots) sailing in and out.
Credit: D. Ponirakis, L. Hatch and C. W. Clark
-------------
A rule of thumb suggested in 2016 by the US NOAA is that
pulses of sound above 160 dB cause marine mammals to change
their behaviour. For chronic, continuous, noise, that benchmark
is a lower 120 dB. The difficult question is whether this
noise is something that ecosystems and populations can
adapt to, or something more serious.

Perhaps the best evidence that background noise might be a
critical problem comes from data on killer whales (Orcinus
orca) off the Pacific coast of Canada. Researchers including
Williams reported that resident whales spent 18–25% less
time feeding when surrounded by boat noise than when bathed
in quiet. There are only 75 southern resident killer whales
remaining in this area, and they are already battling a
drastically lowered food supply, thanks to declining salmon
stocks, Williams says. “We’re not talking about a quality of
life issue; we’re talking about something with real impacts.”

The quiet-oceans experiments
=======================
In the face of such challenges, environmental scientist Jesse
Ausubel at NYC’s Rockefeller U., a decade ago proposed the
grand idea of an Int'l Quiet Ocean Experiment (IQOE). Ausubel
had previously co-founded ambitious projects including the
Census of Marine Life, a massive project that aimed to
catalogue all oceanic organisms. In 2011, he & others published
the idea of hushing the ocean to see what the absence of noise
allows.

Since quieting the entire ocean is infeasible, even for a
day, the idea was adapted to encompass smaller, more manageable
tasks. In 2015, the IQOE published its science plan, & it
now acts as an umbrella body dedicated to coordinating, but
not funding, marine noise research. One of its main goals is
to simply gather more data: last year, it convinced the
Global Ocean Observing System, a lauded UN project that
coordinates the satellites, buoys & research vessels that
monitor the ocean, to add noise to its list of essential
variables, alongside other fundamentals such as temperature.

Among the projects that the IQOE endorses are Seger’s work
in Colombia, and a natural experiment in the Baltic. Sweden
& Norway have taken the unusual decision to divide a main
shipping lane thru the Kattegat Sea (between Denmark & Sweden)
into two, starting next year, to make the busy route safer
to navigate. Tougaard and colleagues plan to deploy 10–20
hydrophones throughout the region this summer to help document
the effect of shifting the paths of some 80,000 ships per
year. Such data will be useful in other regions, too, Tougaard
says, including a shipping lane that crosses near some
sandbanks used by a critically endangered population of
Baltic Sea harbour porpoises (Phocoena phocoena) for breeding.
“If there’s an impact, it might make sense to move that
shipping lane,” he says. “It will be a longer route, which
costs money & means more CO2 coming out of the chimney.
So we have to be certain.”

The Arctic is another area of opportunity for study, says
Seger. As the ice melts & shipping lanes open, anthropogenic
noise could become a major stressor for species facing
multiple rapid changes. Ship traffic in the region increased
by 75% from 2005-2017, & some researchers have recommended
moving shipping lanes to avoid sensitive species.

Williams thinks he has found another spot for controlled
studies. In 2016, he learnt about a Hindu tradition called
Nyepi, a day of silence that takes place in Bali in early
March. It is rigorously observed: all shops, airports and
shipping and fishing shut down, and tourists are gently
led off the beach back into their hotel rooms. Williams saw
this as a unique opportunity: “No one in the world shuts
up for a day,” he says. In 2017, he went to Bali and put
six hydrophones in the water to measure the effect of the
silence. “The drop was in the order of 6–9 dB. About the
same off New York and Boston after 9/11,” he says. “This
was extraordinary.” The next step, says Williams, is to
investigate what the corals and fishes do in response to
the silence although as yet he has no specific plans or
funding to go back.

Keeping quiet
============
As with climate change, there’s enough evidence for the
harm of marine noise to move forward with action, but debate
lingers over the scope & urgency of the problem. Fortunately,
noise is easier & quicker to reduce than is, say, ocean
acidification or fossil-fuel use, says Seger. “It’s redesign-
ing propellers & re-routing shipping lanes,” she says.
“We can make tangible changes.”

One experiment has tested some of those changes in the
Haro Straits around the SE tip of Canada’s Vancouver Island,
where the clan of killer whales that Williams studied spend
time each year. From Aug-Oct 2017, many of the container
ships & merchant freighters travelling thru the straits
voluntarily slowed to 11 knots (nautical mph) from speeds
as high as 18 knots. That added half an hour to their journey,
but reduced the thrum of their engines. The ships were
responding to a request by the port’s Enhancing Cetacean
Habitat & Observation (ECHO) Program, which conducted a 2nd
trial last year. For some ships, dropping by just 3 knots
cut noise intensity in half.

When ECHO monitored a spot important for killer whales,
noise levels wobbled between 75 dB & 140 dB both before &
during the slowdown, depending on the weather, wildlife &
passing ships. But during the 2017 slowdown, the noise
dropped by a median of 1.2 dB — a 24% reduction in sound
intensity. The trial wasn’t designed to study whale behaviour,
but models predict that this drop in noise should reduce by
about 10% the time that the waters are clogged with
befuddling noise (for these whales, estimated to be levels
above 110 dB), giving the whales a better chance of filling
their bellies. The full 2018 results haven’t yet been released.

One of Williams’s studies showed that in a modern fleet of
over 1,500 ships, half the noise came from just 15% of vessels,
so targeting the worst offenders could go a long way. “That
means we do not need draconian fleet-wide regulation to get
us to our conservation targets,” says Williams. But retro-
fitting a ship with noise control can be expensive, & all
calls to hush ships have so far been voluntary. In 2017, the
Vancouver port authority started offering discounted rates
for quieter ships, making Canada the first country in the
world to host a financial incentive to reduce marine noise.
“In my view, Port of Vancouver is years ahead of the rest of
the world,” says Williams. But so far, uptake is limited: in
2017, only 34 of roughly 3,000 ships visiting the area took
advantage of the noise discounts.

Meanwhile, acoustic prospectors are helping to identify other
areas where noise might beneficially be reduced. Williams
has mapped out a hotspot where ambient noise overlaps with
porpoise populations off the coast of Haida Gwaii — a sparsely

populated archipelago off the coast of British Columbia
sometimes called the ‘Galapagos of the north’. Similar work
has looked at noise pollution in the Mediterranean. Such work
can also pinpoint areas that are both frequented by wildlife
& still quiet — prime areas, Williams argues, for preservation.

Existing conservation mechanisms, such as Marine Protected
Areas (MPAs), might be natural places to introduce the idea of
limiting noise, Williams argues. It would be a coup, he says,
for someone to host the world’s first official “quiet MPA”.

The good news is that noise pollution can be tackled extremely
rapidly; there are known solutions & effective ways to mitigate
the risk. Weilgart says that the air guns typically used in
seismic surveys could be replaced with an underwater vibrator
that creates a smaller sound footprint & a lower peak pressure,
reducing the chance of injury to marine life. When regulators
set limits on the noise of pile driving for offshore wind
farms in Germany, Weilgart says, the industry quickly took up
quieter methods, such as wrapping piles in a curtain of
bubbles to absorb the sound. Companies are now coming up with
ways of sinking the piles rather than hammering them in, she adds.

Vessels can be made quieter by elevating engines off the
ship floor, or using propellers designed to reduce cavitation
— the creation of tiny bubbles, which pop loudly when they
explode. Modern communication methods can help ships to
approach ports slowly, adds Tougaard, rather than speeding
in only to idle just outside until a docking point becomes
available. Many cruise ships now use electric motors to drive
their propellers, mainly to reduce noise levels for their
paying customers, but also to the benefit of marine life.

Fortunately, Weilgart says, most ship-quieting moves go hand-
in-hand with improving fuel efficiency. “I’m very solutions
focused,” she says. “We just need to quiet the bloody noise.”

https://www.nature.com/articles/d41586-019-01098-6

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