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Quieting Marine Seismic Surveys
LESLEY EVANS OGDEN
Seismic sea surveys contribute significantly to underwater noise. Air guns
used in surveys can harm organisms,
such as whales, that communicate
acoustically. International efforts are
under way to find out what can be
done to reduce, mitigate, and possibly
replace noisy air gun technology.
Survey ships pull arrays of a dozen
or more air guns, releasing pressurized
air pulses into surface waters that penetrate up to 100 kilometers (km) into the
ocean floor. Bounced sound recorded by
ship-towed receivers provides a map of
subseafloor geology. Air guns are incredibly useful for oil and gas prospectors
but potentially hazardous for marine life.
Air gun pulses released from
60-­centimeter-long stainless steel cylinders are sharp, loud, and intense. Surveys
produce pulses almost continuously
every 10–20 seconds for days, weeks, or
even months. Their sounds are detectable 4000 km away. The gunshot-like
sound has a broadband frequency that is
potentially biologically harmful, explains
Dalhousie University marine mammal
acoustics scientist Lindy Weilgart.
Marine mammals such as fin whales
react to air gun noise as if to a predator, ex­plains Manuel Castellote, a marine
mammal acoustician with the National
Oceanic and Atmospheric Administra­
tion’s Seattle-based National Marine
Mammal Laboratory. Studying fin
whales in their rich Mediterranean
feeding and breeding habitat, he discovered that they moved and stayed
away from seismic survey areas until
2 weeks after the noise concluded.
Noise not only displaces marine
mammals but can also disrupt their
communication, reproduction, and
feeding and can cause stress effects,
hearing damage, and death, according to research. Similar effects, plus
lower catch rates, developmental
752 BioScience • August 2014 / Vol. 64 No. 8
abnormalities, and fatal strandings, are
being observed in fish and in squid
and other invertebrates.
Seismic surveyors often employ
ship-based marine mammal observers,
but whales’ infrequent surfacing and
deep-diving habits make them easy to
miss. Steve Chelminski, engineer, entrepreneur, and inventor of the air gun,
developed a prototype in the late 1960s.
“By the ‘80s, they were a big thing,” he
explains. Now, they’re standard practice.
Chelminski left the air gun business
over a decade ago and believes their
environmental impacts necessitate new
technologies. He is one of several competitors now prototyping and acquiring
intellectual property rights for an alternative: marine vibroseis (MV). The
land-based equivalent is already widely
used and largely replaced dynamite as a
seismic sound source decades ago.
John Young, former supervisor of
Exxon Mobil’s seismic research group,
now independent, says that there are two
ways to put energy into the ground: “a
large amount of energy in a short amount
of time or a small amount of energy over
a longer period of time.” The difference
between MV and air gun sound is “a
hum versus a bang,” he explains.
There is no way to adjust the bandwidth of air gun pulses. The result involves
wasted noise in the high-frequency spectrum, which is potentially harmful to
beaked whales and harbor porpoises but
useless for geophysical imaging.
In 2006, 13 oil and gas companies
created the E&P (for exploration and
production) Sound and Marine Life
Joint Industry Programme (JIP), subsequently sponsoring over $20 million
in research (www.soundandmarinelife.
org). Before 2006, air gun output was
understood from a geophysical but not
from a biological standpoint, explains
Young, the JIP chair.
Another JIP initiative coordinated by
Texas A&M University is investigating
MV. Its preliminary conclusion: MV
may cause fewer biological impacts
than air guns do, but further development and testing are needed.
In February 2013, the Bureau of
Ocean Energy Management (BOEM)
convened a multidisciplinary meeting
on quieting technologies. BOEM has
invested $50 million over two decades
to fund research on the distribution,
density, and life history of marine life
and on ocean noise biology. The United
Nations Environment Programme’s
Expert Workshop on Underwater Noise
and Its Impacts on Marine and Coastal
Biodiversity followed in February 2014.
“We don’t have a sense at this point
that MV would become an acrossthe-board replacement for air guns,”
says BOEM marine mammal expert Jill
Lewandowski. In some places, MV may
not work, explains Young, such as the
Gulf of Mexico’s shallow waters, “where
the bottom is like an acoustical sponge.”
Another proposed mitigation is
bubble curtains to constrain horizontal
spillage of sound. Others have proposed
passive acoustic monitoring—using
natural sounds such as earthquakes to
resolve an image—but image resolution, thus far, is insufficient.
“Exploration companies and oil companies are happy using air guns because
[air guns] work very well, and they
have huge, huge investment in them,”
says Chelminski. In July, the Obama
Administration gave the go-ahead to
oil and gas companies to use sonic
blasts in the Atlantic, despite acknowledging that 138,000 sea creatures could
be harmed, including nine of the last
500 North Atlantic right whales.
Lesley Evans Ogden is a freelance writer–
producer based in Vancouver, Canada, with
a passion for quirky science. Say hello at
lesleyevansogden.com or on Twitter @ljevanso.
doi:10.1093/biosci/biu097
http://bioscience.oxfordjournals.org