Among the mounting evidence that anthropogenic noise has palpable
negative impacts on marine life, new research is demonstrating that noise in the marine environment not only impairs marine
mammals, but fish, cephalopods, and invertebrates as well, all while the world’s oceans are getting noisier. Analysis
by Scripps Institution of Oceanography of declassified Navy documents in 2006 concluded that underwater sound levels off the
coast of southern California increased three decibels per decade between 1964 and 2004.
While Navy sonar and its impact on marine mammals
has received much attention over the past decade or more, there is increased awareness of commercial shipping’s contribution
to rising ocean noise levels, with vessel builders, owners, and operators—along with their consultants—continuing
to develop and implement methods of modeling, measuring, and mitigating underwater radiated noise (URN) from ship propulsion
“Most of the noise ships produce is at low frequencies (roughly 20–500 Hz),”
according to the University of Rhode Island. “In the frequency range of roughly 500–100,000 Hz, however, ambient
noise is mostly due to breaking waves, rather than shipping. At low frequencies the background sound level in many places
in the ocean is dominated by noise from distant ships, even when there is no nearby ship.”
The Ship Operations Cooperative Program (SOCP),
a non-profit organization of maritime industry professionals, examined the issue at its latest meeting earlier this month,
where Jason Gedamke, director of NOAA’s Ocean Acoustics program, provided background and the current picture. Also at the meeting, Yanran Wang, senior engineer at DNV GL, explained her organization’s
SILENT Class Notations, voluntary standards for URN emissions from vessels.
Jesse Spence, president of Noise Control Engineering, LLC, described
how reductions in noise of 3-5 dB for individual ships can be achieved through measures taken during the design, engineering,
manufacturing, and installation stages—something Gedamke said would signal a great improvement if applied across the
fleet. Decreasing vessel speed also has the potential to reduce noise. “Depending
on how much you reduce speed, you could achieve a 3-5 dB reduction in noise, or more; it just depends on how much you reduce
your speed,” said Spence.
“My big picture takeaway is that noise is becoming a greater concern, and shipping vessels (and other vessels,
including ferries, tugs, and other workboats) will likely be required to meet underwater noise specifications in the future,”
Spence told NRR. “However, the ‘line in the sand’ will be tough to identify since there are so many different
species out there with differing sensitivities to noise.
“It may be more practical to approach the question of noise requirements or limits,
reducing noise not from a biological perspective but from an engineering perspective. We know today how to reduce noise from
ships, so it would be possible to identify realistic targets for ships. We probably cannot go back to noise levels that existed
before motorized ships, but we can limit the increase in noise and potentially reduce noise worldwide.”