massive noise map extending into the North Atlantic. The
scales – which show annual averages – range from red (115
decibels (dB) at the top) to orange and yellow, and then to
green and blue (40dB at the bottom).
In another study, researchers used underwater micro-phones
to measure the noise created by about 1,600 ships
as they passed through Haro Strait, in Washington state.
The two-year study found that the average intensity of
noise next to all the ships was 173 underwater dB, equiva-lent
to 111dB through the air – similar to the sound of a
loud rock concert. At a distance of around 1m, the noise
from an oil tanker was around 200dB and from a tug was
around 170dB.
Whales, the researchers found, would typically be
subjected to noise of about 60 to 90dB – around the level of
a lawnmower or a vacuum cleaner.
Measurements off the US west coast indicate that low
frequency noise levels – those that best reflect noise from
commercial shipping – are increasing by around 3dB every
10 years, representing a doubling of acoustic power at
those frequencies every decade.
It’s not just the decibels, however. Scientists say that
marine life is being disturbed by a ‘cocktail party effect’ of
noise from various sources, including oil drilling, dredg-ing,
and seismic surveys, which can travel for long
distances underwater.
An experiment conducted in the early 1990s showed
that sound emitted from Heard Island, near Australia, was
76 SUOMEN MERENKULKU J FINLANDS SJÖFART
picked up at sites in the northern and southern Atlantic and
Pacific Oceans as well as the Indian and Southern Oceans,
and sound from seismic airguns was recorded from more
than 4,000km (2,500 miles) away.
‘Being able to produce and detect sound is critically
important to many marine species, so changes to the
natural background soundscape may have more effects on
ecosystem health than previously thought,’ said NOAA
fisheries biologist Jason Gedamke.
Many marine species use sound to find prey, avoid
predators, locate mates and offspring, guide their naviga-tion
and locate habitat, and listen and communicate with
each other.
Dr Nathan Merchant, head of the CEFAS noise and
bioacoustics team, told the BBC that researchers are
looking into the many ways in which marine life is being
affected by noise.
‘We know that chronic stress in humans, for example, can
have long-term health effects, and we’re concerned for the
same reasons in long term health effects in seals and other
marine mammals,’ he added.
The International Maritime Organisation (IMO) has,
since the early 1980s, recognised the way that human health
can be damaged by noise onboard ships, with the SOLAS
Convention setting mandatory maximum noise level limits
for machinery spaces, control rooms, workshops, accommo-dation
and other spaces onboard.
But the IMO is now looking at ways to enhance existing
non-mandatory guidelines, introduced in 2014, which aim to
cut underwater noise from commercial shipping.
Efforts are concentrating on cutting noise caused by
propeller cavitation – the biggest source of sound from
shipping – as well as reducing the transmission of mechani-cal
noise through the ship’s hull though changes to hull
form, onboard machinery, and various operational and
maintenance recommendations such as hull cleaning.
Studies suggest that reducing ship speed can be espe-cially
effective in reducing noise. Researchers in Canada,
looking at the impact of noise on beluga and bowhead
whales and Arctic cod, found ‘substantial’ benefits could be
gained by cutting the speed of containerships and cruise-ships
from 25 knots to 15 knots.
The noise maps are also likely to lead to the creation of
new routeing schemes to avoid particularly sensitive sea
areas.
However, the IMO agreed last year that a lot more work is
required before tighter controls are introduced. Delegates at
the Marine Environment Protection Committee noted that
there are still ‘significant knowledge gaps, and that sound
levels in the marine environment and the contribution from
various sources was a complex issue, so setting future
targets for underwater sound levels emanating from ships
was premature and more research was needed – in particu-lar
on the measurement and reporting of underwater sound
radiating from ships’.
The work being carried out by the US NOAA could prove
crucial to this. In 2014, the agency established a network of
10 undersea listening stations around the US designed to
systematically measure ambient noise levels in the ocean.
This project is the first large-scale effort to monitor
long-term changes and trends in underwater sound and, the
agency says, will ‘help scientists understand what ambient
ocean sound levels are now, how they are changing over
time, and what impacts man-made noise could have on
marine life’. •
G Canada’s port of Vancouver has produced
a guide to reducing noise from ships.