High levels of background noise, mainly due to ships, have reduced the
ability of critically endangered North Atlantic right whales to
communicate with each other by about two-thirds, reports a NOAA-led
paper published in Conservation
Biology.
From 2007 until 2010, scientists from Stellwagen Bank National Marine
Sanctuary, Cornell Lab of Ornithology, NOAA Fisheries Northeast
Fisheries Science Center, and Marine Acoustics Inc. used an array of
acoustic recorders to monitor noise levels, measure levels of sound
associated with vessels, and to record distinctive sounds made by
multiple species of endangered baleen whales, including “up-calls” made
by right whales to maintain contact with each other.
NOAA Fisheries Northeast Fisheries Science Center documented more than
22,000 right whale contact calls as part of the study during April 2008,
and software developed by Cornell and Marine Acoustics Inc. of
Arlington, Va., aided in modeling ship noise propagation throughout the
study area.
Vessel-tracking data from the U.S. Coast Guard’s Automatic
Identification System was used to calculate noise from vessels inside
and outside the sanctuary. By further comparing noise levels from
commercial ships today with historically lower noise conditions nearly a
half-century ago, the authors estimate that right whales have lost, on
average, 63 to 67 percent of their communication space in the sanctuary
and surrounding waters.
“A good analogy would be a visually impaired person, who relies on
hearing to move safely within their community, which is located near a
noisy airport,” said Leila Hatch, Ph.D., NOAA’s Stellwagen Bank National
Marine Sanctuary marine ecologist and lead author of the paper. “Large
whales, such as right whales, rely on their ability to hear far more
than their ability to see. Chronic noise is likely reducing their
opportunities to gather and share vital information that helps them find
food and mates, navigate, avoid predators and take care of their young.”
North Atlantic right whales, which live along North America’s east coast
from Nova Scotia to Florida, are one of the world’s rarest large animals
and are on the brink of extinction. Recent estimates put the population
of North Atlantic right whales at approximately 350 to 550 animals.
“We had already shown that the noise from an individual ship could make
it nearly impossible for a right whale to be heard by other whales,”
said Christopher Clark, Ph.D., director of Cornell’s bioacoustics
research program and a co-author of the work. “What we’ve shown here is
that in today’s ocean off Boston, compared to 40 or 50 years ago, the
cumulative noise from all the shipping traffic is making it difficult
for all the right whales in the area to hear each other most of the
time, not just once in a while. Basically, the whales off Boston now
find themselves living in a world full of our acoustic smog.”
The authors suggest that the impacts of chronic and wide-ranging noise
should be incorporated into comprehensive plans that seek to manage the
cumulative effects of offshore human activities on marine species and
their habitats.
“We are starting to quantify the implication of chronic, human-created
ocean noise for marine animals,” said Holly Bamford, deputy assistant
administrator of the National Ocean Service. “Now, we need to ask how we
can adapt our management tools to better address these problems.”
