December 11 2024
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Dolphins can shout underwater, but it is never loud enough
New York Times
last updated:
Jan 16,2023
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Mammals in the ocean swim through a
world of sound. But in recent decades, humans have been cranking up the volume,
blasting waters with noise from shipping, oil and gas exploration and military
operations. New research suggests that such anthropogenic noise may make it
harder for dolphins to communicate and work together.اضافة اعلان
When dolphins cooperated on a task in a
noisy environment, the animals were not so different from city dwellers on land
trying to be heard over a din of jackhammers and ambulance sirens. They yelled,
calling louder and longer, researchers reported last week in the journal
Current Biology.
“Even then, there’s a dramatic increase in
how often they fail to coordinate,” said Shane Gero, a whale biologist at
Carleton University in Ottawa, Ontario, who was not part of the work. The
effect of increasing noise was “remarkably clear”.
Scientists worked with a dolphin duo, males
named Delta and Reese, at an experimental lagoon at the Dolphin Research Center
in the Florida Keys. The pair were trained to swim to different spots in their
enclosure and push a button within one second of each other.
“They’ve always been the most motivated
animals. They were really excited about doing the task,” said Pernille
Sørensen, a biologist and doctoral candidate at the University of Bristol in
England. The dolphins talked to each other using whistles and often whistled
right before pressing the button, she said.
Sørensen’s team piped in sounds using
underwater speakers. Tags, stuck behind the animals’ blowholes, captured what
the dolphins heard and called to each other as well as their movements.
Communication is keyThrough 200 trials with five different
sound environments, the team observed how the dolphins changed their behavior
to compensate for loud noise. The cetaceans turned their bodies toward each
other and paid greater attention to each other’s location. At times, they
nearly doubled the length of their calls and amplified their whistles, in a
sense shouting, to be heard above cacophonies of white noise or a recording of
a pressure washer.
In noisy environments, “animals can’t talk to each other”. In the long run… such conditions could affect their food intake and ability to reproduce.
The noisier it got, the less success the
dolphins had with the task. At the loudest condition, they succeeded 62.5
percent of the time, simultaneously striking their buttons about 20 percent
less than under ambient sound levels.
“It was surprising to see how much the
success rate dropped,” Sørensen said.
Researchers in the past have observed wild
dolphins changing their behavior when boats are around. For instance,
scientists in Australian waters observed fewer dolphins, as the number of
dolphin-watching tourist boats increased. But no one had yet investigated how
anthropogenic sounds can muck up animals’ ability to cooperate.
“It’s usually really hard to do these kinds
of studies in the wild,” said Mauricio Cantor, a behavioral ecologist at Oregon
State University in Newport who was not part of the study. But the experimental
setup used by Sørensen’s team provided “clear evidence for the effect of
noise”, he said, because the researchers could control for most everything that
could interfere with their results.
When an ocean home becomes a hostile
environmentDolphins hunt together, using sound to
communicate, and find their way through echolocation. They also use sound to
stick together with their families and whistle to signal their presence to
peers, Gero said. In noisy environments, “animals can’t talk to each other”. In
the long run, Cantor said, such conditions could affect their food intake and
ability to reproduce.
There may already be portions of the oceans
that are not usable for these animals anymore, Gero said. Dolphins may migrate
from places where they cannot communicate successfully. This phenomenon may
already be occurring at major ports in places like Los Angeles or Boston, he
said.
Ships are one of the main contributors to
noisy ocean soundscapes, and in some spots, ships are slowed to protect
wildlife from noise pollution, Gero said. For instance, along parts of the
Pacific Coast from Washington state to Chile, boats are instructed to slow down
or alter course to reduce noise that could bother marine mammals.
“We’re absolutely impacting animals in this
way already,” Gero said. “The unfortunate reality is that, in some ways, this
story is 35 to 50 years late.”