[OANNES Foro] New research teases apart complex effects of naval sonar on whales

[Mario Cabrejos]

New research teases apart complex effects of naval sonar on whales

by  <https://news.mongabay.com/by/ongabay-com/> Mongabay.com 

28 March 2019

https://news.mongabay.com/2019/03/new-research-teases-apart-complex-effects-
of-naval-sonar-on-whales/

Whales can behave quite differently in response to sonar depending on where
they live and what they're doing, new research has found.

The pair of studies, on different species and in different oceans, adds to
scientists' understanding of how to protect whales from these sounds. Navies
use sonar to detect stealthy submarines, and researchers have linked sonar
training exercises to hearing loss, deadly mass strandings, and interference
with whale communication.

Most strategies to temper the effects of sonar use the volume of the noise
as a guide, Brandon Southall, a biologist at the University of California,
Santa Cruz, said in a
<https://www.eurekalert.org/pub_releases/2019-03/tcob-sdb022819.php>
statement. But loudness didn't turn out to be the best predictor of blue
whales' (Balaenoptera musculus) responses to a series of sonar blasts in
<http://jeb.biologists.org/content/222/5/jeb190637.abstract> research
published March 4 in the Journal of Experimental Biology.

"Some whales responded when the sound was barely audible, while others
seemingly ignored it and kept feeding at quite loud levels," said Southall,
the paper's lead author.

A separate study, on northern bottlenose whales (Hyperoodon ampullatus) in
the Greenland Sea, found that these beaked whales - a group that's among the
most affected by sonar - changed their behavior, whether they were as close
as 0.8 kilometers (0.5 miles) to the source of the sonar or as far away as
28 kilometers (17 miles).

In that research, the scientists fixed data-gathering tags to 12 bottlenose
whales and used underwater microphones to listen in on what was happening
beneath the surface.

"All tagged whales stopped feeding, and individuals started swimming away
from the exposure site for several hours when a certain sound level was
reached, regardless of their proximity to the source," Patrick Miller, an
ecologist at the University of St. Andrews, said in a
<https://standrewsuni-newsroom.prgloo.com/news/distant-navy-sonar-affects-th
e-behaviour-of-whales> statement.

Miller and his colleagues published their
<https://royalsocietypublishing.org/doi/10.1098/rspb.2018.2592> work March
20 in the journal Proceedings of the Royal Society B.

Previous research has hinted that distant naval sonar wasn't as bothersome
to whales as the experimental pulses scientists use to investigate behavior
change. That finding didn't hold in the "pristine environment" where Miller
and his colleagues carried out their study.

"We used a sound source that is smaller than a typical operational naval
sonar," Miller said, "so the concern is that the distances at which animals
respond in the wild to real navy sonars may be significantly greater."

It's possible that these whales, with little exposure to naval sonar,
haven't figured out that distant sounds don't present the same danger as
ones nearby, Paul Wensveen, a co-author of the bottlenose whale study and a
University of Iceland biologist, said in the statement.

Off the coast of Southern California, where Southall and his fellow
researchers affixed tracking tags to 42 blue whales over five years, the
recorded behavioral responses to experimental sonar were mixed. To round out
their understanding of what was going on, several of the scientists used
echosounders to pinpoint swarms of the krill that are the staple of a blue
whale's diet.

Analysis of the data showed that, in general, whales feeding near the
surface continued unperturbed when buffeted with sonar. But more than half
of the tagged whales that were feeding deeper in the ocean abandoned their
dinners - at least until the sound of the sonar stopped. Once that happened,
most of the whales, which can grow to more than 30 meters (98 feet) and 200
metric tons (220 tons), set to feasting once again.

The researchers note that many factors could influence blue whales'
reactions to sonar. Still, Southall said, their findings offer a possible
avenue to alleviate the effects of naval sonar tests.

"Impacts could be minimized by reducing sonar disturbance during periods of
blue whale foraging on deep patches of krill in the military's main training
areas," he added.

Citations

Southall, B. L., DeRuiter, S. L., Friedlaender, A., Stimpert, A. K.,
Goldbogen, J. A., Hazen, E., . & Harris, C. M. (2019). Behavioral responses
of individual blue whales (Balaenoptera musculus) to mid-frequency military
sonar. Journal of Experimental Biology,222(5), jeb190637.

Wensveen, P. J., Isojunno, S., Hansen, R. R., von Benda-Beckmann, A. M.,
Kleivane, L., van IJsselmuide, S., . & Narazaki, T. (2019). Northern
bottlenose whales in a pristine environment respond strongly to close and
distant navy sonar signals.Proceedings of the Royal Society B, 286(1899),
20182592.

 



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