[CINC] Dolphin sonar research

[Victor Cox]

Fellow Naturalists,

FYI: Yet another reason to marvel at, and wonder about, at least one species
of dolphin that may be seen in the Channel.
Enjoy,
Vic

 Dolphins use double sonar

Lund, Sweden (SPX) Jun 09, 2011

Dolphins and porpoises use echolocation for hunting and orientation. By
sending out high-frequency sound, known as ultrasound, dolphins can use the
echoes to determine what type of object the sound beam has hit. Researchers
from Sweden and the US have now discovered that dolphins can generate two
sound beam projections simultaneously.

"The beam projections have different frequencies and can be sent in
different directions. The advantage is probably that the dolphin can locate
the object more precisely", says Josefin Starkhammar, a newly examined
doctor in Electrical Measurements at Lund University, who also holds a
Master's degree in Engineering Physics.

The study, which was carried out together with scientists from San Diego,
was published in the latest issue of the journal Biology Letters. The
co-authors of the article were Patrick W. Moore, Lois Talmadge and Dorian S.
Houser, who work at the National Marine Mammal Foundation in the USA.

"The findings add fuel to an already fierce debate in the research community
on how the echolocation sound is produced", says Josefin Starkhammar.

Dr Starkhammar's own guess is that the two sound projections come from the
two different sound-producing organs, the existence of which is well known,
but it was believed that only one was active during echolocation. She
stresses that more research is needed. For example, the two projections
could also be explained by complicated reflections in the head of the
dolphin, where the sound is formed.

"It is also somewhat remarkable that this has only been discovered now.
Research has been carried out on dolphins and echolocation since the 1960s",
says Josefin Starkhammar.

One explanation as to why the discovery has taken so long is that this
research requires recently developed and quite advanced measuring equipment
and signal processing techniques. In addition, until now it has mostly been
biologists who have conducted research on dolphins, and their expertise is
often not in this specific area of technology.

Furthermore, the research requires dolphins trained to answer scientific
questions! The combination of marine biologists and engineers is ideal, in
Josefin Starkhammar's view.

To help her she has developed a device with 47 hydrophones (microphones for
use in water).

"It is currently one of the best devices in the world for capturing
dolphins' ultrasound in water", says Josefin Starkhammar, who has spent a
lot of time testing and developing the equipment, including at Kolmarden
Wildlife Park, where one of her supervisors works. There she has also
conducted other studies on dolphins and their echolocation.

Bats also use echolocation and there are a few species of shrew and some
cave-dwelling birds which use a simpler form of the method. Even humans have
developed devices that use echolocation and ultrasound technology.

"However, dolphins' echolocation is in many ways much more sophisticated.
Evolution has had the possibility to hone it over millions of years.
Therefore, we humans have a lot to learn from dolphins. What is more, the
knowledge could be important in finding ways to protect dolphins, for
example, from noise disturbance", says Josefin Starkhammar.