Low Frequency sound and Blue whales; Noise

From: Peter M Scheifele (acousticp2@juno.com)
Date: Sun Jan 06 2002 - 19:49:05 EST


Hi Sue,

Great sound questions! Here are a few superficial answers and if you'd
like to get more technical simply come back at me once again!

1. In general, we know that Blue Whales vocalise in a low
frequency band (as low as 2-20 Hz) and that they have been heard via the
Navy's SOSUS array half a globe away from one another. This, owing to
the low frequency (longer wavelength) and relatively high power, makes
sense. It not only works well in the underwater medium but in air as
well. Katie Payne has sent infrsonic signals that have been clearly
picked up by elephants over a mile away from the source (speakers atop a
van). Elephants may be thought of as essentially analogous to Blue
Whales in this regard. Some ground rodents are the same. I recently did
some research and a paper (in progress) regarding coyotes in which we
found that coyotes (at least in New England) howl at around 500 Hz,
which, incidentally, is not at their best frequency of hearing but well
below it. This is because they need to make the howl heard across their
(approximately) 4 X 4 mile home area through the trees and brush of the
forest. Once again, the low frequency is a triumphant tool. Please be
aware though, that aquatic ears and aerial ones, although similar in a
gross sense, are not the same and we do not know exactly what whales
hear, what constitutues loud ro threshold of pain.

Ahh, humans! Human speech generally occurs at between 2 - 8 kHz and at
varying levels. Before going on I must caution you that we measure sound
intensity in water using different reference levels (for decibel
measurements) than those measured in air. In water the units of measure
are dB re 1 uPa whereas in air the units are dB re 20 uPa (where dB = 10
log times pressure-squared / Pressure reference). The only way to
measure the sound using common type units would be as intensity in
Watts/meter-squared. Speech levels vary from individual to individual and
with respect to the background (intelligibility) but in a relatively
quiet environment at roughly 30 dB re 20 uPa. A human shout will likely
not travel more than a few meters underwater.

2. As for whether or not Blue Whales communicate over such long
distances, I feel the "jury is still out" on that. One has to ask "What
are they communicating about exactly?" To indicate the location of food
sources at such a long distance makes little sense since it would take so
long for the conspecific to reach the site that the food source would
likely be gone. Mating? Perhaps. However, in a short discussion with a
colleague of mine (Dr. Richard Sears) who is the authority on Blue Whales
we have begun to wonder whether or not Blue Whales navigate such long
distances at such depths in the face of some significant changes in
bottom topography that they might actually be using low frequency sound
as a means of "echolocating-for-navigation". If this is so, it would
have profound impacts on our present notions of pod distribution!

3. We have no clear cut evidence of hearing loss in marine mammals
of any type in the world oceans. We DO, however, have a good
understanding of the effects of noise on the mammalian ear (including
whales). In my own research in the St. Lawrence River Estuary in Canada,
I see evidence of potential hearing loss in heavily trafficed areas. The
only way to actually tell is to either have the animal undergo
audiometric testing or to image the ear (CT or MRI). Another colleague,
Dr. Darlene Ketten, has been doing this in studies of the cetacean ear
but little clear evidence has been found (excluding obvious barotauma).
It is a seroius concern though, especially to those of us who study
animal audiology.

We are all trying to get a handle on measuring these effects. Therein
lies the basis for my current research regarding the use of the
articulation index as a measure of hearing impairment (noise
interference) in the wild due to noise.

I hope this helps out!
Best Regards,
Peter

Peter M."Skip" Scheifele LCDR USN (Ret.)
Director of Bioacoustic Research
Animal Bioacoustics/Neuroanatomy
University of Connecticut

On Sun, 6 Jan 2002 10:59:22 -0800 "suer osenthal"
<suerosenthal@mminternet.com> writes:
Hi Peter:

Lots of sound questions:

1. I know blue whales can vocalize at 190 decibels and that their calls
can travel underwater for at least a thousand miles (Maybe farther?) But
how does this compare to other animals? How loud are humans and how loud
would a human shout travel underwater? Elephants?

2. What is the current thinking on whether blue whales communicate over
large distances? I.E. Even if we know their calls can travel long
distances, do we know they use this to communicate?

3. Finally, this is a rather broad question, but do scientists have
evidence of increased incidences of hearing loss in whales in heavily
trafficked oceans? I know that the theory is that increases in noise are
causing problems, but is it feasible to measure this?

Thank you,
Sue

Peter M."Skip" Scheifele LCDR USN (Ret.)
Hunters Road
Norwich, CT 06360



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