When sperm whales talk, UW researcher listens
(text adapted from a Oct. 29, 1999 UW press release)
Click on images for larger version.
A sperm whale wows passengers
aboard one of the boats from which Michael Dougherty collected data. The
UW researcher's method of acoustically identifying individual whales could
help biologists better understand and track the often elusive animals.
Below, a sperm whale dives beneath the Atlantic surface near Norway. Sperm
whales are among the deepest divers, descending thousands of meters and
remaining submerged as long as two hours.
(Photos by Michael Dougherty)
When sperm whales talk, Michael Dougherty listens.
Not only that, the University of Washington researcher and
electrical engineering doctoral student can recognize the
voice and tell you exactly which whale is
Dougherty has developed a method of acoustic
analysis that allows him to identify individual sperm whales
by the sounds they emit. The technology, which performed
with nearly 100 percent accuracy during a pilot study on a
limited number of whales, is believed to be the first of its
kind. It promises to help researchers better understand how
the leviathans interact as individuals and groups. It could
also be an efficient means of tracking the movements of one
of the ocean's more elusive mammals.
“It worked even better
than we had hoped during our pilot study,” Dougherty said.
“I think biologists who study the whales will find it very
useful after we develop it into a field-deployable
Sperm whales are probably best known to the
public through Herman Melville's novel Moby Dick. Just as
the whale in that story was hard to find, so can sperm whales
be difficult to keep tabs on in real life. When studying
other marine mammals, researchers typically use photography
to identify individuals, making distinctions on the basis of
such characteristics as marks and coloring or notches and
irregularities on dorsal fins or tails.
That method is less
effective with sperm whales.
“Whereas other species, such
as orcas, will swim together, sperm whales tend to spread
out,” Dougherty explained. “They may be a kilometer or more
apart. They're certainly in acoustic contact with one
another, but you can't keep track of who's where with just a
To compound the problem, sperm whales tend to be
out of sight more often than not. They are considered among
the deepest diving of the whales, descending thousands of
meters in a single dive and staying submerged for as long as
two hours at a time.
“They spend most of their time
underwater — about 83 percent of the time,” Dougherty said.
“When they come up, it might be a considerable distance from
where they went down and it's hard to get to them in time to
take a photo adequate for identification.” As a result,
much remains unknown about how sperm whales behave, he
“Most people don't understand how important it is in
studying animals to be able to identify individuals within
the group. Acoustic identification could allow us to do that
where it really couldn't be done before.”
reasons, an acoustic approach works particularly well in
identifying sperm whales, Dougherty said. One is that the
whales are extremely noisy.
“They emit short, loud sounds
called clicks about once per second,” he said, so researchers
have a continuous string of sounds to work with. “It's very
regular — it sounds almost like a clock ticking.”
addition, the clicks travel well in sea water, allowing
scientists to tune in from a distance and listen to more than
one whale at a time. Dougherty's process can differentiate
among individuals in a group.
“Acoustic identification can
work in all weather conditions, in darkness and at
considerable distance during the entire time that the whales
spend submerged and out of sight,” Dougherty said. “All
vocalizing whales within recording range could be identified
simultaneously with a minimum of effort and without
disturbing the animals. It offers a lot of pluses.”
for the pilot study were gathered during two trips to Norway
in 1997 and 1998. Dougherty worked off the country's
northern coast on a whale-watching boat, where the operators
made room for him and his equipment during tours. When the
boat got close enough to a whale, he would photograph it then
record the sounds it made as it dived. That way, he had a
record of which whales made what sounds.
ran the whale clicks through a computer program that uses an
algorithm he developed to analyze features of the sounds in
terms of ‘wavelet coefficients.’ Simply put, the program
looks at various ways the sound changes during the duration
of a click.
“For each whale, we had 100 clicks,” he said.
“We used random sets of 50 clicks for training and testing
the program. That allowed us to take many testing and
training sets from the data to build up statistics on the
With just one click, the computer was able to
correctly match a whale about 89 percent of the time.
Accuracy quickly improved when multiple clicks were used in
With five clicks, the computer scored 98.4
percent for correct matches. That climbed to 99.6 percent
for 10 clicks and 99.9 percent for 20 clicks.
“If we listen
to enough of a whale's signal, it becomes virtually
flawless,” he said.
Dougherty also refined a side benefit
to the process. He can acoustically measure the size of a
The big, blocky head that is the sperm whale's
trademark feature contains a large cavity filled with about
500 gallons of oil. When a click is produced, the sound
echoes within that chamber. Researchers can measure the echo
time and they know the speed at which sound travels through
the oil. That allows them to figure out how large the cavity
is. From there, it's a simple matter to calculate the size
of the whale.
“It's not the main thrust of the research,
but it's a pretty sexy side aspect,” he said.
plans to return to Norway soon to gather more data. He wants
to test his process on a larger group of animals and some
questions still need to be answered, such as how the whales'
signals change during the duration of their dives. He's also
constructing and testing acoustic buoys, which could listen
for sperm whales and send data to land-based labs, making
monitoring easier and less costly.
“We now know it's
feasible and it's promising,” Dougherty said. “But we need
to find out how robust it is.”
Dougherty, M. 1999
“Acoustic identification of individual sperm whales (Physeter macrocephalus)”MS Electrical Engineering Thesis, University of Washington.