THE UNDERWATER SOUND OF GANGES RIVER
DOLPHINS (PLATANISTA GANGETICA)
KAZUHIRO MIZUE,* MASAHARU NISHIWAKI**ANDAKIRA TAKEMURA*
ABSTRACT

Various types of underwater sound emitted by the Ganges river dolphin
were studied. Clicks were 87% of all, seems to be a method of echo-location.
Bursts were 5 %, far more frequently than that of sea dolphins, must be a meansof communication. Twitterings or chirps appeared on the sonargram in a
stratified zone, are a pattern of burst. The sounds like mewing of cat andcreaking boat, were both appeared in a stratified zone. Among those appeared
in a stratified zone, some were proved to be quick repetition of clicks, others
did not appear in a click pattern however play back speed was reduced.
INTRODUCTION

From the view points of various field, Ganges river dolphin (Platanista gangetica) was
studied by Japanese scientists in Pakistan from October 1969 through March 1970.
The basecamp of the expedition was set at Mymensingh, East Pakistan throughout
the period. During the period, 20 individuals were caught by the local fishermen.
Among them, 4 living individuals were transported to Tokyo by air on February
4. This is an analysis on the underwater sound emitted by them.
On the other fresh water dolphins, the Amazon river dolphin (Inia geoffrensis)
and the buffeo negro (Sotaliafluviatilis), reports were presented by Shevill (1962),
Caldwell and Evans (1962). According to the reports, the above two species ofdolphins did not emit whistles but only clicks. However, Shevill wrote about hissusticion that Sotalia might emit whistles on some occasions.
Among the four species known as the members of the family Platanistidae,
only the Ganges river dolphin is believed to be blind and has a distinct swellingwall on the maxillary bones. Examination with a flashlight on and off at 10 cm
distant from the dolphin's eyes, showed no sign of reaction. Of course anatomicaland histological studies on those dolphins have been carrying on until present day,but the results have not been completed yet. Because of this species of dolphinsare supposed to be blind, we consider that they must rely much more on the guidanceof the underwater sound than the other dolphins with clear eyesight do.
An address about the experiment was given by M. Nishiwaki at the Seventh Annual Conference
on Biological Sonar and Diving Mammals held at the Stanford Research Institute on October 23, 1970.
Although Proceedings of the conference will be published, this report have to claim the originality.
* Faculty of Fisheries, Nagasaki University, Nagasaki.
** Ocean Research Institute, University of Tokyo, Tokyo.

Sci. Rep. Whales Res. Inst.,
No. 23, 1971. 123-128.

MIZUE, NISHIWAKI AND TAKEMURA

124METHOD OF THE STUDY

An indoor freshwater pool was set at a quiet place in the pine tree forest near byKamogawa Beach, about 60 miles distant from Tokyo. The pool was 7 m long,
4 m wide and 2 m deep. Inside of the pool was covered with plastic. The pool
was heat and sound proofed by the method of stuffing artificial fiber wool between
the cement base and the plastic cover. ·water and air temperature was kept constantly about 23°C.
As the pool had been so prepared that four individuals of Platanista and those of
two lnia were kept in it. Sex and body length of those were:Platanista

No. 1
No. 2
No. 3
No. 4
No. 1
No. 2

""
Inia""

118 cm
121
127
126
210
203

female""male"femaleAfter the dolphins had grown accustomed to the pool, recording of the underwater sound was carried out.
~lnia~

Platanista~,;------~l.. (f:'-'~~~~~-=-~

lL-----~

Fig. 1.

Situation of the pool, the Ganges river dolphins were in.

Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

UNDE
R』YATERSOUNDSOFPLATAJVISTA

125

Fi
rst,t
heunderwaters
oundemittedby al thedolphinsint
hepoolwasI・e・
cordedtwicefortota
l15hours. Thent
hepoolwasd
iv
ide
dintotwo. Thistime,
oneofthetwowas4m long
,3m wideandnat
ur
aly2m deep. Then,twoGanges
126cm maleand 127cm female) were putintoit
. Thesoundriv
erdolphins(emittion by thoseGange
sriv
erdolphinswasrecordedfortot
al5hours. In t
henextplace, a Gangesriv
er dolphin wasp
lacedint
hec
liv
iclec
lrect
a
ngu
larpool(
127cmfemale)and t
hes
ounde
mit
t
io
nbyi
tal
onewasr
e
c
or
dedf
o
rtwohou1
Thes
itu
at
i
onwasasappeari
nF
i
g.1.
Ther
ec
ordingap
paratu
seswereshowni
nF
ig
s.2and3.
・6
501,theOkiE
lectr
oni
csIndustr
yCo，・ Ltd.made.
l. Hydrophone,StyleSt噌Fig.2. Rccordmgapparatus.

Fig.3. Sonargraphapparatus.
Sci.Re/J・WhalesRes.Inst.
,λ匂 23.1.
971.

MIZUE, NISHIWAKI AND TAKEMURA

126

2. Pre-amplifier, Style St-65, the Oki Electronics Industry Co., Ltd. made.
3. Tape Recorder, Style No. 3, Nagura Electric Co., Ltd. made.
4. Sonargraph, Style SG-04Al, Rion Co., Ltd. made.
Performance of those apparatuses is shown in Fig. 4.
10o~-~-/-7~--~~-=----=-=--~_....,,,.,=----=~~,-.-:::~-:r-c A~Iii

D-20~ -llO

l:~-~i ! ~+16' i ! ~+ilf i ! ~+il:i•

E2

FREQUENCY (Hz)Fig. 4.

Performance of the apparatus.

RESULT AND DISCUSSION

1. Clicks: The Ganges river dolphins emitted cricks frequently. It was easily
presumed that the sound was emitted and received as a sense of echo-location.
Repetition rate of this sound was varied each time as indicated in Figs. 1
and 2 of Plate I. It was five times per second for the most seldom and 100 times
for the most frequent. The frequent emittions seem to have been aiming at near byobjects and the seldom emittions seem to have been aiming at distant objects. Thisphenomenon is equal to the dolphins at sea.
It is characteristic of this species, clicks went up to a fairly high wave frequency,
which is never reached by the sea dolphins. With our apparatus, as high as 20KHz
wave frequency was recorded. However, it is presumed that higher frequency
than that can be emitted by this species of dolphins. Shown in Fig. 3 of Plate I.
2. Bursts: Although sea dolphins too emit the bursting sound out. It seems
there is no special meaning with it. While this species of dolphins emitted bursts
not only once but multiple times at a time as usual. Frequency of this sound emittion is next to that of clicks though far less than the latter.
By the Ganges river dolphin, this sound seems to be used as a means of communication as well as following mentioned "twittering" sound. Sonargram of thissound is shown in Fig. 4 of Plate I. Observing the Ganges river dolphins in wildor in the pool, they seemed not to have lived in school but were swimming solitary
to and for in the river or in the pool. Communication between one another seemed
to have been rather infrequently. Need of communication is far more among sea
dolphins than by the solitary individuals.
3. Twitters: This is a sound heard like twittering of birds to human ears;
it is quite different from burstings. But, generally, there is no difference between
the two if the patterns of them appeared in the sonargram were analized. Bursts
continued about 0.4 seconds, comparatively longer period of a time, while twittersSci. Rep. Whales Res. Inst.,
No. 23, 1911.

UNDERWATER SOUNDS OF PLATANISTA

127

continued only about 0.1 second. This sound also seemed to be a means of communication. Sonargram of this is shown in Fig. 5 of Plate I.
4. Whistles: This species of dolphins emitted few whistles which are said tobe pure tone. How seldom the Ganges river dolphins whistles! Among sea dolphins,
the false killer whale (Pseudorca crassidens) whistles very often and the bottle-noseddolphin ( Tursiops gilli) seems to do conversation by the help of this whistles. However, we can hardly admit that the Ganges river dolphins are able to converse bymeans of their whistles. This sound may be emitted spontaneously by the Ganges
river dolphin. Sonargram of this is shown in Fig. 6 of Plate I.
5. Stratiform sound: In the sonargram, it was found a group of sounds whichwere appeared in parallel laminations. As it is well known, many species of sea
dolphins emit this stratiform sound spontaneously at times of mating, menacing
others of taking food etc. The Ganges river dolphins sometimes emitted a soundlike mewing of a pussy and some other times a sound like a creaking boat. Thesonargram indicated these in the patterns of stratiform sound. ·watkins (1967)
considered this type of sound to be a very quick repetition of clicks.
Fig. 1 of Plate II shows this type of sound playback at the natural speed oftape-rotation. Fig. 2 of Plate II show5 the same sound at half rotation speed,that is, the wave frequency was reduced in half cycle. At this speed, the pattern
still shows parallel laminations. However, as in Fig. 3 of Plate II, when taperotation was reduced to 1/4 at speed, analysis of the sound did not appear in parallel
laminations. It appeared in the typical clicks pattern. The opinion of Watkins
was proved.
But on the other hand, the sound similar to mewing of pussy did not appear
in the clicks pattern, even when the speed was reduced to 1/4 (Fig. 5 of Plate II),or even to 1/12 as shown in Fig. 6 of Plate II. It did not appear in the clicks pattern.
The sound of this type is emitted by various species of dolphins very often and thesound of the killer whale (Orcinus orca) is almost always of this type. We came toconclude that this type of sound of parallel laminations must have been different
from what Watkins wrote about. It is yet unknown whether these sounds werespontaneously emitted or not.
In the following, above mentioned variety of sounds are shown in the rate offrequency.
Clicks . .
87%
Bursts . .
5%Twitters 3%
Whistles 1%
Stratiform sounds (parallel laminations)4%
Total . . . . . . . . . . . . . .
.100%
ACKNOWLEDGEMENT\\Te extend our sincere appreciation to the stuff of the Kamogawa Sea ·world forgiving us convenience to have kept and have studied the Ganges river dolphins.
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

MIZUE, NISHIWAKI AND TAKEMURA

128

Acknowledgement is made of the financial support of this investigation throughgrants from the Ministry of Education of Japan as a part of the Fund of Scientific
Investigation Abroad.
REFERENCESCALDWELL, M. C., D. K. CALDWELL and W. E. EVANS, 1962. Sound and behaviour of captive Amazon
freshwater dolphin, Inia geojfrensis. Cont. in Sci., 108: 1-24.
ScHEVILL, W. E. and W. A. WATKINS, 1962. Whale and porpoise voices. A phonograph record. 24 pp.
and a phonograph disk. Woods Hole, Mass.: Woods Hole Oceanographic Institution.
WATKINS, W. A., 1967. The harmonic interval fact or artifact in spectral analyses of pulse frain. Marine
Bioacoustics II: 15-43.

EXPLANATION OF PLATESUnderwater sound emitted by Ganges river dolphin.
PLATE I
Fig. I.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.

ClicksClicks.
Clicks.
Bursts.
Twitters.
Whistles.
PLATE II

Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.

Stratiform sound at natural speed of tape-rotation.
Stratiform sound in Fig. 1 reduced to half speed rotation.
Stratiform sound in Fig. 1 reduced to l /4 speed rotation.
Stratiform sound at natural speed of tape-rotation.
Stratiform sound in Fig. 4 reduced to 1/4 from natural rotation speed.
Stratiform sound in Fig. 4 reduced to lj12 from natural rotation speed.

Sci. Rep. Whales Res. Inst.,

No. 23, 1971.

"'。

官、

{'JO
6r'a・u・SJ！
u・／a＜I・‑A/lll/3uSas1・us1・'ω0・0

明川一

lFREO.<k zu司I I I目・・．
品.
.
.

0。

ー0.
:︸
・M
・zm品目mn−↓ON00.

aー
罰0l
b個0"'0"'︒
・1︒−ReFoE−︒︐︐ztuR l

J 0・− m~

CKHd
開 臼.

; ~・ ;， 円

信 一：

一̲J lO一̲j̲一

Ul0N

9.
.

zmA鍋 向 ︒ ︾﹃−Jn ・︸
4−玄 問︷帥同o h o由JVι;uー。
。

ιth・︐︑司︒︒．︐JEf︑︐︒r
川ー〜J T．
．

。

。

Ni

べJ ·~1 nz 1 1¥.
'河V MJHSl，Cl¥:V 1・」
VJ)
J:
ぺ:
v11m

J
J
LV't.
I:

I
PLA1E JDTAKEMURA
T
¥
:
AKTA
"
¥¥
UI
SI
¥
.:
ZUE
MI崎

7 yddいHA

0N，.·~~ ／由−僻仙総dj・岨Or

τ円bト日LL

AU凶的︸凶主−ト− o−∞．0

一戸・︷・同峨滞伊織紛争~：：·1.

マJ N

ド与供 引J,l.
・.

.
＇.
＂同j,
̲jl0ヨ
ZH刑・(0"'・時

4‑宮.
.
0。
例zω−wa

創刊
︒

−︒ −
凶P。

−
一mH
N・Fち
01「一一一「ー.
:w‑N

的"II'制10uc−（•“対》。ヨ凶4.
tsn.IssRee.Whal.Rψ
ic
S
9il.
.1
3.2oX