International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 6

Number 4

December 2012

1 INTRODUCTION

The Under Water Speaker (UWS) has been installed

on the hydrofoils (HF) for avoiding the collisions

with large cetaceans. However, its utility is still

uncertain whether the sound produced by the UWS

corresponds to the audible range of major large

cetaceans. This is a major reason why we conduct

the present study which explores the way to improve

the UWS from biological aspects. Under the present

research project, we examined three sub-projects:

1.1 Characteristics of the HF underwater noise

One of the reasons of the collision is considered that

the HF underwater noise is possibly hard for

cetaceans to recognize approaching vessel. It is

probably because the noise level is too low and

hardly transmits to a long distance. Therefore we

analyze the characteristics of the HF underwater

noise.

1.2 Assessing audibility by measuring of

vocalization

The UWS should be improved to prevent the

collision incorporating with the audible range of

causal cetaceans. Currently, there are no direct

measures of audible range for any large cetaceans

because they cannot be investigated with

conventional audiometric techniques of

psychoacoustical or electrophysiological analysis.

However, the audible range can be assessed by

vocalization, as to correspond the dominant

frequencies of the vocalization (e.g. calls) to the

most sensitive region of receptor system in

vertebrate taxa (Green and Marler 1979). Shakata et

al. (2008) identified sperm whale (Physeter

macrocephalus), Baird's beaked whale (Berardius

Estimation on Audibility of Large Cetaceans

for Improvement of the Under Water Speaker

H. Yamada, L. Kagami, Y. Yonehara, H. Matsunaga, & H. Kato

Tokyo University of Marine Science and Technology, Tokyo, Japan

M. Terada

KHI JPS Co., Ltd., Kobe, Japan

R. Takahashi

Kawasaki Heavy Industries Ltd., Kobe, Japan

K. Okanoya

RIKEN Brain Science Institute, Wako, Japan

T. Kawamoto

Tsurumi University, Yokohama, Japan

ABSTRACT: In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker

(UWS) has been installed on the HF.

Because of its potential in utility, we tried to improve the UWS to

minimize the risk of the collisions. Under our project, we examined three subprojects; 1) Analyzing the

characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring

their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal

membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise

with approximately 150dB re 1μPa-m.That noise level was lower than those of larger boats suggesting

difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and

anatomical obervation indicated that dominant frequency of their audible range was lower than signals

produced by the existing UWS.

589

bairdii), common minke whale (Balaenoptera

acutorostrata), Bryde's whale (Balaenoptera edeni)

as possible causal species of the collision on the sea

route of the HF in Japanese water. Among these

species, we chose to sample the vocalization of

sperm whale and Bryde’s whale since relatively

easier to record their vocalizations in Japanese

water. Based on the recorded vocalization, we

assessed the audible range of these species.

1.3 Anatomical Predictions of the Audible range

Alternatively, a comparative anatomy approach is

the useful way to estimate the audible range because

anatomical structure of inner ear correlates to

frequency range in multiple mammalian species

(Echteler et al., 1994). In particular, the cochlear

configuration and thickness to width (T/W) ratios of

the basilar membrane in inner ear are consistent with

the maximal and minimum frequencies for each

cetacean species (Ketten and Wartzok, 1990). This

study estimates the audible range of common minke

whales and Baird's beaked whale by describing the

anatomy of their inner ears and applying the model

described by Ketten (2000).

2 METHODS

2.1 Characteristics of the HF underwater noise

Underwater noise of the HF, SUISEI: 169gt.

LOA31.2m (Owned by Sado Kisen Co.,Ltd.), was

recorded during its cruise at service speed (38-39kn)

from a small vessel at a distance of 100m.

Recordings were made using a OKI SEATEC

model OST2130 (frequency response 10Hz to

100kHz) omnidirectional hydrophone has sensitivity

of approximately -174±3dB re 1V/μPa with 10m

cable. It was connected via pre-amplifiers

(frequency response from 20Hz to 20kHz), on a

Sony PCM-D50 digital recorder (16bit 44.1 kHz)

and OKI SEATEC OST4100 Hydroacoustic

analyzer which was used to analyze the sound

source level. This recording chain had a flat

frequency response from 20Hz to 20 kHz. The HF

underwater noise was assessed by 1/3-octave bands

analysis using Avisoft SASLab Pro (Avisoft

Bioacoustics, Germany.Ver.4.1.) because noise

levels in 1/3-octave bands are useful in interpreting

noise effects on animals. The estimated source levels

of underwater noise (at 1m) of the HF were

calibrated by Transmission Loss and Absorption

Loss (Francois & Garrison1982).

2.2 Assessing audibility by measuring of

vocalization

Bryde’s whale sounds were recorded in the waters of

Kochi on the south western coast of Japan (32º40' to

33º2'N, 133º00' to 133º13'E) for five days in mid-

October, 2008. The study area ranged from the south

coasts out to approximately 30km (16 nmi) of the

shore. We chartered a fishing-boat for recording.

When cetaceans were sighted, the boat approached

to confirm species and school size and to collect

other relevant information. When sighting Bryde’s

whale, the hydrophone was thrown in water and

started recording. Signals were recorded with a OKI

SEATEC model OST2130 omnidirectional

hydrophone with 15m cable, connected via pre-

amplifiers (frequency response 20Hz to 20kHz), on

a Sony PCM-D50 digital recorder(16bit 44.1 kHz).

This recording chain had a flat frequency response

from 20Hz to 20 kHz. The acoustic characteristics of

phrases were examined by using the analysis

software Avisoft SASLab Pro, with spectrogram

parameters of 512-point FFT size, 75.0% overlap,

and Hamming window. The vocalization was

analyzed based on the following parameters;

duration, peak frequency, and fundamental

frequency of element.

Sperm whale sounds were recorded off the

southeastern coast of Chichijima, the Bonin

(Ogasawara) Islands (26º55' to 27 º05 'N, 142º11' to

142º24'E) for eight days in September, 2009. We

chartered a fishing-boat for recording. When sperm

whales were sighted the boat approached to confirm

school size and to collect other relevant information.

When sighting sperm whale, the hydrophone was

thrown in water and their vocalization was recorded.

Signals were recorded with recording system

described above in Bryde’s whale sounds recording.

2.3 Anatomical Predictions of the audible range

Ear bones of 9 specimens of common minke whales

(9 individuals) and 6 of Baird's beaked whales (3

individuals) were collected (under cooperation with

The Institute of Cetacean Research, Tokyo Japan

and National Research Institute of FarSeas Fisheries,

Yokohama Japan) and analyzed. Ears were frozen

shortly after the collection and placed in a buffered

10% formalin solution. All ears were scanned by the

nuclear magnetic resonator (NMR) (Bruker Bio Spin

AVANCE 400WB) to measure the cochlear

configuration. The ears were decalciﬁed in 5%

formic acid for three weeks and processed into slides

10-μm cryosections by the Kawamoto film-

sectioning method (Cryofilm transfer kit; Leica

Microsystems) (Kawamoto 2003). Every 10

section

was stained with hematoxylin and eosin and

mounted. Basilar membranes were shown by a laser

scanning microscope Olympus Model FV1000 at a

590

×10 (width) × 20 (thickness) objective

magnifications with a scale and ocular calibrated

scale for measurements. The basilar membranes

were measured for width and thickness using ImageJ

(National Institutes of Health, USA. Ver.1.43.).

3 RESULTS

3.1 Characteristics of the HF underwater noise

Underwater noise of the HF was a “broadband”

sound with energy spread continuously over a range

of frequencies.

10 100

1000 10000

120

130

140

150

160

170

180

190

200

5m Zodiac

Trawler

34m Diesel

7.3m Outdr

Tug/Barge

Icebreaker

Supertanker

Frequency (Hz)

1/3-OB Level (dB re 1

Pa-m)

Figure 1. Estimated 1/3-octave source levels of underwater

noise (at 1m) of the HF and other vessels summaries of

Richardson et al.(1995).

Source levels at 1m were estimated by cylindrical

spreading transmission loss TLc = 10log r (dB) and

absorption loss (Francois & Garrison1982) with

distance from source (100m), water depth (88.8m),

water temperature (19°C), salinity (35‰), pH (8).

As a result, the estimated source level was 146.3±2.6

dB re 1μPa-m(Mean±SD) with peak sound level of

151.4 dB re 1μPa-m at 6,300Hz. The sound level of

the HF was almost equal to that of small ships

(Fig.1).

3.2 Assessing audibility by measuring of

vocalization

48 biological sounds estimated to be emitted by

Bryde’s whale were recorded during a total of

8h24m15s recording time. We judged whether

sounds were emitted by Bryde’s whale based on the

following two points, 1) any marine animals other

than Bryde's whale were not visually-observed

during recordings, 2) these sounds showed

similarities to Bryde’s whale vocalizations described

by Oleson et al. (2003). These sounds were assigned

to two categories: a) swept tonal call, b) harmonics

call (Fig.2).

1 Swept tonal call [Fig.2(a)] was detected 46/48

calls. Table 1 indicates a summary of the quanti-

tative parameters of this call type. These calls

were tonal and frequency modulated sounds char-

acterized by an arch-like structure and no repeti-

tion. The mean peak frequency of these calls was

269.9Hz±71.3 (mean±SD) ranging from 131.6Hz

to 373.4Hz. The mean duration for this call type

was 0.71 s±0.30 (mean±SD). This type calls were

first recorded off the coast of Japan.

Figure 2. Envelope curves and spectrograms of two phrase

types attributed to Bryde’s whales in Japan. (a) Swept tonal

call (b) Harmonics call. Both spectrograms were made with a

512-point FFT, 75.0% overlap, and Hamming window.

2 Harmonics call [Fig.2 (b)] was detected only 2/48

calls in this study. The calls included higher-

frequency harmonics [fundamental frequency

78.5(74.0-83.0) Hz] than these reported by Ole-

son et al. (2003) (approximately 45Hz). The

mean of duration for this call type was 0.28 (0.17-

0.39) s.

A total of 12547 clicks of sperm whales were

recorded during a total of 7h20m23s recording time

(Fig.3). Table 1 indicates a summary of the

quantitative parameters of clicks. The peak

frequency of the clicks was 3174Hz (geometric

mean, 95% Cl 3140-3208). The duration of the

individual pulses within a click is

9.27±0.05ms(Mean±SD). The recorded levels of the

clicks were approximately 150 dB re 1μPa.

Figure 3. Envelope curves and spectrograms of the clicks of

sperm whales. Spectrograms were made with a 512-point FFT,

75.0% overlap, and Hamming window.

591

Table1. Frequency quantitative parameters for vocalization.

__________________________________________________

Species Sound Frequency Peak

(Whale) type Range(Hz) Frequency(Hz)

__________________________________________________

Bryde’s Swept tonal call 131.6-373.4 269.9±71.3

whales (n=46) (Mean±SD)

Harmonics call 250.0-293.0 271.5

(n=2) (Mean)

Sperm Clicks 1870-4780 3174

Whales (n=12581) (3140-3208)

(GM, 95% Cl)

__________________________________________________

3.3 Anatomical Predictions of the audible range

Initial surveys of cochlear dimensions from NMR

images showed that common mike whales cochlear

were type M while Baird's beaked whales cochlear

were type II (Ketten 2000) (Fig.4a). Furthermore we

measured the cochlea length and other cochlea

configurations shown in Table 2. It took

approximately 3 weeks to complete decalcification

of the cochlear. The Kawamoto film-sectioning

method allowed the best preparation of thin sections

from specimens of the cochlear (Fig 4b). All

specimens had measurable intact basilar membranes

in apex and base region of the cochlea(Fig 4c).

Table 2 shows the thickness/width ratios and

estimated frequency of the audible range for each

species from the data using the model described in

Ketten (2000).

Figure 4. Images of cochlea from Baird's beaked whales. a) A

three-dimensional reconstruction by NMR. b) Images from

histology slide preparations. c) The basilar membrane(arrow)

of the cochlea basal turn (20×)

Table 2. The cochlear spiral and the basilar membrane

measurements, and predicted frequency of the audible range

from the measurements [the model described in Ketten (2000)].

__________________________________________________

Species Common minke Baird's beaked

whales (n=9, whales (n=6,

9individuals) 3individuals)

__________________________________________________

Number of turns 2.32(±0.09) 2.08(±0.09)

Membrane Length(mm) 54.82(±2.20) 54.44(±2.35)

Basal diameter (mm) 12.36(±0.83) 16.14(±2.35)

Axial height (mm) 7.36(±0.55) 7.66(±1.09)

Membrane Thickness

Base/Apex (μm) 9.0/5.4 15.9/13.5

Membrane Width

Base/Apex (μm) 171.4/1128.0 142.4/304.5

T/W ratio

Base/Apex 0.0525/0.0098 0.1568/0.020

__________________________________________________

Predicted Frequency (kHz) 15.93/0.12 33.09/0.27

__________________________________________________

4 DISCCUSION

Large cetaceans response to sound level higher than

from 110 to 170dB re 1μPa (Richardson et al 1995),

and it requires 170dB re 1μPa to trigger a strong

reaction when they are away from the source

(Akamatsu 1993). Since the HF cruising sound level

at 100m from source had 126.3dB re 1μPa (source

level 146.3 (±2.6) dB re 1μPa-m) was probably too

low to make whales react to the sound. In addition,

peak frequency of the HF may be higher (6.3 kHz)

than sensitive hearing of large cetaceans. Therefore,

it is necessary to install the UWS that effectively

produces sounds that make whales recognize the

approaching the HF.

Because it is to correspond the dominant

frequencies of the vocalization to the most sensitive

region of receptor system in vertebrate taxa (Green

and Marler 1979), the present study assessed the

dominant audible ranges for each whale as follows;

Bryde’s whales 0.1-0.4kHz, sperm whales1.9-

4.8kHz.

Alternatively, an anatomical structure of inner ear

correlates to the maximal and minimum frequency

of the audible range in each cetacean species (Ketten

and Wartzok, 1990). Therefore the audible ranges for

each whale were predicted as follows; common

minke wahles: 0.1-15.9kHz and Baird's beaked

whales:0.06-33.1kHz.

Thus, it is considered that the existing the UWS

(6-20kHz) is necessary to be modified to produce

the lower frequency down to less than 15.9kHz for

common minke whales, to less than 0.4kHz Bryde’s

whales, and between 1.9 to 4.8kHz for sperm whale.

As for Baird's beaked whales, predicted audible

rangea are well inside of those by the existing UWS.

However the vocal frequency for Bryde’s whales is

fur below of to lower band by the UWS. The gaps

are thought to be technically difficult to fill up.

Because the frequency of vocalization is certainly

within the audible range and the practical audible

range is much wider, this must be investigated by

further examination through anatomical approach

mention above.

For further study, it is necessary to improve the

acoustic property of the UWS based on the sound

known to have a repellent effect against large

cetaceans within the frequency range shown in this

study.

5 CONCLUSION

The HF noise level was probably too low to make

whales react. Therefore, it is necessary to install the

UWS effectively. Based on vocalizations and

anatomical observation, it is considered that the

592

existing the UWS (6-20kHz) is necessary to be

modified to produce the lower frequency down to

less than 15.9kHz for common minke whales, to less

than 0.4kHz Bryde’s whales, and between 1.9 to

4.8kHz for sperm whale.

ACKNOWLEDGMENT

We would like to special thank for supporting for

investigation Sado Kisen Co., Ltd. Ougata-cyou

Yugyo-sensyukai (Whale watching association),

Ogasawara whale watching association and

Ogasawara Marine Center. Special thanks to Ms. M.

Yamaguchi and Mr. A. Nakajima, who helped us

recording of sperm whales. Key specimens provided

by the Institute of Cetacean Research and National

Research Institute of FarSeas Fisheries. Thanks to

Laboratory of Maine Biology, Tokyo University of

Marine Science and Technology and

Biolinguistics,RIKEN Brain Science Institute. This

work supported by Kawasaki Heavy Industries

Co.,Ltd and KHI JPS Co., Ltd.,.

REFERANCES

Akamatsu, T., Hatakeyama, Y. & Takatsu, N. 1993. Effects of

pulse sounds on escape behavior of false killer whales.

Nippon Suisan Gakkaishi. 59(8):1297-1303.

Echteler, S.W., Fay, R.R & Popper, A.N. 1994. Structure of the

mammalian cochlea. In: A.N. Popper.(eds), Comparative

hearing: mammals :134-171.New York. Springer-Verlag.

Press.

Francois, R.E. & Garrison, G. R. 1982. Sound absorption based

on ocean measurements: Part I: Pure water and magnesium

sulfate contributions. Journal of the Acoustical Society of

America. 72(3): 896-907.

Green, S & Marler, P. 1979. The analysis of animal

communication. In: P. Marler & J.G. Vandenbergh. (eds),

Social behavior and communication, vol 3. Handbook of

behavioral neurobiology: 73-158. New York. Plenum

Press.

Kawamoto, T. 2003. Use of new adhesive film for the

preparation of multi-purpose fresh-frozen sections from

hard tissues, whole-animals, insects and plants. Arch.

Histol. Cytol .66(2):123-143.

Ketten, D.R & Wartzok, D. 1990. Three-dimensional

reconstructions of the dolphin ear. In: R. Kastelein.(eds),

Sensory abilities of cetaceans. :81-105.New York: Plenum

Press.

Ketten, D.R. 2000. Cetacean ears. In: R.R. Fay. (eds), Hearing

by whales and dolphins: 43–108.New York. Springer-

Verlag Press.

Oleson, E.M., Barlow, J., Gordon, J., Rankin, S., &

Hildebrand, J. A. 2003. Low frequency calls of Bryde’s

whales. Marine Mammal Sci. 19: 160–172.

Richardson, W.J. 1995. Marine mammal hearing. In:W.

Richardson,C.R.Greene, C.I.Malme & D.H.

Thomson.(eds), Marine Mammals and Noise.:205-240.

California. Academic press.

Shakata, K., Odagawa, A., Yamada, H., Matsunaga, H., &

Kato, H. 2008. Toward to avoiding ship strike of cetaceans

with the high-speed HF(1)-Identifying expected cetacean

species on the track lines of HF. 2008 Annual meeting of

M.S.J. summary :135

593