TTS & behavioral response studies with harbor porpoises related to naval sonar:Use of results for regulation & mitigation

Ron Kastelein & many team members

SEAMARCO

3S symposium

October 28, 2015

St. Andrews, Scotland

Why focus

on

harbor porpoises ?

A) Sensitive hearing, wide frequency hearing range

B) Low behavioral response threshold SPLs

C) Large distribution area in Northern Hemisphere

Structure of talk

TTS studies & BRS research

• Why?

• Studies conducted with harbor porpoises

• Importance of results for regulation & mitigation

• Planned research with harbor porpoises

4

Why TTS research ? (Driving force)

TTS onset SELs and growth rates are used to estimate PTS onset SELs which are used as underwater sound criteria by regulators to prevent hearing injury

TTS sub-studies

• Determine affected hearing frequencies

• TTS growth related to SPL, duration, duty cycle

• Determine time for hearing to recover

TTS measurement session

1) Pre-exposure hearing test

2) Fatiguing noise exposure

3) Post-exposure hearing tests

Control sessions

Control sessions are conducted without the fatiguing noise to get insight in the fluctuations of the hearing thresholds, due to time of day and methodology.

Effort

1 session per day to prevent hearing damage

(data collection is labor-intensive & slow)

HF

125 64 32 16 8 4 2 1 0.5 (kHz)

Filter bands in cochlea

Hearing frequency most affected (i.e., highest TTS)

TTS studies with LFAS (1-2 kHz) & MFAS (6-7 kHz)(Netherlands Ministry of Defense)

Highest TTS at frequency of fatiguing noise (1.5 kHz)

Porpoise echoloc. frequency (~125 kHz) not affected

Affected hearing frequencies

Affected hearing frequencies

Fatiguing noise: 6.5 kHz CW

Most affected frequency depends on received SPL

Region of critical level for 100% duty cycle

TTS growth due to increase of SPL

Fatiguing noise: 1-2 kHz down-sweeps

Increase in TTS growth rate indicates approach PTS onset SPL

Recovery of hearing

After 1-2 kHz sweeps, 100% duty cycle

Above critical level, much longer recovery

Getting near the danger zone (near PTS)

Indication how recovery time from TTS indicates approach to PTS onset SPL

16 hr

Est. of PTS onset SELcum based on TTS growth curves(Fatiguing noise: 6-7 kHz sweeps)

100% D.C.

10% D.C.

40 dB TTS = PTS

PTS onset SELcum: 196 206

Equal energy model (prediction of TTS)Duration - SPL

Exposure expressed as SELcum

Inter-pulse intervals play a major role in TTS induced• Hearing may partly recover during inter-pulse intervals• It determines the sound energy per time unit (Leq)

-3

0

3

6

9

12

15

18

21

24

27

30

33

172 175 178 181 184 187 190 193 196 199 202 205 208

TT

S1

-4 (d

B)

Cumulative sound exposure level (dB re 1 µPa2s)

SPL variation, 100% Duty Cycle

SPL variation, 10% Duty Cycle

Duration variation, 100% Duty Cycle

Duration variation, 10% Duty Cycle

0

2

4

6

8

10

12

14

170 180 190 200 210

TT

S1

-4(d

B)

SELcum (dB re 1 µPa2s)

Harbor porpoise hearing is more prone to TTS

after exposure to 6-7 kHz than to 1-2 kHz sweeps

6-7 kHz sweeps

1-2 kHz sweeps

Effect exp. freq. on TTS onset SELcum & growth rate

Comparison LFAS and MFAS results (10% D.C.)

Importance results TTS studies for regulation

Future underwater sound criteria to prevent PTS should:

• Specify not only SELcum , but also duty cycle.

• Specify the frequency (spectrum) of the sounds.

• Take into account affected hearing frequencies.

• Specify ecological most relevant frequency

hearing ranges of marine mammal species.

Importance results sonar TTS studies for mitigation

(for porpoises, possibly all odontocetes)

• Reduce the duty cycle

• Lower the frequency

• Reduce the level of harmonics

0

2

4

6

8

10

12

14

170 180 190 200 210

TT

S1

-4(d

B)

SELcum (dB re 1 µPa2s)

6-7 kHz sweeps

1-2 kHz sweeps

53-C sonar ?(3 kHz)

Planned TTS research with harbor porpoises

TTS growth due to 53-C sonar of the US navy

(3 kHz) (LMR program)

TTS in harbor porpoises

due to impulsive sounds such

as those produced during

seismic surveys and explosions

JIP program of IOGP (TNO, SEAMARCO)

30

50

70

90

110

130

150

170

190

210

230

0.1 1 10 100 1000

SE

L (

dB

re

1µ

Pa

2s

)

Frequency (kHz)

Hearing threshold (Kastelein et al., 2010)

Kastelein et al. (2012)

Kastelein et al. (2013)

Kastelein et al. (2014a)

Kastelein et al. (2014b)

~8 dB TTS

LFAS

1.5 kHz CW

1-2 kHz sweep

Research needed: Equal-TTS contours harbor porpoises

(Example: SELcum causing 8 dB TTS; all 1 hr exposures,100% DC)

Noise bandat 4 kHz

MFAS

6.5 kHz CW

6-7 kHz sweep

110 d

B

115 d

B

110 d

B

? (<1 kHz)

? (7-150 kHz)

Why behavioral response studies (BRS) ?

Usually only a small number of animals is close enough near a high energy sound source to get a PTS.

However, a much larger number of animals respond behaviorally to high energy sound sources, as the behavioral threshold SPL is often lower than the SPL in PTS onset SEL.

Behavioral response studies (BRS) in pool with porpoises (Netherlands Ministry of Defense)

•Received levels of single sonar sweeps causing a startle response in 50% of pres. (LFAS: 1-2 kHz and MFAS: 6-7 kHz).

•Received levels of series of sweeps causing behavioral responses (LFAS: 1-2 kHz and MFAS: 6-7 kHz) (19% duty c.).

•Effect simulated Sea State noise on effect of series of 6-7 kHz up-sweeps (MFAS) on behavior.

•Received levels of series of 4 HELRAS signals causing behavioral responses (8% duty cycle).

22

Startle response threshold level (single emission)

1-2 kHz without harmonics needs to be loud to cause effect

Concl.: LFAS can be louder than MFAS, avoid harmonics

1-2 kHz

Up & down-sweeps

1-2 kHz

Up & down-sweeps

& harmonics

6-7 kHz

Up & down-sweeps

Specify parameters of d.c.:

signal duration & interval

BRS for Swedish Ministry of

Defense (25 kHz)

The lower series has more

effect on behavior

50% duty cycle

Importance of BRS results for regulation

Underwater sound criteria to reduce behavioral

responses should:

• Not only specify SPL, but also direction of sweep

• Specify the frequency (spectrum) of the noise

(or weight the level).

• Differentiate between continuous sounds &

intermittent sounds.

• If intermittent, specify the duty cycle. More

importantly, specify inter-pulse interval.

Importance of sonar BRS results for mitigation

(for harbor porpoises, possibly other odontocetes)

• Use continuous sounds instead of intermittent

• If intermittent, increase the inter-pulse interval

• Use noise instead of tones or sweeps

• Lower the frequency

• Produce down-sweeps instead of up-sweeps

Planned sonar BRS with harbor porpoises

BRS with 53-C sonar sounds of US navy at various

duty cycles and under various background noise

levels (LMR program)

27

Funding agencies:

Netherlands Ministry of Defense

(René Dekeling)

Swedish Defence Research

Agency (FOI)

(Torbjörn Johanson &

Mathias Andersson)

LMR program, US Navy

(Anu Kumar)

Thank you for your attention !

SEAMARCO

Research for marine conservation

researchteam@zonnet.nl