[MARMAM] recent articles - dolphins and sonar; dolphins and noise

T. Aran Mooney amooney at whoi.edu
Fri Apr 10 08:27:46 PDT 2009

Could you please post the following articles regarding the effects of noise and
sonar on marine mammals.

Dear Colleagues,

The following articles were recently published online.

Sonar-induced temporary hearing loss in dolphins
T. Aran Mooney, Paul E. Nachtigall and Stephanie Vlachos
Biology Letters  published online 8 April 2009
doi: 10.1098/rsbl.2009.0099

There is increasing concern that human-produced ocean noise is adversely
affecting marine mammals, as several recent cetacean mass strandings may have
been caused by animals’ interactions with naval “mid-frequency” sonar.
However, it has yet to be empirically demonstrated how sonar could induce these
strandings or cause physiological effects.   In controlled experimental studies,
we show that mid-frequency sonar can induce temporary hearing loss in a
bottlenose dolphin (Tursiops truncatus).  Mild behavioural alterations were
also associated with the exposures.  The auditory effects were only induced by
repeated exposures to intense sonar pings with total sound exposure levels of
214 dB re: 1 μPa2∙s.  Data support an increasing energy model to
predict temporary noise-induced hearing loss and indicate that odontocete noise
exposure effects bear trends similar to terrestrial mammals.  Thus, sonar can
induce physiological and behavioural effects in at least one species of
odontocete; however, exposures must be of prolonged, high sound exposures
levels to generate these effects.

Predicting temporary threshold shifts in a bottlenose dolphin (Tursiops
truncatus): the effects of noise level and duration
T. Aran Mooney, Paul E. Nachtigall, Marlee Breese, Stephanie Vlachos and Whitlow
W. L. Au
J. Acoustical Society of America 125 (3), March 2009
DOI: 10.1121/1.3068456

Noise levels in the ocean are increasing and are expected to affect marine
mammals.  To examine the auditory effects of noise on odontocetes, a bottlenose
dolphin (Tursiops truncatus) was exposed to octave-band noise (4-8 kHz) of
varying durations (<2-30 min) and sound pressure (130-178 dB re: 1 μPa).
Temporary threshold shift (TTS) occurrence was quantified in an effort to: (i)
determine the sound exposure levels (SELs; dB re: 1 μPa2∙s) that
induce TTS and (ii) develop a model to predict TTS onset.  Hearing thresholds
were measured using auditory evoked potentials.  If SEL was kept constant,
significant shifts were induced by longer duration exposures but not for
shorter exposures.  Higher SELs were required to induce shifts in shorter
duration exposures.  The results did not support an equal-energy model to
predict TTS onset.  Rather, a logarithmic algorithm which increased in sound
energy as exposure duration decreased was a better predictor of TTS.  Recovery
to baseline hearing thresholds was also logarithmic (approximately -1.8
dB/doubling of time) but indicated variability including faster recovery rates
after greater shifts and longer recoveries necessary after longer duration
exposures.  The data reflected the complexity of TTS in mammals that should be
taken into account when predicting odontocete TTS.

A PDF copy of the Biology Letters article is available at:

Additional PDFs or further information is also available by emailing:
amooney at whoi.edu

T. Aran Mooney
Postdoctoral Scholar
Woods Hole Oceanographic Institution
(508)289-3714 (w)
(518)339-1151 (c)

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