An acoustically oriented article from the most recent issue (Volume
36, issue 3, 2010) of Aquatic Mammals:
Kvadsheim, P. H., Sevaldsen, E. M., Folkow, L. P., & Blix, A. S.
(2010). Behavioural and physiological responses of hooded seals
(Cystophora cristata) to 1 to 7 kHz sonar signals. Aquatic Mammals,
36(3), 239-247.
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Abstract
Controlled exposure experiments on captive hooded seals (Cystophora
cristata) were made to examine behavioural and physiological effects
of sonar signals. The animals were instrumented with data loggers
recording heart rate, dive depth, and swimming activity, and then
released into a 1,200 m3 net-cage in the ocean. The exposure consisted
of three different 1-s sonar signals covering the 1 to 7 kHz band
transmitted either by using 10-s inter-ping intervals and gradually
increasing source level from 134 to 194 dBRMS (re 1 ?Pa @1 m) within 6
min, or using the maximum source level of 194 dBRMS from the first
ping but gradually decreasing the inter-ping intervals from 100 s to
10 s within 10 min (duty cycle increasing from 1 to 10%). Transmission
loss from the source to the animal varied from 10 to 27 dB, depending
on the exact location within the net-cage and the transmitted
frequency. The animals responded to the initial (10% duty cycle)
exposure with avoidance to signals above 160 to 170 dBRMS (re 1 ?Pa)
received levels. This involved reduced diving activity, commencement
of rapid exploratory swimming at surface, and eventually displacement
to areas of least sound pressure level. However, already upon the
second exposure, the initial rapid swimming activity was absent, while
the reduction in diving activity became even more pronounced. No
differences were found in behavioural response to different
transmitted frequencies. Increased heart rate at the surface indicates
emotional activation during sonar exposure, but lack of effect of
sonar exposure on heart rate during diving indicates that
physiological responses to diving remain intact.
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