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article in Aquatic Mammals

Subject: article in Aquatic Mammals
Date: Tue, 21 Sep 2010 07:25:49 -0700
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.

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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