ODONTOCETE BIOACOUSTICS

All odontocetes that have been tested produce and hear broadband, high frequency sounds. Sound acquisition of marine mammals has been historically limited by equipment designed to record and play sounds within the human range of frequency sensitivity (e.g., sampling rate of 44.1 kHz). Recent advances in broadband acoustic acquisition have enabled researchers to examine the broadband content of odontocete phonations in the field.

Above: Dr. Marc Lammers (post doctoral fellow at MMRP) with the Underwater Dolphin Data Acquisition System (UDDAS). These systems are diver operated digital video/broadband acoustic recorders that have the ability to record simultaneous video and acoustic signals up to 200 kHz. This is a vast improvement over the traditional audio (< 20 kHz) limits of conventional recorders, considering that most dolphin species produce signals that are ultrasonic (i.e., above the human frequency hearing range). For more detailed information on the UDDAS visit: Oceanwide Science Institute

Above left: The The 4-channel UDDAS is a digital acoustic/video recording system that is battery powered and packaged in an underwater housing (developed by graduate student Michiel Shotten). Above right, the 4-channel UDDAS with diver. The four independent hydrophones allow sound source determination.

Above: Graduate student Michiel Shotten during post processing of acoustic data.

Figure 1 A spotted dolphin burst pulse representing both broadband (a) and narrowband (b) acoustic acquisition. The arrows represent peak frequency in each case. Notice the narrow band acquisition erroneously suggests peak frequency is around 2 kHz-3 kHz (from Lammers et al., 2003)..

 

Figure 2.A sequence of two spotted dolphins whistles (a) mixed with echolocation clicks (b) and burst pulses (c). The whistle contains 11 harmonics (numbered). From Lammers et al. (2003).

 

Figure 3. Spectrogram and power spectrum of a spinner dolphin whistle as it was recorded with a hydrophone of flat frequency response (a) and subsequently filtered with a frequency sensitivity curve approximating a stripped dolphin's audiogram (b) The solid vertical line represents where the 1024-point spectrum was measured. Represented on the spectrogram and the power spectrum are the fundamental frequencies (Fo) and harmonics (H1-3). Note that the fundamental is about 10 dB lower than the second and third harmonics in the filtered power spectrum.