Telemetry Monitoring of Bottlenose Dolphin Biosonar during Dolphin-Human Interaction

Speaker:	Steve Birch
Affiliation:	Monash University

S. Birch & I. Cosic
Monash University
Dept. Of Electrical & Computer Systems Engineering
Caulfield Campus
P.O. Box 197
Caulfield East 3145 VIC
Australia

In order to investigate the link between dolphin acoustic emissions and modifications in human brain wave activity [1,2], a method currently under construction for monitoring dolphin biosonar emissions to which humans may be exposed is presented. It consists of a floating hydrophone and waterproofed signal analysis telemetry unit to allow open water interaction monitoring, with a radio link to a datalogger / computer analysis system.

The sonobuoy design incorporates a hydrophone [3] connected to a small float, within which an 8 bit flash converter converts the biosonar signal to digital format and presents it to a microcontroller. Here the signal undergoes signal analysis by fast Fourier transform and the resultant frequency spectra data is transmitted via a 300 Mhz radio transmitter. The radio receiver can be located aboard a nearby boat or onshore. Frequency spectra data can either be recorded onto an audio tape data logger for later analysis or fed directly into a computer for on site display and analysis. The hydrophone has a rated frequency response of 10 Hz - 200 kHz, and this entire signal will be subjected to analysis, thus encompassing the audible and ultrasonic range of frequencies produced by dolphins.

Due to the small size of the sonobuoy unit, subjects may have the sonobuoy unit attached to them via a short length of rope, alternatively it may be left free floating in one location or towed behind an attendant boat. One of the major advantages of this unit will therefore be its flexibility of operation, thus allowing monitoring of dolphin biosonar signals without hindrance from cables, both in tank studies and in open water.

[1] Cole D.M. (1994), Aquathought Foundation Report, Aquathought Foundation, 20231 Susanna Ave, Torrance CA, USA.

[2] Birch S.B. (1995), unpublished data from open water EEG measurements.

[3] Sea Systems Corporation: Model 1000R hydrophone, Sea Systems Corp.,PO Box 1759, Friday Harbor, WA 98250, USA