Abstract:

Attacks of pinnipeds on fish pens cause considerable destruction to the fish farming industry. An acoustic deterrent device (ADD) operated at 10--16 kHz with a source level around 200 dB re: 1 (mu)Pa at 1 m is an effective way of predation deterrence. The present technique is to operate the ADD system on a continuous basis. This constant insonification could lead to predator habituation and could create serious man-made acoustic noise. In this paper, techniques for creating a device to trigger the existing ADD system are investigated. The trigger will turn on the ADD system only when the fish pens are threatened. Field tests were conducted by applying both passive hydrophone and active Doppler methods to detect the presence of marauding pinnipeds. During the test, acoustic devices were located inside the fish pen or outside the fish cage, and the observation objects were fish in the pen or predators in the open sea. Design concept for the trigger devices, related DSP technique and pattern recognition, along with data collected in the field will be presented and discussed. [The principal investigator, Dr. Huang, acknowledges the funding from USDA/NRAC (Project No. 5555506).]