Effectiveness of Acoustic Signals in Attracting Epipelagic Sharks to an Underwater Sound Source
Abstract:Three experimental studies were carried out in the field to determine the effectiveness of various acoustic signals in attracting free-ranging silky sharks, Carcharhinus falciformis, into the immediate vicinity of an under-water sound source. These studies were carried out over deep water in the Straits of Florida, miles from the mainland, as well as at a moored buoy in the Tongue of the Ocean, Bahamas.
All of the octave bands of noise used in the tests resulted in attraction, with the level of attraction increasing as the frequency spectrum decreased, respectively, from 500-1000 Hz, to 250-500 Hz, to 75-150 Hz, and finally, to 25-50 Hz. Irregularly pulsed signals were also more attractive than regularly pulsed signals, with the latter increasing in attractiveness as the pulse rate increased from 1, to 5, to 10, and finally to 20 pulses/sec. Additionally, it was established that, at least under certain conditions, sharks can be drawn away from one vessel by transmitting irregularly pulsed, low-frequency signals from another vessel, stationed a few hundred meters distant.
Various behavioral actions of individual sharks, after approaching a sound source, are described. Also various practical considerations, arising from the findings, are discussed.
Document Type: Research Article
Publication date: December 1, 1972
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