Comparing the biosonar signals of free swimming dolphins with those of a stationary dolphin in a net pen

Abstract

The biosonar signals of two free-swimming Atlantic bottlenose dolphins performing a complex sonar search for a bottom target in San Diego Bay were compared with the biosonar signals of a dolphin performing a target discrimination task in a net pen. A bite-plate device that the dolphins carried supported a hydrophone that extended directly in front of the dolphin. A biosonar measuring tootbox (BMT) attached to the bite plate measured the outgoing biosonar signals while the dolphins conducted sonar searches. Both of the free-swimming dolphins used different biosonar search strategy in solving the problem and their biosonar signals reflect the difference in strategy. The dolphin stationed in a hoop in the pen while echolocating on a target 6 m away and reported if the indentation on a spherical target was directed toward it. The signals were parameterized by determining the peak-to-peak source levels, source energy flux density, peaked frequency, center frequency, rms bandwidth, rms duration, and the Q of the signals. Some of the characteristics of the r signals were similar for the free-swimming and stationary dolphins while some were significantly different suggesting biosonar signals used by free-swimming animals may be different than signals used by captive dolphins in restrictive environments.