An acoustic tag for recording, directional, pulsed ultrasounds aimed at free-swimming Bottlenose dolphins (Tursiops truncatus) by conspecifics

• We developed an acoustic tag, called MOSART (MObile Submersible Acoustic Recorder of Transients), for recording directional social pulses produced by a bottlenose dolphin (Tursiops truncatus). The tag was attached to the dorsal fin of two dolphins by means of suction cups. Two adult bottlenose dolphins at the Kolmårdens Djurpark, Sweden, were trained to carry the tag comfortably through a desensitising program. The tag included two envelope click-detectors, each with a narrow bandpass filter, centred at 120 and 70 kHz, respectively. The duration of the original pulses and their relative amplitude within the two filter frequency bands was retained. The amplitude differences between the two filter bands reflected changes in the source frequency spectrum and/or the position of the tag hydrophone in the incoming sound beam. The tag recorded "echolocation click trains," "slow and irregular pulses," and "pulse bursts" with varying amounts of energy in both frequency bands. The peak amplitude and duration of clicks in "echolocation click trains" and in "slow and irregular pulses" were logged correctly; however, the tag recorder had more difficulties in handling the complex pulses in the aggressive "pulse bursts," where the duration of the individual pulses could not be determined. Still, the amplitude and the pulse repetition rate could be measured. The possible impact of the tag was investigated by analysing the dolphin's behaviours (12 categories), sounds (3 categories), preferred location in the pool, and respiration intervals. Only four of the behaviours and one preferred location in the pool showed significant differences among pre-tag baselines, tag periods, and post-tag follow-ups, suggesting that the tag had only a minor impact on the dolphin. We describe and discuss the tag and its capacity to record different pulsed sounds.

Nyckelord

acoustic tag

bottlenose dolphin

Tursiops truncatus

click detector

suction cup tag

directional pulse

broadband pulse burst

ultrasound

aggressive sounds

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