Some Observations on the Prey Stunning Hypothesis

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259

Toothed whales (Cetacea, odontoceti) emit sound pulses to probe their surroundings by active echolocation. Noninvasive, acoustic Dtags were placed on deep-diving Blainville's beaked whales (Mesoplodon densirostris) to record their ultrasonic clicks and the returning echoes from prey items, providing a unique view on how a whale operates its biosonar during foraging in the wild. The process of echolocation during prey capture in this species can be divided into search, approach and terminal phases, as in echolocating bats. The approach phase, defined by the onset of detectable echoes recorded on the tag for click sequences terminated by a buzz, has interclick intervals (ICI) of 300-400·ms. These ICIs are more than a magnitude longer than the decreasing two-way travel time to the targets, showing that ICIs are not given by the two-way-travel times plus a fixed, short lag time. During the approach phase, the received echo energy increases by 10.4(±2)·dB when the target range is halved, demonstrating that the whales do not employ rangecompensating gain control of the transmitter, as has been implicated for some bats and dolphins. The terminal/buzz phase with ICIs of around 10·ms is initiated when one or more targets are within approximately a body length of the whale (2-5·m), so that strong echo returns in the approach phase are traded for rapid updates in the terminal phase. It is suggested that stable ICIs in the search and approach phases facilitate auditory scene analysis in a complex multi-target environment, and that a concomitant low click rate allows the whales to maintain high sound pressure outputs for prey detection and discrimination with a pneumatically driven, bi-modal sound generator.

Section: Discussionmentioning

confidence: 99%

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Madsen

Johnson

Soto

et al. 2005

270

259

“…(Zagaeski, 1987;Mackay and Pegg, 1988). However, long duration sounds had a debilitating and, in some cases, lethal effect on guppies, Lebistes reticulatus (Zagaeski, 1987). Underwater tail slaps produce several transient sounds of a long total duration, which potentially could have a debilitating effect on the fish.…”

mentioning

confidence: 99%

“…We suggest that multiple factors generated by the tail slaps like particle fluctuations, turbulence, pressure changes and physical impact cause debilitation of herring. (Zagaeski, 1987;Mackay and Pegg, 1988). However, long duration sounds had a debilitating and, in some cases, lethal effect on guppies, Lebistes reticulatus (Zagaeski, 1987).…”

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confidence: 99%

Acoustic characteristics of underwater tail slaps used by Norwegian and Icelandic killer whales (Orcinus orca) to debilitate herring(Clupea harengus)

Simon

Wahlberg

Ugarte³

et al. 2005

SUMMARY Norwegian killer whales debilitate prey by slapping their tails into herring schools. These underwater tail slaps produce a thud-like sound. It is unclear whether this sound is caused by cavitation and/or physical contact between herring and whale tail. Also the forces causing debilitation of the fish are not understood. Here we present an acoustic analysis of underwater tail slaps using a multi-channel wide (150 kHz) band recording system. Underwater tail slaps produced by Norwegian killer whales generated sounds consisting of multiple pulses with source levels of 186±5.4 dB (pp)re.1 μPa at 1 m (±1 s.d., N=4). The –3 dB and 97% energy bandwidths were 36.8±22.5 kHz and 130.5±17.5 kHz(±1 s.d., N=13), respectively, with a centre frequency of 46.1±22.3 kHz. The similarities between the acoustic properties of underwater tail slaps recorded from killer whales in Norway, and thud-like sounds recorded from killer whales in Iceland suggest that Norwegian and Icelandic killer whales use similar hunting techniques. The acoustic characteristics of sounds produced by underwater tail slaps were similar to the ones from other cavitation sound sources described in the literature, both in term of temporal and frequency features as well as in source level. We suggest that multiple factors generated by the tail slaps like particle fluctuations, turbulence, pressure changes and physical impact cause debilitation of herring.

“…Zagaeski (Zagaeski, 1987) showed that a broadband impulse of very high peak pressure of more than 230 dB re. 1 μPa (pp) generated by a spark generator had a debilitating effect on guppies.…”

Section: Discussionmentioning

confidence: 99%

The responses of Atlantic cod (Gadus morhua L.) to ultrasound-emitting predators: stress, behavioural changes or debilitation?

Schack

Malte

Madsen

2008

SUMMARYA previous study has reported that Atlantic cod can be conditioned to detect ultrasonic sound pulses of high intensity. This capability has been proposed as a mean for detection and avoidance of echolocating toothed whales that emit intense ultrasonic clicks. In this study, we use acoustic playbacks to test the hypotheses that unconditioned cod can detect and respond to intense ultrasound from toothed whales and from echosounders. Intense ultrasound exposure of 210 dB re. 1 μPa (pp) did not cause a short-term stress response in the form of bradycardia in unconditioned cod. Free-swimming cod exposed to ultrasonic clicks and echosounder pulses with received levels of more than 204 dB re. 1 μPa (pp) did not elicit flight responses as seen in ultrasound detecting Alosinae. Furthermore, we tested the debilitating effects of high intensity ultrasound on swimming cod with no detected changes in swimming ability when exposed to more than 213 dB re. 1 μPa (pp). It is concluded that intense ultrasound exposure induces neither an antipredator nor a stress response in Atlantic cod, and that echosounder pulses and biosonar clicks therefore most probably play no ecophysiological role in wild cod populations.