There is increasing concern about the effects of pile driving and other anthropogenic (human-generated) sound on fishes. Although there is a growing body of reports examining this issue, little of the work is found in the peer-reviewed literature. This review critically examines both the peer-reviewed and 'grey' literature, with the goal of determining what is known and not known about effects on fish. A companion piece provides an analysis of the available data and applies it to estimate noise exposure criteria for pile driving and other impulsive sounds. The critical literature review concludes that very little is known about effects of pile driving and other anthropogenic sounds on fishes, and that it is not yet possible to extrapolate from one experiment to other signal parameters of the same sound, to other types of sounds, to other effects, or to other species.
In order to determine excitation patterns to the lateral line system from a nearby 50 Hz oscillating sphere, dipole flow field equations were used to model the spatial distribution of pressures along a linear array of lateral line canal pores. Modeled predictions were then compared to pressure distributions measured for the same dipole source with a miniature hydrophone placed in a small test tank used for neurophysiological experiments. Finally, neural responses from posterior lateral line nerve fibers in the goldfish were measured in the test tank to demonstrate that modeled and measured pressure gradient patterns were encoded by the lateral line periphery. Response patterns to a 50 Hz dipole source that slowly changed location along the length of the fish included (1) peaks and valleys in spike-rate responses corresponding to changes in pressure gradient amplitudes, (2) 180 degrees phase-shifts corresponding to reversals in the direction of the pressure gradient and (3) distance-dependent changes in the locations of peaks, valleys and 180 degrees phase-shifts. Modeled pressure gradient patterns also predict that the number of neural amplitude peaks and phase transitions will vary as a function of neuromast orientation and axis of source oscillation. The faithful way in which the lateral line periphery encodes pressure gradient patterns has implications for how source location and distance might be encoded by excitation patterns in the CNS. Phase-shift information may be important for (1) inhibitory/excitatory sculpting of receptive fields and (2) unambiguously encoding source distance so that increases in source distance are not confused with decreases in source amplitude.
There is growing international concern about the effects of human-generated sound on fish and other aquatic organisms. However, because of a striking paucity of well-designed and controlled experimental data, very little is actually known about the effects of these sounds on fish. Findings suggest that human-generated sounds, even from very high intensity sources, might have no effect in some cases or might result in effects that range from small and temporary shifts in behavior all the way to immediate death. At this point, however, it is nearly impossible to extrapolate from results with one sound source, one fish species, or even fish of one size to other sources, species, or fish sizes. The present paper briefly discusses the potential effects of sound on fish, describes some of the more recent well-controlled experimental studies, and points out areas for future study that will be needed before a real understanding of the effects of sound on fish can be developed.
Fish (Astronotus ocellatus, the oscar) were subject to pure tones in order to determine the effects of sound at levels typical of man-made sources on the sensory epithelia of the ear and the lateral line. Sounds varied in frequency (60 or 300 Hz), duty cycle (20% or continuous), and intensity (100, 140, or 180 dB re: 1 muPa). Fish were allowed to survive for 1 or 4 days posttreatment. Tissue was then evaluated using scanning electron microscopy to assess the presence or absence of ciliary bundles on the sensory hair cells on each of the otic endorgans and the lateral line. The only damage that was observed was in four of five fish stimulated with 300-Hz continuous tones at 180 dB re: 1 muPa and allowed to survive for 4 days. Damage was limited to small regions of the striola of the utricle and lagena. There was no damage in any other endorgan, and the size and location of the damage varied between specimens. No damage was observed in fish that had been allowed to survive for 1 day poststimulation, suggesting that damage may develop slowly after exposure.
The authors previously reported that American shad (Alosa sapidissima) can detect sounds from 100 Hz to 180 kHz, with two regions of best sensitivity, one from 200 to 800 Hz and the other from 25 to 150 kHz [Mann et al., Nature 389, 341 (1997)]. These results demonstrated ultrasonic hearing by shad, but thresholds at lower frequencies were potentially masked by background noise in the experimental room. In this study, the thresholds of the American shad in a quieter and smaller tank, as well as thresholds for detecting stimulated echolocation sounds of bottlenosed dolphins was determined. Shad had lower thresholds for detection (from 0.2 to 0.8 kHz) in the quieter and smaller tank compared with the previous experiment, with low-frequency background noise but similar thresholds at ultrasonic frequencies. Shad were also able to detect echolocation clicks with a threshold of 171 dB re: 1 microPa peak to peak. If spherical spreading and an absorption coefficient of 0.02 dB/m of dolphin echolocation clicks are assumed, shad should be able to detect echolocating Tursiops truncatus at ranges up to 187 m. The authors propose that ultrasonic hearing evolved in shad in response to selection pressures from echolocating odontocete cetaceans.
In order to determine unambiguously the bearing of a sound source, a fish must be able to resolve acoustic pressure and the components of the acoustic displacement vector from the signals detected by the otolithic organs. A new hypothesis for the processing of acoustical information by bony fish is presented. It is demonstrated that much of the processing required to do this may be implicit in the structure of the ear and its associated neural innervation. Possible algorithms are presented that the central nervous system might use to further process the derived information to localize a sound source and discriminate frequency and range. The hypothesis is shown to be consistent with much of what is known of the morphology and physiology of the auditory system of bony fishes.
SUMMARYIt has recently been shown that a few fish species, including American shad(Alosa sapidissima; Clupeiformes), are able to detect sound up to 180 kHz, an ability not found in most other fishes. Initially, it was proposed that ultrasound detection in shad involves the auditory bullae, swim bladder extensions found in all members of the Clupeiformes. However, while all clupeiformes have bullae, not all can detect ultrasound. Thus, the bullae alone are not sufficient to explain ultrasound detection. In this study, we used a developmental approach to determine when ultrasound detection begins and how the ability to detect ultrasound changes with ontogeny in American shad. We then compared changes in auditory function with morphological development to identify structures that are potentially responsible for ultrasound detection. We found that the auditory bullae and all three auditory end organs are present well before fish show ultrasound detection behaviourally and we suggest that an additional specialization in the utricle(one of the auditory end organs) forms coincident with the onset of ultrasound detection. We further show that this utricular specialization is found in two clupeiform species that can detect ultrasound but not in two clupeiform species not capable of ultrasound detection. Thus, it appears that ultrasound-detecting clupeiformes have undergone structural modification of the utricle that allows detection of ultrasonic stimulation.
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