Low-Frequency Sound and Marine Mammals Current Knowledge and Research Needs (1994) / Chapter Skim
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3 TOPICS FOR FUTURE RESEARCH
3 TOPICS FOR FUTURE RESEARCH
Pages 40-62
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From page 40... ...
In this chapter the committee identifies several areas in which more research is needed in order to provide a better understanding of the effects of low-frequency sounds on marine mammals and their prey. The next two major sections Behavior of Marine Mammals in the Wild, and Structure and Function of the Auditory System describe several of the proposed studies that focus on the acoustic behavior, disturbance responses, and hearing of marine mammals.
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From page 41... ...
This committee believes that all of the recommendations described below need to be addressed in order to find out how low-frequency sounds affect marine mammals. BEHAVIOR OF MARINE MAMMALS IN THE WILD Aims: To determine the normal behaviors of marine mam mals in the wild and their behavioral responses to human made acoustic signals.
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From page 42... ...
Natural, Ecologically Important Signals Aims: To determine how marine mammals utilize natural sounds for communication and for maintaining their normal behavioral repertoire. It is well known that many marine mammal species utilize sounds for signaling other members of the same species (intraspecific behaviors)
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From page 43... ...
, this information could be used in designing experiments to determine how other sounds might mask or otherwise change a species's perception of intraspecific signaling. Investigations on natural sounds of marine mammals might capitalize on existing hydrophore arrays (e.g., the integrated undersea surveillance discussed in the section on Measurement Techniques below)
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From page 44... ...
Such experiments might use a local population of marine mammals engaged in feeding or breeding activity. The committee suggests using sound sources capable of producing sounds of various sorts, including sounds of high intensity and low frequency.
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From page 45... ...
Further work with additional stimuli and species would reveal whether the deflections observed in migrating gray whales also occur with sounds having spectral characteristics, durations, and duty cycles other than those already tested. Comparisons should be made between the effects observed with stationary and moving sound sources, and between single and multiple, simultaneous sources.
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From page 46... ...
It is known, or believed, that sperm whales, beaked whales, and elephant seals are capable of diving to depths of 1,000 m or below, and that white whales, pilot whales, bottlenose dolphins, Weddell seals, and other species can dive to depths of at least several hundred meters. If intense sounds were present during these dives, the animals would encounter large local variations in sound levels that might alter their behavior during diving and feeding.
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From page 47... ...
Basic Studies of Audiometry Aim: To determine basic hearing capabilities of various species of marine mammals. Audiometric functions show the weakest sounds that an animal can hear over the frequency range to which it is sensitive.
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From page 48... ...
Measurements on Ensnared or Beached Marine Mammals Aim: To determine hearing capabilities of larger marine mam mals that are not amenable to laboratory study. As noted above, very little is known about the hearing and auditory systems of large cetaceans such as baleen and sperm whales.
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From page 49... ...
During the release process, it may be possible to equip the whales with electrophysiological monitoring apparatus and to obtain auditory measurements using evoked-response procedures. Major difficulties with all such work are the background noise present (here due to the release process)
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From page 50... ...
Temporary Threshold Shift Aim: Determine sound-pressure levels that produce temporary and permanent hearing loss in marine mammals. At this time, essentially nothing is known about the auditory aftereffects of exposure to intense sound in marine mammals, fish, or invertebrates.
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From page 51... ...
Thus, were there behavioral habituation to intense sounds, animals might, to their detriment, re-enter regions having dangerously high sound levels, thereby risking additional hearing loss. Presumably, this habituation problem would be most severe in geographical regions associated with feeding, mating, and other strong positive motivations.
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From page 52... ...
Although it is known that the overall structure of the middle and inner ears is similar to that of terrestrial mammals, there are only very limited data on the detailed structure of the cochleae and more peripheral auditory structures. One set of questions concerns how sound actually gets to the inner ear, and whether the pathways differ for different frequencies and/or in various marine mammal groups.
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From page 53... ...
The sensory receptors of fish that are found in the inner ear and lateral line organs the systems involved with detection of acoustic and hydrodynamic signals employ the same type of sensory hair cell as found in the mammalian ear (reviewed in Popper and Pay, 1993; Popper and Platt, 1993~. These cells are potentially subject to the same types of damage from exposure to intense sound as hair cells of the mammalian ear (e.g., Yan et al.
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From page 54... ...
Thus, intense sounds may affect the availability of organisms in the food chain of marine mammals even if these organisms do not have auditory receptors. This committee recommends that research be conducted on the ways in which fishes, squids, and crustaceans (especially Frill)
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From page 55... ...
Tags incorporating additional sensors are a prerequisite for much of the high-priority research on effects of low-frequency sounds on marine mammals in the wild (see the first section in this chapter)
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From page 56... ...
Integrated Undersea Surveillance System (IUSS) Aim: To develop means of using in-place acoustic monitor ing devices to study marine mammal movement and behav ior on an ocean basin scale and of following individuals or groups of animals for extended periods and distances.
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From page 57... ...
are particularly important for developing an understanding of the physiological effects of high-intensity, low-frequency sounds on these animals. One approach to determining some aspects of the hearing capabilities of such species would be to record physiological evoked potentials in response to presentation of acoustic signals (see subsection Measurements on Ensnared or Beached Marine Mammals in the section on the Auditory System)
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From page 58... ...
A broader application would be to develop effective warning signals to protect marine mammals from other potentially harmful activities such as entanglement with fishing gear or collision with ships. REFERENCES Allen, A.R., and A
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From page 59... ...
1983. Investigations of the potential effects of underwater noise from petroleum industry activities on migrating gray whale behavior.
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1975. Auditory brain stem responses in neurological disease.
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From page 61... ...
1975. Underwater hearing sensitivity of two ringed seals (Pusa hispida)
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