Ocean Noise and Marine Mammals (2003) / Chapter Skim
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3. Effects of Noise on Marine Mammals
3. Effects of Noise on Marine Mammals
Pages 83-108
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From page 83... ...
HEARING CAPABILITIES OF MARINE ORGANISMS Marine Mammals Hearing research has traclitionally focused on mechanisms of hearing loss in humans. Animal research has therefore emphasized experimental 83
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From page 84... ...
The same reasons that make marine mammals acoustically and auditorally interesting that is, that they are a functionally exceptional anal an aquatic ear also make them difficult research subjects. Some issues about marine mammal hearing can be addressed both directly and inferentially from the data at hand.
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From page 85... ...
Since many forms of hearing loss are based in physical structure of the inner ear, it is likely hearing damage occurs by similar mechanisms in both land and marine mammal ears. On the other hand, the sea is not, nor was it ever, even primordially silent.
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From page 86... ...
Little information exists to describe how marine mammals respond ~ohvsicaliv and behaviorally to intense sounds and to long-term increases in ambient noise levels. The data available show that all marine mammals have a fundamentally mammalian ear, which through adaptation to the marine environment has developed broader hearing ranges (Figure 1-1)
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From page 87... ...
To summarize, marine mammals as a group have functional hearing ranges of 10 Hz to 200 kHz. They can be divided into infrasonic balacnids (probable functional ranges of 15 Hz to 20 kHz; good sensitivity from 20 Hz to 2 kHz)
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From page 88... ...
Hearing capabilities in several fish species and a shark showing the lowest sound level that an animal can detect at each frequency. It is important to note that while thresholds here are presented in units of pressure, it is very likely that a number of species, including the sharks, respond best to particle acceleration and had experiments been done in terms of acceleration the shapes of the hearing curves might be somewhat different, though it is likely that the range of detection would not change very much.
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From page 89... ...
There is some additional evidence from attempts at behavioral studies and from recordings of responses of the inner ear, but no data suggest higher frequencies of hearing. ACOUSTIC TRAUMA IN MARINE MAMMALS Recent reports and retrospectively analyzed data show an association between the use of multiple high-energy mid-range sonars and mass strandings of beaked whales (Ziphius cavirostris)
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From page 90... ...
Behavioral responses range from subtle changes in surfacing and breathing patterns, to cessation of vocalizations, to active avoidance or escape from the region of the highest sound levels. Typical changes in cetacean response to anthropogenic noise are summarized from several studies of bowhead whales as shorter surfacings, shorter dives, fewer blows per surfacing, and longer intervals between successive blows (Richardson et al., 1995~.
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From page 91... ...
Beluga whales adjust their echolocation clicks to higher frequencies and to higher source levels in the presence of background noise (Au et al., 1985~. Miller et al.
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From page 92... ...
During spring migration, when the only available lead was within 200 m of a projector playing sounds associated with a drilling platform, the bowheads continued through a sound field with received levels of 131 dB re 1 Spa (Richardson et al., 1991~. Age and Sex Some age and sex classes are more sensitive to noise disturbance, and such disturbance may be more detrimental to young animals.
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From page 93... ...
Bowhead whales in shallow water are more responsive to the overflights of aircraft than are bowheads in deeper water (Richardson and Malme, 1993~. Beluga whales are more sensitive to ship noise when they are confined to open-water leads in the ice in the spring (Burns and Seaman, 1985~.
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From page 94... ...
However, when the source was located seaward of the migratory path, the whales ignored source levels of 200 dB re 1 Spa at 1 m and received levels greater than 140 dB re 1 Spa (Tyack and Clark, 1998~. Variability of Responses The range of variability of responses of marine mammals to anthropogenic noise and other disturbances can be summarized in the responses of beluga whales to ships.
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From page 95... ...
On the other hand, in Bristol Bay beluga whales continue to feed when surrounded by fishing vessels and resist dispersal even when purposely harassed by motorboats (Fish and Vania, 1971~. Thus, depending on habitat, demography, prior experience, activity, resource availability, sound transmission characteristics, behavioral state, and ever-present individual variability, the response of beluga whales can range from the most sensitive reported for any species to ignoring of intenBeluga whales also show the full range of revues of tional harassment.
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From page 96... ...
MASKING OF ACOUSTIC CUES BY MARINE NOISE One of the most pervasive and significant effects of a general increase in background noise on most vertebrates, including marine mammals, may be the reduction in an animal's ability to detect relevant sounds in the presence of other sounds a phenomenon known as masking. Masking, which might be thought of as acoustic interference, occurs when both the signal and masking noise have similar frequencies and either overlap or occur very close to each other in time.
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From page 97... ...
EFFECTS OF NOISE ON MARINE MAMMALS a 80 70 60 50 40 1 1 m 30 20 i: · Beluga Whale Bottlenose Dolphin 1 Bottlenose Dolphin 2 False Killer Whale Human - , 1 00 1 ,000 1 0,000 1 00,000 1 ,000,000 Frequency (Hz) b 80 70 60 50 404 ' 30 20 10 O ~~a ° Elephant Seal · Harbour Seal ~ Ringed Seal · Northern Fur Seal Harp Seal · Common Seal 0 California Sealion · Human 1 hi\ ~ · — 1 00 1 ,000 1 0,000 1 00,000 Frequency (Hz)
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From page 98... ...
In contrast to the pure tone signal results, when the signal was of biological relevance, that is, killer whale vocalizations, there was little evidence of masking by boat noise. Concern about interference with beluga whales' communication by icebreaking activity led Erbe and co-workers to explore masking of a beluga call by three different types of icebreaker noise (Erbe, 1997, 2000; Erbe and Farmer, 1998; Erbe et al., 1999~.
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From page 99... ...
If marine mammals attend to barely detectable signals, then any increase in noise may contribute to masking. The zone of masking is defined by the range at which sound levels from the noise source are received above threshold within the CB centered on the signal.
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From page 100... ...
For example, the vocal output of a beluga whale changed when it was moved to a location with higher levels of continuous background noise (Au et al., 1985~. In the noisier environment, the animal increased both the average level and frequency of its vocalizations, as though it were trying to compensate for and avoid the masking effects of, the increased, predominantly low-frequency, background noise levels.
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From page 101... ...
Beluga whales increased call repetition and shifted to higher peak frequencies in response to boat traffic (Lesage et al., 1999~. Gray whales increased the amplitude of their vocalizations, changed the timing of vocalizations, and used more frequency-modulated signals In noisy environments (Dah~heim, 1987~.
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From page 102... ...
Detailed field research involving fine-scale behavioral observations linked to sensitive real-time acoustic monitoring will be required to gain any appreciation of how marine mammals utilize these lowlevel noises. To investigate the occurrence of masking in the real world, field projects could be designed to study behavioral changes, thought to be indicative of masking (such as the strategies to avoid masking outlined earlier)
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From page 103... ...
but also because of a change in seal behavior in which the animals spend more time swimming with their heads out of the water when they are in intense sound fields. Seals and California sea lions (Zalophus californianus)
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From page 104... ...
In fact, residency time was greater in the bay closest to the blast site than it was in other bays of equivalent size and productivity nearby. Estimated peak received levels during blasting were approximately 153 dB re 1,uPa with most of the sound energy below 1,000 Hz (Todd et al., 1996~.
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From page 105... ...
but have not shown any evidence of physiological effects in any of the blood chemistry parameters measured. Beluga whales exposed for 30 min to 134-153 dB re 1 Spa playbacks of noise with a synthesized spectrum matching that of a semisubmersible oil platform (Thomas et al., 1990)
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From page 106... ...
Finally, radio tags need to be developed that remain attached for several years and transmit only on a programmed cycle or in response to a query signal. For most marine mammal species, the difficulty in identifying individual animals rapidly and reliably makes it very difficult to follow animals for long periods of time to determine cumulative effects.
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From page 107... ...
There are also data that suggest that there may be significant impacts on fish behavior from air-guns, and perhaps from other sound sources. Several studies suggest that intense sounds may result in fish moving from 2While the sensory cells of the ears of fishes and marine mammals are the same, regeneration of damaged cells does not occur in mammals.
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From page 108... ...
Movement of fish from a feeding area of marine mammals (or fishing areas for humans) could have an adverse impact on the higher members of a food chain and therefore have long-term implications despite the fish themselves not being killed or maimed.
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