The following article appeared in the most recent issue if the Journal
of Mammalogy, and can be downloaded at
http://www.uvm.edu/~bmitchel/Bioacoustics.html:
Tyack, Peter L. Implications for marine mammals of large-scale changes
in the marine acoustic environment. Journal of Mammalogy, 89(3):549-558.
Abstract: The amount of underwater sound from ship traffic, commercial,
research, and military sound sources has increased significantly over
the past century. Marine mammals and many other marine animals rely on
sound for short- and long-range communication, for orientation, and for
locating prey. This reliance has raised concern that elevated sound
levels from human sources may interfere with the behavior and physiology
of marine animals. The dominant source of human sound in the sea stems
from propulsion of ships. Shipping noise centers in the 20- to 200-Hz
band. Frequencies this low propagate efficiently in the sea, and
shipping has elevated the global deepwater ambient noise 10- to 100-fold
in this frequency band. Baleen whales use the same frequency band for
some of their communication signals, and concern has been raised that
elevated ambient noise may reduce the range over which they can
communicate. Marine mammals have a variety of mechanisms to compensate
for increased noise, but little is known about the maximum range at
which they may need to communicate. Some of the most intense human
sources of sound include air guns used for seismic exploration and sonar
for military and commercial use. Human sources of sound in the ocean can
disturb marine mammals, evoking behavioral responses that can
productively be viewed as similar to predation risk, and they can
trigger allostatic physiological responses to adapt to the stressor.
Marine mammals have been shown to avoid some human sound sources at
ranges of kilometers, raising concern about displacement from important
habitats. There are few studies to guide predictions of when such
changes start to lower the fitness of individuals or have negative
consequences for the population. Although acute responses to intense
sounds have generated considerable interest, the more significant risk
to populations of marine mammals is likely to stem from less visible
effects of chronic exposure.
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