Biology Reference
In-Depth Information
6.12 Acoustic Masking in Freshwater Ecosystems
In the aquatic environment, the acoustic cues are important characteristics for the
survival of animals. Sound travels fast in the aquatic medium and more information
is carried when compared with the terrestrial ecosystems. In shallow waters, the
sound produced by aquatic insects has a range of approximately 1 m, which is quite
different when compared with terrestrial insects that have a communication range
of at least many meters (Aiken
1982
).
In fish communities there are species considered specialists with enhanced
auditory sensitivity and broad frequency ranges and non-specialists (or generalists)
that do not have such characters. Specialists seem have evolved in quiet habitats
such as the deep sea, lakes, backwaters of rivers, and slowly flowing streams. This
hypothesis has been confirmed after an experimentation conducted by Amoser and
Ladich (
2005
) in four different freshwater habitats near Vienna, Austria (Danube
River, Triesting stream, Lake Neusiedl, backwaters of the Danube River). The sonic
signature of these aquatic systems were played back to an hearing specialist, the
common carp (
Cyprinus carpio
), and a hearing generalist, the European perch
(
Perca fluviatilis
). Results have confirmed that carp hearing is only partially masked
by a quiet sonic environment (mean threshold, 9 dB) but is heavily masked by stream
and river noise by up 49 dB in the hearing range 0.5-1.0 kHz. In contrast, perch
auditory capacity is not impacted by the noise of all habitats.
6.13 Acoustic Masking in Marine Ecosystems
The increase of human intrusion in the marine ecosystem has been accompanied by
noise intrusion with important effects of masking for marine animal communica-
tion. This physical process has important consequences for the life of pelagic
mammals, as recently stressed by Clark et al. (
2009
), who proposed a model to
quantify changes of animal communication space as a result of spatial, spectral, and
temporal changes in background noise. They provided a sonar equation to calculate
time-varying spatial maps of potential communication masking according to the
frequency bands considered (Fig.
6.10
).
Pile-driving activity during the construction of bridges or offshore windfarms
represents an important source of disturbance to water life. In particular, Bailey
et al. (
2010
) have measured the sound produced by pile-driving activity at a
distance from 0.1 to 80 km. They found that for the bottlenose dolphins, auditory
injury would only have occurred within 100 m from the pile driving, but behavioral
modification are expected to occur up to 50 km away.
Acoustic measurements were carried out also by Erbe (
2009
) during the con-
struction of the duplicate Houhton Highway bridge in western Moreton Bay,
Queensland (Australia). This area is a protected marine park and a World Heritage
site of the Ramsar Wetland where turtles, dugong, sharks, dolphins, and whales are
common. This author has not found evident damage to marine fauna but has
observed a low abundance of marine fauna close to the pile-driving activity.
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