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lower than the level at which the hearing system of whales could be damaged.
For instance, the sound produced by an adult ranges between 170 and 175 dB re
1
Pa at 1 m, which is lower than the noise produced by some investigated boats
(120 dB at 91 m). Some changes in behavior have been observed with the arrival of
boats close to the whales but is difficult to assess precisely what causes the changes,
whether noise or simply the visual cues.
Parks et al. (
2007
) have discussed the effects of noise on acoustic communication
in right whales (
Eubalena glacialis
and
E. australis
) exposed to an increased level of
ambient noise. In the right whale, an increase of ambient noise level is accompanied
by a lower rate call to avoid a masking effect from low-frequency noise.
Changes in behavior has been observed in the manatee (
Trichechus manatus
latirostris
) by Miksis-Olds and Wagner (
2011
). This species when the ambient
noise is high spends more time feeding and less time milling (undirected move-
ment). The increased foraging activity can be explained as an attempt to meet
nutritional requirements in the shortest time possible when experiencing noise
disturbance that could be considered a menace or a dangerous situation.
In the bottlenose dolphin, Buckstaff (
2004
) has found a different whistling
frequency when boats were approaching, and whistles were more frequent at the
beginning of vessel approach. This modification in the frequency of whistles can
be caused by the necessity of animals to come close together but also to compensate
for the masking effect on communication as the boat approaches.
In
Gobius cruentatus
(Gobiidae), experiments conducted by Sebastianutto
et al. (
2011
) have demonstrated that when males were tested in a round-robin
design during the playback of a field-recorded diesel engine noise residents were
more submissive and won less encounters than in control (silent) conditions.
In the Caribbean hermit crab (
Coenobita clypeatus
), the noise produced by a
boat seems to reduce the attention paid toward potential predators, as confirmed by
an experiment conducted by Chan et al. (
2010
) to verify the hypothesis that ambient
noise has an impact on predatory risk. Boat noise playback was able to distract
hermit crabs and allowed approaching the crabs more closely.
Anthropogenic noise can produce severe effects not only on behavior of pelagic
fishes but also on fish ears, as demonstrated by McCauley et al. (
2003
)in
experiments conducted on the pink snapper (
Pagrus auratus
), in which the hair
cells became damaged after exposure to air-gun noise.
μ
6.15 Effect of Traffic Noise on Wildlife
Roads are important infrastructures worldwide, with an increased impact on the
environment for habitat fragmentation, chemical and sonic pollution, and mortality
from collisions of vehicles with animals. Transportation infrastructures are expo-
nentially increasing around urban areas, affecting many ecosystem processes
(Forman et al.
2003
).
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