Blue Whales and Man Made Noise
Blue whale vocal behavior is affected by man-made noise, even when that noise does not overlap the frequencies the whales use for communication, according to new research published Feb. 29 in the open access journal PLoS ONE. The whales were less likely to emit calls when mid-frequency sonar from ships was present, but were more likely to do so when ship sounds were nearby, the researchers report. The data show an acoustical response from blue whales to MFA sonar and ship noise. In particular, there is a disruption of the D call production of these animals with MFA sonar. The implications of such a response are unknown to date, but owing to the low received level, a single source of MFA sonar may be capable of affecting the animals' vocal behavior over a substantial area. Additionally, nearby ships elicit more intense D calling by blue whales.
The use of sound for whale communication and acquisition of information about the environment has evolved across the years and constitutes an important aspect of baleen whale behavior. Given the increasing level of anthropogenic (human) noise in the ocean, there has been concern that high-intensity anthropogenic noise may impact communication and other behaviors involving whale sound production.
Estimates made by Cummings and Thompson (1971) suggest the source level of sounds made by blue whales are between 155 and 188 decibels when measured relative to a reference pressure of one micropascal at one meter. All blue whale groups make calls at a fundamental frequency between 10 and 40 Hz; the lowest frequency sound a human can typically perceive is 20 Hz. Blue whale calls last between ten and thirty seconds.
The reason for blue whale vocalization is unknown. Richardson in 1995 discussed six possible reasons:
Maintenance of inter-individual distance
Species and individual recognition
Contextual information transmission (for example feeding, alarm, courtship)
Maintenance of social organization
Location of topographic features
Location of prey resources
For further information: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0032681#s3