Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
Figure 2.25. Underwater Audiograms of Several Odontocetes: (A) Uhite Whale
(Uhite et al. 1978; Awbrey et al. 1988); Killer Whale (Hall and
Johnson 1972); Harbor Porpoise (Andersen 1970); (B) Bottlenose
Dolphin (Johnson 1968a; Ljungblad et al. 1982~); Amazon River
Dolphin or Boutu (Jacobs and Hall 1972); False Killer Whale
. (Thomas et a1 . 1978).
For each species there is a range of frequencies where hearing thresholds
are low. Below and above this range the hearing thresholds increase with
decreasing or increasing frequency. The increase in thresholds is rather
gradual at low frequencies. It is possible that estimated auditory thresholds
for many species are too high for frequencies below 1-10 kHz, since the small
tanks in which most audition tests have been done may have many echoes,
standing waves and otherwise elevated noise levels. This problem was
suspected in the studies by Hall and Johnson (1972), Jacobs and Hall (1972)
and Ljungblad et al. (1982). The limited and questionable data on sensitivity
at low frequencies (