Depth dependent variation of the echolocation pulse rate of bottlenose dolphins (Tursiops truncatus).
Trained odontocetes appear to have good control over the timing (pulse rate) of their echolocation clicks; however, there is comparatively little information about how free-ranging odontocetes modify their echolocation in relation to their environment. This study investigates echolocation pulse rate in 14 groups of free-ranging bottlenose dolphins (Tursiops truncatus) at a variety of depths (2.4-30.1 m) in the Gulf of Mexico. Linear regression models indicated a significant decrease in mean pulse rate with mean water depth. Pulse rates for most groups were multi-modal. Distance to target estimates were as high as 91.8 m, assuming that echolocation was produced at a maximal rate for the target distance. A 5.29-ms processing lag time was necessary to explain the pulse rate modes observed. Although echolocation is likely reverberation limited, these results support the hypotheses that free-ranging bottlenose dolphins in this area are adapting their echolocation signals for a variety of target detection and ranging purposes, and that the target distance is a function of water depth.
Simard
Peter
P
College of Marine Science, University of South Florida, 140 7th Avenue South, St Petersburg, Florida 33701, USA. psimard@mail.usf.edu
Hibbard
Ashley L
AL
McCallister
Kimberly A
KA
Frankel
Adam S
AS
Zeddies
David G
DG
Sisson
Geoffrey M
GM
Gowans
Shannon
S
Forys
Elizabeth A
EA
Mann
David A
DA
D000162:Acoustics; D000818:Animals; D000835:Animals, Wild; D001267:Atlantic Ocean; D050681:Bottle-Nosed Dolphin; D004455:Echolocation; D004777:Environment; D005431:Florida; D016018:Least-Squares Analysis; D016014:Linear Models; D013997:Time Factors