Publications

Abstract

Manatees live in shallow, frequently turbid
waters. The sensory means by which they navigate in these
conditions are unknown. Poor visual acuity, lack of echo-
location, and modest chemosensation suggest that other
modalities play an important role. Rich innervation of sen-
sory hairs that cover the entire body and enlarged soma-
tosensory areas of the brain suggest that tactile senses are
good candidates. Previous tests of detection of underwater
vibratory stimuli indicated that they use passive movement
of the hairs to detect particle displacements in the vicinity
of a micron or less for frequencies from 10 to 150 Hz. In
the current study, hydrodynamic stimuli were created by
a sinusoidally oscillating sphere that generated a dipole
field at frequencies from 5 to 150 Hz. Go/no-go tests of
manatee postcranial mechanoreception of hydrodynamic
stimuli indicated excellent sensitivity but about an order of
magnitude less than the facial region. When the vibrissae
were trimmed, detection thresholds were elevated, suggest-
ing that the vibrissae were an important means by which
detection occurred. Manatees were also highly accurate in two-choice directional discrimination: greater than 90%
correct at all frequencies tested. We hypothesize that mana-
tees utilize vibrissae as a three-dimensional array to detect
and localize low-frequency hydrodynamic stimuli