Content area
Full Text
J Comp Physiol A (2014) 200:967981 DOI 10.1007/s00359-014-0943-x
ORIGINAL PAPER
Hearing in the sea otter (Enhydra lutris): auditory proles for an amphibious marine carnivore
Asila Ghoul Colleen Reichmuth
Abstract In this study we examine the auditory capabilities of the sea otter (Enhydra lutris), an amphibious marine mammal that remains virtually unstudied with respect to its sensory biology. We trained an adult male sea otter to perform a psychophysical task in an acoustic chamber and at an underwater apparatus. Aerial and underwater audiograms were constructed from detection thresholds for narrowband signals measured in quiet conditions at frequencies from 0.12540 kHz. Aerial hearing thresholds were also measured in the presence of octave-band masking noise centered at eight signal frequencies (0.2522.6 kHz) so that critical ratios could be determined. The aerial audiogram of the sea otter resembled that of sea lions and showed a reduction in low-frequency sensitivity relative to terrestrial mustelids. Best sensitivity was 1 dB re 20 Pa
at 8 kHz. Under water, hearing sensitivity was signicantly reduced when compared to sea lions and other pinniped species, demonstrating that sea otter hearing is primarily adapted to receive airborne sounds. Critical ratios were more than 10 dB higher than those measured for pinnipeds, suggesting that sea otters are less efcient than other marine carnivores at extracting acoustic signals from background noise, especially at frequencies below 2 kHz.
Keywords Sea otter Hearing Audiogram Masking Critical ratio
Received: 2 July 2014 / Revised: 10 September 2014 / Accepted: 12 September 2014 / Published online: 24 September 2014 Springer-Verlag Berlin Heidelberg 2014
Introduction
Sea otters (Enhydra lutris) are coastal-living marine mammals with a unique life historywhile they forage under water on benthic invertebrates, they perform necessary biological functions relating to communication, reproduction, and thermoregulation primarily at the waters surface.Remarkably little is known about the sensory biology of sea otters. Observations suggest that they use a combination of environmental cues to perform critical behaviors (Kenyon 1969; Hines and Loughlin 1980; Kvitek et al. 1991).However, the extent to which their senses are adapted for amphibious living is poorly described.
Sea otters are one of several mustelid carnivores to adopt an aquatic lifestyle, but only one of two extant species (sea otter and marine otter, Lontra felina) to inhabit the marine environment. In...