[MARMAM] New publications on odontocete hearing and soundscapes

Aran Mooney amooney at whoi.edu
Wed Jun 20 03:39:32 PDT 2018

New publications on odontocete hearing and soundscapes

We are pleased to announce two new publications on hearing in wild 
belugas, variation within a population, and a comparison to natural 
noise in their soundscapes. Abstracts and information on accessing the 
articles can be found below.

Mooney, T.A., Castellote, M., Quakenbush, L., Hobbs, R., Gaglione, E. 
and Goertz, C., 2018. Variation in hearing within a wild population of 
beluga whales (Delphinapterus leucas). Journal of Experimental Biology, 
221(9), p.jeb171959. doi: 10.1242/jeb.171959.

The article can be found here: https://doi.org/10.1242/jeb.171959 or by 
contacting Aran Mooney at amooney at whoi.edu

Abstract:  Documenting hearing abilities is vital to understanding a 
species’ acoustic ecology and for predicting the impacts of increasing 
anthropogenic noise. Cetaceans use sound for essential biological 
functions such as foraging, navigation and communication; hearing is 
considered to be their primary sensory modality. Yet, we know little 
regarding the hearing of most, if not all, cetacean populations, which 
limits our understanding of their sensory ecology, population level 
variability and the potential impacts of increasing anthropogenic noise. 
We obtained audiograms (5.6–150 kHz) of 26 wild beluga whales to measure 
hearing thresholds during capture–release events in Bristol Bay, AK, 
USA, using auditory evoked potential methods. The goal was to establish 
the baseline population audiogram, incidences of hearing loss and 
general variability in wild beluga whales. In general, belugas showed 
sensitive hearing with low thresholds (<80 dB) from 16 to 100 kHz, and 
most individuals (76%) responded to at least 120 kHz. Despite belugas 
often showing sensitive hearing, thresholds were usually above or 
approached the low ambient noise levels measured in the area, suggesting 
that a quiet environment may be associated with hearing sensitivity and 
that hearing thresholds in the most sensitive animals may have been 
masked. Although this is just one wild population, the success of the 
method suggests that it should be applied to other populations and 
species to better assess potential differences. Bristol Bay beluga 
audiograms showed substantial (30–70 dB) variation among individuals; 
this variation increased at higher frequencies. Differences among 
individual belugas reflect that testing multiple individuals of a 
population is necessary to best describe maximum sensitivity and 
population variance. The results of this study quadruple the number of 
individual beluga whales for which audiograms have been conducted and 
provide the first auditory data for a population of healthy wild 

T. Aran Mooney, Manuel Castellote, Ian T. Jones, Lori Quakenbush, 
Roderick Hobbs, Eric Gaglione, Caroline Goertz. 2018. Local acoustic 
habitat relative to hearing sensitivities in beluga whales 
(Delphinapterus leucas). Journal of Ecoacoustics. 2, 

This is a free-open access article. Download it here: 
https://doi.org/10.22261/JEA.QZD9Z5 and feel free to contact Aran Mooney 
with any questions at: amooney at whoi.edu

Abstract:   Background noise can have a substantial effect on 
communication signals, however far less is known about how natural 
soundscapes may influence hearing sensitivity. Here we compare the 
audiograms of 26 wild beluga whales measured in their natural 
environment to a series of ecoacoustic measurements within a primary 
portion of their Bristol Bay summer habitat, the Nushagak Estuary in 
Bristol Bay, AK, USA. Environmental acoustic measurements were made 
during 2012 and 2016 using two different methods: a moored recorder and 
drifter buoys. Environmental noise curves varied substantially. Drifter 
recordings from the middle of Nushgak Estuary had the highest spectrum 
levels during ebb tides with acoustic energy from sediment transport 
extending well into higher frequencies (ca. 60 kHz), likely due to 
rapidly moving tidal flow and shifting sediment in that location. 
Drifter recordings near the estuary mouth and shallow tidal flats were 
lower amplitude. Noise levels generally varied during drifts (in one 
case up to ca. 6 dB) reflecting acoustic cues available to the local 
belugas. The moored recorder showed a substantially different spectral 
profile, especially at lower frequencies, perhaps due to its attachment 
to a pier piling and subsequent pier noise. Hearing sensitivity varied 
by individual and thresholds often fell above 1/3 octave-band noise 
levels, but not overall noise spectral density. Audiograms of the most 
sensitive animals closely paralleled the lowest ambient noise power 
spectral density curves, suggesting that an animal’s auditory dynamic 
range may extend to include its habitat’s quietest conditions. These 
data suggest a cautious approach is necessary when estimating the 
sound-sensitivity of odontocetes found in quiet environments as they may 
have sensitive auditory abilities that allow for hearing within the 
lowest noise-level conditions. Further, lower level ambient noise 
conditions could provide a conservative estimate of the maximal 
sensitivity of some cetacean populations within specific environments.

BioAcoustics and Sensory Ecology (BASE) Lab
Biology Department
Woods Hole Oceanographic Institution

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