Amphibious hearing in ringed seals (Pusa hispida): underwater audiograms, aerial audiograms and critical ratio measurements

Abstract

Ringed seals (Pusa hispida) are semi-aquatic marine mammals with a circumpolar Arctic distribution. In this study, we investigate the amphibious hearing capabilities of ringed seals to provide auditory profiles for this species across the full range of hearing. Using psychophysical methods with two trained ringed seals, detection thresholds for narrowband signals were measured under quiet, carefully controlled environmental conditions to generate aerial and underwater audiograms. Masked underwater thresholds were measured in the presence of octave-band noise to determine critical ratios. Results indicate that ringed seals possess hearing abilities comparable to those of spotted seals (Phoca largha) and harbor seals (Phoca vitulina), and considerably better than previously reported for ringed and harp seals. Best sensitivity was 49 dB re. 1 µPa (12.8 kHz) in water, and −12 dB re. 20 µPa (4.5 kHz) in air, rivaling the acute hearing abilities of some fully aquatic and terrestrial species in their respective media. Critical ratio measurements ranged from 14 dB at 0.1 kHz to 31 dB at 25.6 kHz, suggesting that ringed seals -like other true seals -can efficiently extract signals from background noise across a broad range of frequencies. The work described herein extends similar research on amphibious hearing in spotted seals recently published by the authors. These parallel studies enhance our knowledge of the auditory capabilities of ice-living seals, and inform effective management strategies for these and related species in a rapidly changing Arctic environment.

Active touch in sea otters: in-air and underwater texture discrimination thresholds and behavioral strategies for paws and vibrissae

“…The sea otter's supra-threshold decision times for either paw or vibrissal discrimination were comparable to those for auditory signal detection in phocids (Sills et al, 2014(Sills et al, , 2015, visual discrimination in humans (Kirchner and Thorpe, 2006) and size discrimination in harbor seals (Grant et al, 2013). However, the sea otter's near-threshold decision times were 1.5-to 3-fold faster (Kirchner and Thorpe, 2006;Sills et al, 2014Sills et al, , 2015. At the extreme, the sea otter performed at least 15-fold faster than manatees in a comparable texture discrimination task across all tested levels (Bauer et al, 2012).…”

Amphibious hearing in a diving bird, the great cormorant (Phalacrocorax carbo sinensis)

“…5A). True seals, which are considered to be fully adapted for hearing in both media, have their underwater BF above the in-air BF, and the highfrequency slope is steeper in the underwater than in the in-air audiogram (Reichmuth et al, 2013;Sills et al, 2014Sills et al, , 2015. In fact, the weaker slopes of the average underwater threshold curve and its slightly lower frequency emphasis are more like those of another not aquatically adapted vertebrate, namely humans (Parvin and Nedwell, 1995).…”

Underwater hearing and communication in the endangered Hawaiian monk seal Neomonachus schauinslandi

“…The available hearing data for the Monachinae subfamily includes audiograms for the northern elephant seal (n = 1;Kastak & Schusterman 1999) and the Hawaiian monk seal (n = 1;Thomas et al 1990); note that dashes at the edges of theThomas et al (1990) audiogram depict preliminary data. Representative audiograms are provided for seals in the Phocinae subfamily as thin lines for bearded (n = 2; Sills et al 2020), ringed (n = 1;Sills et al 2015), spotted (n = 2;Sills et al 2014), and harbor seals (n = 2;Kastelein et al 2009). (C) For reference, Kekoa's audiogram is shown with the recently updated Phocid Carnivores in Water (PCW) group audiogram proposed byFinneran (2016), National Marine Fisheries Service (2018), andSouthall et al (2019)…”