Audiogram of a formerly stranded long-finned pilot whale (Globicephala melas) measured using auditory evoked potentials

Abstract

SUMMARYLong-finned pilot whales are highly social odontocetes found in temperate and subpolar regions. This species is particularly known for its interaction with fisheries as well as its mass strandings. Recent tagging work has provided some information about pilot whales in the wild but, even though they have been successfully kept in captivity, little is known about their sensory capabilities. This study investigates the hearing abilities of a rehabilitated 2year old male long-finned pilot whale. A complete audiogram was collected using auditory evoked potential techniques that included measurements of nine frequencies from 4 to 100kHz presented as sinusoidally amplitude-modulated tones. The results indicated that the region of best hearing was between 11.2 and 50kHz and the subject had relatively poor high frequency hearing compared with other odontocete species. This study emphasizes the importance of collecting basic hearing measurements from new species, understanding diagnostic life histories as well as continuously increasing the sample size of audiometry measurements within and between odontocete species as animals become available.

Evoked-potential audiogram of an Indo-Pacific humpback dolphin (Sousa chinensis)

“…Each pip train was 20ms in duration followed by a silence of 30ms so that the sound stimuli were presented at a rate of 20s -1 . The 1kHz pip rate was chosen based on previous publications for other odontocetes Popov et al, 2005;Nachtigall et al, 2007;Supin and Popov, 2007;Pacini et al, 2010) and a preestablished modulation rate transfer function of the experimental subject. The stimuli were digitally synthesised using a customised LabVIEW programme at an update rate of 512kHz, and the digitalto-analog conversion was accomplished by the NI USB-6251 BNC (National Instruments) data acquisition card connected to a laptop computer.…”

“…Since the first odontocete hearing was measured as a function of hearing threshold versus frequency of sound stimulus (i.e. an audiogram) in an Atlantic bottlenose dolphin, Tursiops truncatus (Johnson, 1967), audiograms of odontocete cetaceans have been measured using either psychophysical or evoked-potential methods in 16 species to date, including the harbour porpoise, Phocoena phocoena (Andersen, 1970;Kastelein et al, 2002), the killer whale, Orcinus orca (Hall and Johnson, 1972), the Amazon River dolphin, Inia geoffrensis (Jacobs and Hall, 1972), the beluga or white dolphin, Delphinapterus leucas (White et al, 1978), the Pacific bottlenose dolphin, Tursiops truncatus gilli (Ljungblad et al, 1982), the false killer whale, Pseudorca crassidens (Thomas et al, 1988), the Yangtze River dolphin, Lipotes vexillifer (Wang et al, 1992), Risso's dolphin, Grampus griseus , the common dolphin, Delphinus delphis (Popov and Klishin, 1998), the tucuxi, Sotalia fluviatilis guianensis (Sauerland and Dehnhardt, 1998), the Yangtze finless porpoise, Neophocaena phocaenoides asiaeorientalis (Popov et al, 2005), Gervais' beaked whale, Mesoplodon europeaus (Cook et al, 2006;Finneran et al, 2009), the white-beaked dolphin, Lagenorhynchus albirostris (Nachtigall et al, 2008), the long-finned pilot whale, Globicephala melas (Pacini et al, 2010), and Blainville's beaked whale, Mesoplodon densirostris (Pacini et al, 2011). However, as there are more than 70 species of odontocete cetaceans, those species for which nothing is known about their hearing sensitivity are still an overwhelming majority.…”

“…The AEP method has been widely used for audiometry in odontocete cetaceans. It has been successfully used for audiogram investigation of odontocetes in captive conditions (Popov et al, 2005;Pacini et al, 2010), catch-and-release scenarios (Nachtigall et al, 2008), and even in the wild for stranded animals (Mann et al, 2010).…”

Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas)

“…Most of what is known about odontocete hearing has come from individuals born or maintained in aquaria or laboratories for many years (Nachtigall et al, 2000). Few wild odontocetes have been studied and the ones that have were typically stranded due to healthrelated issues that could affect hearing (André et al, 2003;Finneran et al, 2009;Mann et al, 2010;Nachtigall et al, 2008;Pacini et al, 2010;Pacini et al, 2011). The auditory Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas) abilities of captive or stranded odontocetes may be robust as examples of species-specific hearing but the only way to test this assumption is to compare captive with wild, healthy animals.…”

Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

“…In particular, odontocetes (toothed whales, including porpoises and dolphins) have evolved highly developed high-frequency sound production systems and hearing capabilities for echolocation or biosonar (Nachtigall and Moore, 1988;Au, 1993). Odontocetes typically produce ultrasonic pulse signals (echolocation clicks) varying in frequency between 20 and 150kHz according to species (Au, 1993), and perceive signals with frequencies higher than (Au et al, 2000;Supin et al, 2001;Nachtigall et al, 2007) or, in a few species (Pacini et al, 2010;Pacini et al, 2011), close to 100kHz. Compared with most other mammals including humans, the auditory system of odontocetes is hypertrophied and characterised by a large volume of auditory nerve fibres, a high auditory ganglion cell count, and a high auditory innervation density in the inner ear (Ketten and Wartzok, 1990;Ketten, 1997).…”