Click and tone-pip auditory evoked potentials in a large marine mammal, the northern elephant seal

Abstract

The use of auditory-evoked potentials (AEPs) to study the hearing of mysticete whales is challenged by access to animals, their large size, and proportionately smaller brain relative to odontocetes. One means by which AEP techniques can be adapted to these larger animals is by application to more readily available proxy species. The northern elephant seal (Mirounga angustirostris) is a large pinniped, potentially in excess of 2000 kg, with a thick dermis, large skull, relatively small auditory nerve, and a low-frequency vocal communication system. AEP collection in elephant seals provides similar challenges to those of the mysticetes but at a scale that provides a greater opportunity for success. AEP tests were conducted on northern elephant seals at Año Nuevo State Reserve, the natural haul-out site of the elephant seal. Subjects were chemically immobilized with tiletamine/zolazepam and chemical restraint was maintained with bolus injections of ketamine. Click-evoked potentials were collected from four weanling and two adult male elephant seals and tone-pip-evoked potentials were collected from a 2-year-old female. Results demonstrate that AEPs can be recorded from large pinniped species, providing a step towards the application of similar techniques to larger cetacean species.