Audiometric procedures in yearling southern elephant seals of Marion Island

• Main Authors: Bornemann, Horst, Kindermann, Lars, Plötz, Joachim, Bester, M. N.
• Format: Conference Object
• Language: unknown
• Published: 2007
• Subjects: Antarctic; Antarc*; Elephant Seal; Elephant Seals; Marion Island; Southern Elephant Seal; Southern Elephant Seals
• Online Access: https://epic.awi.de/id/eprint/18054/; https://epic.awi.de/id/eprint/18054/1/Bor2007d.pdf; https://hdl.handle.net/10013/epic.28595; https://hdl.handle.net/10013/epic.28595.d001

The audible frequency ranges and corresponding hearing thresholds are the most characteristic properties of any auditory system. They are typically displayed in the form of an audiogram as the function of minimal audible sound level in respect to frequency. For about 90% of marine mammal species including all Antarctic seals audiograms have not been measured as yet, and knowledge about their hearing is limited to assumptions based on measurements on similar species and frequency ranges of their own vocalisations, with the underlying assumption that vocalisation frequencies correspond with hearing abilities. However, it is well known that hearing is possible in excess of up to several octaves beyond the vocalisation frequencies since hearing has not only evolved as a function of communication; and marine mammals in particular have evolved to use sound and hearing as their primary means of perceiving their surroundings. Recordings of vocalisations related to reproductive or feeding behaviour as well as measurements of hearing abilities are therefore very relevant to interpret population ecology as well as several other aspects of seal biology.We used electro-encephalography to measure auditory evoked potentials, especially the auditory brainstem responses of immobilised southern elephant seal yearlings. The field study was conducted at the haulout sites of elephant seals close to the Marion Island Research Base (46°54S, 37°45E) from 12 to 24 April 2007. Five 1.5 years old seals were chosen for experiments. We developed a portable experimental set-up in order to test for basic audiogram data. The experiment was focussed on a mapping procedure to identify areas on the seals head most suitable for AEP recordings by seeking for optimal electrode placements, where signal to noise ratios are best. The poster shows the methodological approach, presents first results on audiometric procedures on southern elephant seals, and discusses the ecological relevance of audiometric investigations.