Page 77 - Spring 2018

Obituary | Bertel Møhl | 1936-2017
Bertel Møhl, Fellow of the Acoustical Society of America (ASA), passed away in his home in Dyssekilde, Denmark. Bertel was a pioneer in bioacoustics and paved the way for others to continue in his footsteps.
Bertel grew up not far from Co-
penhagen. After completing his studies in zoology at the University of Copenhagen, he was the first to measure the hearing sensitivity of seals in air and underwater. Together with Søren Andersen, Bertel also de- scribed the high-frequency component of harbor porpoise clicks. He was tenured at Aarhus University, Aarhus, Den-
mark, in 1969.
Bertel then extended his work on hearing to other animal groups. He discovered ultrasound production in butterflies as a countermeasure to echolocating bats. He refuted the idea of a coherent receiver in bat biosonar through an el- egant psychophysical experiment. With colleagues from the University of Hawai’i, Honolulu, he showed unequivocally that the lower jaw of dolphins acts as a sound receiver.
In the 1970s, Bertel visited whaling stations in Spain and Ice- land to study the anatomy of sperm whales. How could an animal with such a huge nose catch fast-moving squid under water? Together with Kenneth Norris, Bertel formulated the “big bang hypothesis,” suggesting that toothed whales may stun their prey with loud sound pulses produced in the nose.
Through a long series of field studies, Bertel showed that both narwhals and sperm whales produce extremely intense biosonar signals. To determine source levels, he developed a novel acoustic localization system using GPS-linked re- ceiver units. He also constructed a deep-sea hydrophone unit, operating at 500 m depth, by using the coated wire as the electric signal path and the seawater as the return path. Data from acoustic tags have subsequently refuted the idea of acoustic debilitation by sperm whales. Still, Bertel’s inge- nious field studies continue to be relevant and inspire many marine mammologists.
Bertel’spassionfortechnicalinnovationsdidnotceasewith age. After he turned 70, he developed a fiber-optic-linked deepwater linear hydrophone array. It went onboard his 45- foot steel ketch r/v Narhvalen to East Greenland, Northern Norway, and the Canary Islands and could record whales down to depths of 1 km. He also collaborated with Mark Johnson and his former student Peter Madsen, and during a final field study in the Azores, they combined deep-sea linear hydrophone arrays with acoustic tags to obtain detailed in- formation on the acoustic foraging behavior of sperm whales. After the Azorean expedition, he and his wife Lotte, who had accompanied him on several expeditions, stayed on land.
Bertel Møhl has left a legacy of innovative and outstanding research that continues to be an important source of inspira- tion. He is missed not only by family and friends but also by former students and colleagues all over the world.
Selected Articles by Bertel Møhl
Møhl, B. (1968). Auditory sensitivity of the common seal in air and water. The Journal of Auditory Research 8, 27-38.
Møhl, B. (1986). Detection by a pipistrelle bat of normal and reversed rep- lica of its sonar pulses. Acustica 61(1), 75-82.
Møhl, B., Au, W. W. L., Pawloski, J., and Nacthigall, P. E. (1999). Dolphin hearing: Relative sensitivity as a function of point of application of a con- tact sound source in the jaw and head region. The Journal of the Acoustical Society of America 105(6), 3421-3424.
Møhl, B., Wahlberg, M., and Heerfordt, A. (2001). A large-aperture array of nonlinked receivers for acoustic positioning of biological sound sources. The Journal of the Acoustical Society of America 109(1), 434-437.
Møhl, B., Wahlberg, M., Madsen, P. T., Heerfordt, A., and Lund, A. (2003). The monopulsed nature of sperm whale clicks. The Journal of the Acoustical Society of America 114(2), 1143-1154.
Norris, K., and Møhl, B. (1983). Can odontocetes debilitate prey with sound? American Naturalist 122, 85-104.
Written by:
Magnus Wahlberg, Email: magnus@biology.sdu.dk
Marine Biological Research Center
University of Southern Denmark, Kerteminde Whitlow Au, Email: wau@hawaii.edu
Hawai’i Institute of Marine Biology University of Hawai’i, Kane’ohe
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