Does rotation increase the acoustic field of view? Comparative models based on CT data of a live dolphin versus a dead dolphin

Abstract

Rotational behaviour has been observed when dolphins track or detect targets, however, its role in echolocation is unknown. We used computed tomography (CT) data of one live and one recently deceased bottlenose dolphin together with measurements of the acoustic properties of head tissues to perform acoustic property reconstruction. The anatomical configuration and acoustic properties of the main forehead structures between the live and deceased dolphins were compared. Finite element analysis (FEA) was applied to simulate the generation and propagation of echolocation clicks, to compute their waveforms and spectra in both near- and far-fields, and to derive echolocation beam patterns. Modelling results from both the live and deceased dolphins were in good agreement with click recordings from other, live, echolocating individuals. FEA was also used to estimate the acoustic scene experienced by a dolphin rotating 180° about its longitudinal axis to detect fish in the far-field at elevation angles of -20° to 20°. The results suggest that the rotational behaviour provides a wider insonification area and a wider receiving area. Thus, it may provide compensation for the dolphin’s relatively narrow biosonar beam, asymmetries in sound reception, and constraints on the pointing direction that are limited by head movement. The results also have implications for examining the accuracy of FEA in acoustic simulations using recently deceased specimens.

Spin-leap performance by cetaceans is influenced by moment of inertia

“…Particularly, marine mammals (cetaceans, pinnipeds, sirenians) will roll the body to turn by banking in order to facilitate use of their lateral control surfaces to hydrodynamically generate a centripetal force ( Fish and Battle, 1995 ; Fish, 2002 ; Fish et al, 2003 ; Cheneval et al, 2007 ; Wiley et al, 2011 ; Segre et al, 2018 ; 2022 ). Underwater rolling is used by dolphins to increase the echolocatory insonification to the receiving areas to compensate for the asymmetrical and narrow echolocation beam ( Wei et al, 2023 ). Rolling can also be used by the animal to change its energy state and linearly decelerate by transferring linear kinetic energy for translational speed to rotational kinetic energy as in the case of banked aerial turns ( Giancoli, 1991 ; Lissaman, 2007 ).…”