Title Bioacoustics, Innovation, and Ecomorphology in Marine Vertebrates

By some estimates, the level of low‐frequency anthropogenic noise in the world's oceans has doubled every decade for the past 5 decades. Current oceanic noise levels can produce deleterious impacts on marine organisms and their ecosystem. Our research focuses upon the functional morphology of bioacoustic mechanisms and sensory biology in whales and other large marine vertebrates. The aquatic existence of cetaceans often puts them beyond our reach, but it is primarily the size of the large whales that makes them intractable subjects of investigation. A revolution in anatomy and physiology has been catalyzed by remote imaging technology over the past few decades. The development of industrial size x‐ray computed tomography (CT) scanners make it possible to collect information about the intact anatomy of large whales. The serial 2‐D CT scan data can be reassembled into volumetric models that can provide unique morphological visualization and the foundation for finite element analysis. Over the past ten years, we have developed a vibroacoustic toolkit by combining CT scan data with finite element modeling (FEM) techniques. This innovative computational approach allows us to visualize the biomechanical interactions between underwater sounds and the complex anatomic geometry of aquatic organisms. We have uncovered and untangled intricacies of baleen whale hearing pathways, along with biosonar signal generation and beam formation in toothed whales. Vibroacoustic modeling requires high‐resolution anatomic geometry as input. This required us to develop techniques to CT scan animals of all sizes, from small fish and medium size pinnipeds or dolphins, and recently an entire baleen whale. An industrial CT scanner, designed for solid‐fuel rocket motors, was used to extract the anatomic geometry from an entire minke whale. Our computational FEM methods allowed us to discover the that the primary mechanism of low‐frequency (LF) sound reception in baleen whales is bone conduction, primarily through the skull. We also derived the first synthetic audiogram for a fin whale (Cranford and Krysl, 2015). Our current hypothesis is that all cetacean heads function like sound reception antennas. Input to the ears are the integration (summation) of the inputs from the entire surface of the head. Some areas on the head contribute more than others, but there is no single or bilateral channel or “window”. The head processes various acoustic inputs according to frequency, amplitude, and incident trajectory. Different input pathways can coalesce or interfere with one another constructively or destructively, according to a complex set of rules. These complex interactions between pathways apparently vary with species specific anatomic geometry. Since oceanic anthropogenic noise is largely LF in nature, understanding how various marine vertebrates receive, process, and mitigate the effects LF sound is crucial for assessing the potential impacts of chronic or acute exposure. Support or Funding Information We appreciate and acknowledge support from: Michael Weise and Dana Belden (Office of Naval Research); Frank Stone, Ernie Young, Robert Gisiner, and Danielle Buonantony (Chief of Naval Operations CNO45); Anurag Kumar and Mandy Shoemaker (Living Marine Resources NAVFAC EXWC); Curtis Collins and John Joseph (Naval Postgraduate School); Judy St. Leger (SeaWorld San Diego); Charley Potter (Smithsonian Institution); John Hildebrand and Sean Wiggins (Scripps Institution of Oceanography); Staff at Missile X‐ray Facility (Hill Air Force Base); Jim Christmann and Dave Jablonski; Michael Philcock (Analyze Direct).Skin and skeleton of an entire minke whale ( Balaenoptera acutorostrata ) from CT scans.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .