Fluid Mechanics of Suction and Ram Feeding in Elasmobranchs.

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FLUID MECHANICS OF SUCTION AND RAM FEEDING IN ELASMOBRANCHSCheryl A.D. Wilga, University of Rhode IslandThe overall goal of this research is to quantify the pattern of water flow around and into the mouths of suction and ram feeding sharks and skates, and to describe the mechanism by which it was generated. Suction flow into the mouth of a shark is generated by rapid expansion of the mouth and gill cavities, which pulls the prey into the mouth. In contrast, ram feeders simply open their mouths wide and engulf their prey with relatively little expansion. Three species based on the type of feeding morphology and mechanism exhibited will be investigated in this study: bamboo sharks, Chiloscyllium plagiosum, are specialized for suction feeding; little skates, Raja erinacea, are also specialized for suction feeding; and swellsharks, Cephaloscyllium ventriosum, are specialized ram feeders. Using these species, previous hypotheses about the anatomy of ram and suction feeding fishes and the mechanism of suction generation will be tested.The specific aims of this research are to: quantify the anatomical characteristics of the muscular and skeletal elements of the ram and suction feeding sharks and a suction feeding skate; construct biomechanical models that involve the force and speed of ram and suction feeding, and output of various muscular and skeletal elements; quantify cranial and gill movements during feeding using sonomicrometry; quantify activity patterns of cranial muscles thought to be involved in the generation of suction using electromyography and video; and visualize and quantify the patterns of water flow generated by suction and ram feeding using digital particle image velocimetry (DPIV). The integrative approach in combining these techniques will allow a fuller understanding of the relationship between anatomy, feeding mechanism, muscular effort, suction generation, and water flow.These objectives include two techniques that have yet to be applied to studies of shark feeding: sonomicrometry and DPIV. A major advantage of quantifying movements using sonomicrometry over video is that continuous quantification of moving structures are recorded even though structures may not be visible externally or have moved out of camera view. The relatively new technique of DPIV will provide direct visualization and quantification of the development of water flow around and into the head of feeding sharks and skates throughout the feeding event. This has been the goal of many researchers interested in the feeding mechanism of aquatic vertebrates, but has been hampered by the lack of accurate quantifiable images of the fluid moved by the feeder, now available with DPIV. This project is significant in that it will improve our understanding of the internal muscular and kinematic events that generate suction and their relationship to fluid flow. This study will demonstrate the usefulness of DPIV and sonomicrometry for studies of other aquatic feeding vertebrates. In addition, the proposed research will increase our knowledge of feeding mechanisms in vertebrates, and elasmobranchs in particular, by evaluating the role of anatomy in function. Finally, the proposed research will contribute to our understanding of feeding behavior and the evolution of vertebrate musculoskeletal mechanisms. This research will provide a basis for interpreting the evolution of key musculoskeletal systems in the most basal of gnathostomes: most agree that skates have evolved from sharks. This study on the most ancestral of all living jawed vertebrates will provide the basis for further studies on the flow mechanics of aquatic feeding in more derived vertebrates, such as bony fishes and salamanders.