113.5 Saturday, Jan. 7 Hydrodynamic function of the cephalic lobes of the cownose ray for bottom swimming stabilization FISH, Frank E*; GABLER, Molly K; BENESKI, John T; MULVANY, Samantha; MOORED, Keith W; West Chester Univ., Pennsylvania; West Chester Univ., Pennsylvania; West Chester Univ., Pennsylvania; Univ. of South Florida, Tampa ; Princeton Univ. New Jersey firstname.lastname@example.org
The cownose ray (Rhinoptera bonasus) is an epipelagic swimmer that forages on the ocean bottom. To sense food under the bottom substrate, the ray deploys two depressible cephalic lobes, which are anterior modifications of the pectoral fins. The geometry and orientation of the cephalic lobes, when in contact with the bottom, indicate a potential passive hydrodynamic function. CT scans of cownose rays were used to define the external geometry of the animal with and without deployment of the cephalic lobes. Scale models of the rays without pectoral fins were produced with a 3D printer (ZPrinter 450) from reconstructed CT images. Models were tested in a flow tank at flow speeds in accordance with the typical swimming speeds of foraging rays. The models were connected to a force transducer to measure lift as the angle of attack was varied from -40o to 40o. A model head with the cephalic lobes deployed was constructed with dye injection ports for flow visualization. Models without cephalic lobes deployed generated a positive lift that increased curvilinearly with water speed. A negative lift was observed from models with the cephalic lobes extended. Flow visualization indicated that cephalic lobes directed the water flow downward in accordance with production of negative lift. Downward deflection of flow was due to a Venturi effect from the pressure difference between fluids located externally and internally of the lobes. The negative lift would aid in stabilizing the head to keep the sensory surface of the cephalic lobes in contact with the substrate and counter any pitching motions induced by oscillations of the pectoral fins.