Meeting Abstract

P1.112  Saturday, Jan. 4 15:30  Fluid flow in filter feeding rays: Size XL PETERSON, A.N.*; PAIG-TRAN, E.W.M; SUMMERS, A.P.; University of Washington, Seattle; Arizona State University, Pheonix; Friday Harbor Labs, Friday Harbor

Mobulid fishes (mantas and devil rays) filter prey smaller than the pore size of their gill rakers. The filter array is formed from the five branchial arches. Each arch presents an anterior face directed at the incoming flow and a posterior face that is shielded from the incoming free stream. The flow through these filter elements is complex and varies with the angle and anatomy of the filter. We used four fold enlarged 3D physical models to examine fluid flow over a variation of filter morphologies and with different angles of attack. Models were based on the anatomy of Manta birostris filter lobes and created with a 3D rapid prototyper. This allowed us to vary the anatomy by removing projections and changing surface roughness. Fluid movement was investigated with a dye stream aimed to show flow in specific areas of the filter and the results were videotaped. In anterior and posterior orientations the fluid makes contact with the filter lobe and then makes a 90 degree turn into the filter pore. The vorticity of the system is complex and we distinguished three different processes that depend on orientation and fine scale morphology. First, there is vorticity parallel to the plane of the filter that moves downstream. There are also vortices parallel to the free stream and perpendicular to the filter plane continuously maintained in the pore opening. A third type of vorticity is seen in anterior facing filter lobes with projections, and consists of vortices shed downstream above the filter plane. This complicated vorticity indicates that some form of cyclonic filtration, a particle precipitation method that relies on circular flow, is playing an important role in the filter feeding of Mobulids.