Meeting Abstract
Mobulid fishes are large filter-feeding elasmobranchs that capture zooplankton using a filtering apparatus formed from highly modified gill rakers. Many filter-feeding animals capture prey using sieve filters, in which water is forced through an array of pores and any particles smaller than the pore size are trapped. However, previous studies using physical models have indicated that the filtering apparatus of mobulid fishes operates via a different mechanism. Water flowing over the apparatus appears to produce a train of captive vortices that repel zooplankton away from the filtering apparatus and concentrates them within the buccal cavity. However, the hydrodynamic forces that give rise to this filtering effect are still not well understood. In this study, we constructed a computational fluid dynamics model of the filtering apparatus and calculated the flow velocities around the filter. We then simulated the trajectory of solid particles traveling through the calculated flow field using equations of motion that include inertia, added mass, drag, contact forces, and shear-induced lift. These simulations predict that captive vortices can function as filters, and this model provides new insights into the hydrodynamic forces that produce this effect.
