NAUWELAERTS, S*; WILGA, C.D.; SANFORD, C.P.; LAUDER, G.V.; University of Rhode Island; University of Rhode Island; Hofstra University; Harvard University: Substrate Increases Suction Feeding Effectiveness In Bamboo Sharks
The effectiveness of suction feeding depends on the fluid flow pattern around the mouth and modulation of prey capture. Prior modeling and empirical findings have shown that significant fluid velocities are confined to a region within one mouth width (MW) from the mouth. Therefore the predator must be relatively close to the prey to ensure successful capture using suction. Most of those studies were conducted on bony fishes that feed in the water column. Bamboo sharks, Chiloscyllium plagiosum, live in benthic environments and are suction feeding specialists. They typically feed on the substrate, but they occasionally take prey from the water column as well. We predict that, due to conservation of momentum, the velocity field will change shape by decreasing in height and therefore increasing in width and length when feeding on the substrate. This will cause the boundary of the fluid field to lie further away from the mouth, thereby exceeding the theoretical prediction of a maximal one MW distant flow field. To test these predictions, we used high resolution DPIV to analyze the hydrodynamics of feeding from the substrate and water column. A vertical laser sheet was used to illuminate particles and visualize the fluid field. Bamboo sharks were fed squid at various heights from bottom. DPIV analysis showed that the boundary of the flow field can be increased up to 2.5 MW distances due to a passive substrate effect. This indicates that the substrate extends the distance that suction is effective and requires less accuracy than feeding in the water column using the same suction effort. The region of greatest fluid velocity was located slightly anterior to the mouth opening, indicating the presence of a bow wave. Such a wave is the consequence of equilibrium between backwards momentum of water flowing into the mouth and forward movement of the fish itself.
