Meeting Abstract
Balaenid whales feed on large aggregates of small and slow-moving prey (predominantly copepods) through a filtration process enabled by baleen. These whales exhibit continuous filtration, namely, with the mouth kept partially opened and the baleen exposed to oncoming prey-laden waters while fluking. This filtration process is an example of crossflow filtration (CFF) in which most of the particulates (prey) are separated from the substrate (water) without ever coming into contact with the filtering surface (baleen). This poster will present the results of baleen filtration hydrodynamic simulations based on a type of hydraulic circuit modeling commonly used in microfluidics, but adapted to the much higher Reynolds number flows typical of whale hydrodynamics. This model uses as input the basic characteristics of the flows moving through a section of baleen observed in a previous flume study by the authors. Although of low-spatial resolution, the model fully incorporates the effects of fluid viscosity which, through the boundary layer enveloping the surface of each baleen, generates enough friction to at least double a whale’s total body drag in comparison to non-feeding travel. Modeling viscous friction is crucial here since exposing the baleen system to the open ocean ends up tripling a whale’s total wetted surface area. Among other findings, the model shows how CFF is enhanced by a large filtration surface and hence large body size; how it is carried out via the establishment of rapid anteroposterior flows transporting most of the prey-water slurry towards the oropharyngeal wall, along with substantially slower intra-baleen flows that transfer most of the substrate out of the mouth; and the general decrease in overall speed of both flows as they approach the oropharyngeal wall.
