Collective motion is a widespread phenomenon observed in nature at multiple scales: from bacteria to humans. In the ocean, small organisms (like krill) swarm and migrate up-and-down the water column in order to avoid large predators. Our research focuses on studying the hydrodynamics associated with this behavioral trait at scales where both viscous and inertial effects are important. Using experimental velocimetry techniques (PIV), we quantify fluid transport and induced mixing due to a migration event to estimate the contribution of organisms in sustaining their own ecosystem.