Flow-induced aggregation of zooplankton requires at least two elements: a nonuniform flow field and a biological behavior pattern that governs the swimming of the organisms. Completely passive tracers cannot aggregate because the water parcels that they follow cannot aggregate (there being no internal sources or sinks of water). Completely random swimming also would not lead to quasi-steady aggregation. The flow fields around oceanic fronts are intrinsically nonuniform. One primary characteristic of surface fronts is a convergence in the surface flow. A behavioral pattern that partially removes organisms from the constraints of such a flow field, and that can lead to bioaggregation, is depth-keeping. This talk examines ways in which depth-keeping organisms can be aggregated or concentrated by flow fields characteristic of physical fronts. Both moving and stationary fronts are considered.