Detection and tracking of chemical trails by local sensory systems

Many aquatic organisms exhibit remarkable abilities to detect and track chemical signals when foraging, mating and escaping. For example, the male copepod { \em T. longicornis} identifies the female in the open ocean by following its chemically-flavored trail. Here, we develop a mathematical framework in which a local sensory system is able to detect the local concentration field and adjust its orientation accordingly. We show that this system is able to detect and track chemical trails without knowing the trail's global or relative position.