The present invention is directed to acoustics and signal processing. More specifically, the present invention is directed to a system and methods by which whether and the time during which one or more subjects are present within a given area of a marine or terrestrial ecosystem, and other information regarding the subjects can be efficiently determined by the sounds that the subjects produce. Advantageously, certain embodiments of the present invention permit a user to select and rapidly produce one or more visual presentations of the signals of interest (SOI) recorded from the passive acoustic monitoring of a given area of an ecosystem in order to obtain additional information about the subjects.