Abstract: A method and system of deterring mammals is disclosed involving incurring an acoustic startle response comprising the steps of selecting a target order, family, genus or species to be deterred, selecting a received level that is a predetermined level above a representative hearing threshold of the targeted mammals, and, taking transmission loss into account, transmitting an acoustic signal at a source level required to create the selected received level at a predetermined distance from the transmission point. The acoustic signal may comprise frequency components at which the aural sensitivity of the targeted mammals is greater than that of selected other animals, preventing the disturbance of the selected other animals whilst deterring the targeted mammals. In addition, a secondary conditioning sound may be played prior to the main acoustic signal to condition the mammals to avoid the main stimulus.