Design and field test of a low-cost-portable linear array for marine mammal localization

Marine mammals are reliable bioindicators of aquatic systems health. Within this group, cetaceans are well known by their high dependence on sound for many of their vital activities such as: socialization and mating, prey catching and navigation. Due to its high dependence on sound, bioacoustic methods become very important in the study of these species. Acoustic monitoring in the field is usually performed using omnidirectional hydrophones to assess the presence of mammals, but for some behavioral studies it is also important to locate the animals, something which is not possible with that arrangement. Although there are very well known techniques to detect the Direction of Arrival of the sound, the equipment required is highly specialized and expensive. In this paper the design and field test of digital and analog versions of a portable linear array of hydrophones capable of locating animal sounds by beamforming, using low cost and easily available equipment is presented. The array was tested in La Paz bay, Mexico by experts of the Marine Mammals Research Program of the University of Baja California Sur which were able to locate dolphins (Tursiops truncatus) only by their sound, despite strong sources of noise in the area.