Abstract: Results of theoretical and experimental investigation on marine mammal acoustics are presented and briefly concluded. The described research is a part of interdisciplinary scientific project titled „Bionic Sonar”. The goal of the project is to develop a new kind of hydroacoustic sources with specified frequency characteristics and directivity patterns, inspired by the vocal and echolocation systems of the marine mammals. The presented theoretical investigation focuses on underwater communication and navigation capabilities of dolphins and grey seals. The experimental research concerning underwater vocalizations of the grey seals was performed in the Hel Marine Station of the Institute of Oceanography of the University of Gdańsk. Underwater sounds were recorded using hydrophones placed in the pools in which only the grey seals were present. The recorded vocalizations have been extracted from the recordings and analyzed for a number of distinguishing characteristics. The obtained results are compared to the results of other related investigations described in literature.