In recent years, oceanic based research is gradually growing across the globe. Most researchers in this field aim at resolving the major challenges of Underwater Acoustic Sensor Networks like limited bandwidth, high propagation delay, 3D topology, media access control, routing, resource utilization, and power constraint neglecting spectrum utilization. However, most UAN designs consider the acoustic communication in underwater as a single network and only a very few consider the existence of other multiple acoustic systems in the ocean. Both the natural acoustic systems and artificial acoustic systems in the ocean use the acoustic means of communication leading to a heavily overcrowded spectrum. Despite the oversharing of channels the spectrum is still temporally and spatially underutilized. Unlike cognitive radio, spectrum allocation in cognitive acoustics is highly challenging due to the unique features of the underwater channel and the acoustic systems. The increasing intervention of anthropogenic activities in the oceans has resulted in an overshared, scarce, and inefficiently utilized spectrum. As an effort to calm down these adverse impacts, an underwater cognitive acoustic network-based spectrum decision strategy is proposed in this paper to aid in efficient spectrum utilization and allocation by multiple acoustic systems in the underwater environment. The proposed strategy is aimed at an environmentally friendly spectrum utilization model with much emphasis given to the primary users, the marine species. This paper considers all possible marine species and not just limit it to marine mammals. Finally, the scope of this paper is to provide an in-depth view of cognitive acoustics in UASN that can pay way for environmentally safe underwater research and marine habitat conservation in the future. © 2020 Elsevier Ltd