Both marine mammals and hydroacoustic instruments use underwater sound to communicate, navigate and/or infer information about the marine environment. Concurrent timing of acoustic activity and/or the use of similar frequency regimes will thereby result in (potentially mutual) masking of acoustic signals. Earlier studies have provided evidence that masking by anthropogenic sound sources might negatively impact marine mammal population health. Hydroacoustic studies on the other hand may generate low quality data or suffer data loss as a result of interference from biological acoustic sources. This study provides an overview of the vocal characteristics of Arctic and Antarctic marine mammals, showing that each species has its own specific acoustic niche with surprisingly little frequency and/or temporal interspecific overlap. The acoustic characteristics of marine mammal vocalizations are compared with the characteristics of common hydroacoustic instrumentation, such as airguns, naval and fishery sonars, sediment and fan-beam echosounders as well as tomographic and RAFOS sources to identify overlaps and ‘open’ acoustic spaces, i.e. frequency bands and periods of low marine mammal acoustic activity. Using this information to separate biotic and anthropogenic sound is expected to contribute to a reduction of contingent adverse effects of anthropogenic sound sources on breeding, foraging and migration success of marine mammals, while at the same improving data quality of hydroacoustic studies. Nevertheless, we also caution that limiting the amount of anthropogenic sound introduced to the ocean still is paramount to a healthy acoustic ecology.