Bioacoustics, aquatic soundscapes, monitoring 

On summer evenings in the 1980s, the residents of a houseboat community in Sausalito, California would often have trouble sleeping. A bizarre and persistent humming noise would keep them awake, and although they investigated, neither the residents nor the local authorities could pinpoint the problem.

They ruled out noise from generators, and even considered the possibility of secret military tests. It was researchers at the nearby Steinhart Aquarium who finally identified the culprit. The strange noise was the courtship song of male toadfish who were doing their best to attract females to their underwater love nests.

Back then, the field of bioacoustics – the scientific study of the production, transmission and perception of animal sounds – was a highly specialised and relatively remote research area. Underwater bioacoustics was even more niche, with only a handful of labs having access to the expensive equipment and technical know-how needed to record and decipher aquatic soundscapes.

Cheaper kits capable of more accurate recordings and powerful open source software have since brought the study of aquatic sounds to the scientific masses. This has led to a renaissance in our understanding of sound in the sea. And it turns out that the ocean is a very noisy place indeed... 

https://theconversation.com/listening-to-the-ocean-reveals-a-hidden-world-and-how-we-might-save-it-173790