In the framework of the OHASISBIO observatory: hydroacoustic monitoring of the low-level seismicity associated with the Indian seafloor spreading ridges, and of the presence and migration patterns of large baleen whales in the southern Indian Ocean, a hydrophone prototype has been deployed by 24°S 63°E. This prototype has an autonomy of 3 years and the data can be retrieved with messengers, releasable on demand. This instrument complements the observatory now composed of 9 distant moorings equipped with autonomous hydrophones. For the first six months (test phase), it will acquire data in parallel with an autonomous hydrophone (MAD-E) installed nearby in January 2018 (MD211 cruise).