I want to mention Ivano Pelicella of Dodotronics who has helped develop this project in secret over the last few months by supplying components etc. such as the Nvidia Jetson Nano. Ivano is a specialist microphone developer in Italy and the project currently uses his Ultramic-384k-ble USB mic. Obviously, to monitor aquatic mammals, a waterproof mic is required and Ivano is developing this very thing, literally, as we speak. Here are the moulds for the prototype:

Hydrophones are extremely hard to find / expensive, but essential to this project for the future.