https://www.scientificamerican.com/article/military-tries-out-fish-as-underwater-spies/

We humans often watch and wonder at wildlife. But a defense agency’s new initiative turns the tables—it aims to deploy marine animals to keep an eye on human activity.

The agency wants to know if sea life ranging from bioluminescent plankton to goliath grouper can serve as components of underwater surveillance systems capable of detecting the enemy’s oceangoing drones, large nuclear submarines and other underwater vehicles. The research effort is called Persistent Aquatic Living Sensors (PALS).