Just an article about how Norwegian researchers are using fiberoptic cable without hydrophones to detect whales and earthquakes. Just sharing.
https://www.maritime-executive.com/editorials/existing-fiber-optic-cables-can-be-used-to-listen-for-whales

It's about time someone used time honored SIGINT methods to monitor acoustics and biologics. I worked research on this capability down in Texas in 1993 for other types of signals. A gigantic multi-static correlation and tracking network, that costs little, using existing deployed resources. 30yo technology, but highly effective.