Here's some info from a few years ago. Can you imagine fishing for a cable 9,400 meters underwater?
Alcatel breaks world record in deep-sea cable repairs - Undersea
Fiber Optics Weekly Update, June 27, 2003
Alcatel has successfully completed a fiber optic cable repair in water depths close to 9,400 meters -- breaking the world record for deep-sea cable repair operations. The Alcatel operated cable ship, C.S. Heimdal, completed the fiber optic cable repair approximately 700 km off the coast of Japan on a transpacific cable system connecting Japan to the U.S. continent. Because of the extreme water depths involved, Alcatel created a special grapnel to avoid the cable breaking under its own weight as the cable was raised from the seabed for repair. Based in Japan and fully mobilized with remotely operated vehicles, the C.S. Heimdal vessel enables Alcatel to help its customers respond to potential cable outages within 12 hours.
Appreciated.