New Scientist has an article on how scientists have designed a neural implant that could be used to control the brain signals of a shark. It could potentially be used to control the shark's movement and make the shark follow vessels without being "spotted." A whole new meaning to "stealth spies."
I could imagine using a school of sharks. Much like setting up a wireless sensor network. Except in this case, you utilize the shark's energy to power the movement of the "sensor nodes." One practical problem would be in getting hold of a number of sharks and implanting them. Furthermore, there might be ethical issues that would arise in the future once this technology gets on the radar of more people. Nonetheless, it seems like a fascinating use of techology. It remains to be seen how far Mother Nature will let mankind mess with her. Or will Hollywood beat them all to it with "The Return of Jaws - Underwater Spy."