Most military underwater surveillance systems filter out whale calls along with other ambient ocean noise. This inspired researchers from China's Tianjin University to create a form of "bio-inspired steganography" in which recordings of whale songs can be edited to contain secret messages and then electronically transmitted underwater. From Newsweek:
In research published in IEEE Communication Magazine, the team said there are two ways to hide signals in whale pulses—changing the signal to include encrypted information or making the signal weaker.
The former is problematic because it would stand out from other naturally occurring signals, Jiang told SCMP. However, the second method holds promise. Researchers could build a coding system around the whale sounds. They could then edit whale sounds so they are indistinguishable from other whale calls. When they are received by the coding system, they can be deciphered. The main drawback for this approach is that it would be difficult to send a message over a long distance.
"Bio-Inspired Steganography for Secure Underwater Acoustic Communications" (IEEE Communications)
Image: "A mother sperm whale and her calf off the coast of Mauritius" by Gabriel Barathieu