Most marine mammals, such as sperm whales and long-finned pilot whales, always produce call pulses with certain characteristics for echolocation, communication, and so on. Generally, the enemy's underwater reconnaissance system almost always classifies these biological signals as ocean noise and then filters them out. Based on this fact, this article provides our attempts at a novel steganography to conceal digital communications in the constructed communication frame composed of original marine mammal call pulses. We first put forward a screening scheme to pick out high-quality call pulses from the original marine mammal call pulses. Next, we discuss how to design a secure, camouflaged, and covert communication frame according to the characteristics of marine mammal call pulses. Both the time delay difference among communication codes and the number of communication codes are simultaneously used to convey the digital information. The ambiguity function and correlation technique are utilized to select communication codes from original whale call pulses. In the end, experiments were performed to demonstrate the validity and security of the bio-inspired steganography. The presented bio-inspired steganography is able to serve a variety of underwater military communications, such as submarine communications and autonomous underwater vehicle communications.