Scientists have found hybrids or crosses, indicating that blue whales and fin whales sometimes mate with one another. They make a low-frequency sound that sounds very deep, like a moan. These sounds are probably used for communication. In addition to communication, the moans may aid in navigation by serving as a form of long-distance echolocation for oceanographic features. Blue whales often have remoras attached to them.
Remoras are small fish that are 'hitchhikers'.
We don't know how long blue whales live, but certainly more than 50 years for both males and females. Individual blue whales may be identified by the mottling or blue marbling pattern of the sides of their bodies, as well as notches or shapes in the dorsal fin. There are three subspecies of blue whale. Best of luck with your report, and write back if you have more questions.