Final answer:
Scientists utilize DNA analysis and examination of physical traits to determine whether a whale like Blue 55 is a hybrid. While Blue 55 isn't a recognized specific hybrid, this is the method researchers use to identify hybrid cetaceans.
Step-by-step explanation:
Scientists were able to determine that Blue 55 was a hybrid whale through a combination of genetic analysis and observation of physical characteristics. In the case of cetaceans like the Australian humpback dolphin, Sousa sahulensis, scientists used coloration, skeletal structure, habitat, and DNA to confirm that it was a separate species. Similar methods are employed to identify hybrids in the wild, where analyzing the DNA can reveal the ancestry of the species and confirm if it's a hybrid of two different species.
It's important to note that while the question mentions 'Blue 55', as per available knowledge, there is no specific hybrid whale universally known by that name. The methodology mentioned above, however, is a standard approach to identifying hybrid species in marine animals, which includes combinations such as those between different species of orca whales as described in provided information.