Yes, "blue whale" should be capitalized when it is part of a formal name, such as in scientific literature or when referring to the species as "Balaenoptera musculus." However, in general writing, it is typically written in lowercase unless it starts a sentence. Always consider the context in which the term is used.
blue whale about
The blue whale. It is the biggest animal on Earth.
blue whale
Blue WhaleBalaenoptera musculus is the scientific name for a blue whale!
Balaenoptera musculus is the biological name for the blue whale.Blue whale, or baleen whale.
The Blue Whale is the largest animal living on Earth.
a blue whale
Balaenoptera musculus is the scientific name of Blue Whale
No more than you'd capitalize 'human'.
No it's blue the clue is in the name.
philbert
A whale or a blue whale