Those animals are only members of the genus Balaenoptera furnished with dorsal fins, and like sperm whales, they're generally smaller than the bowhead whale.
One hypothesis states that bowheads might be singing so many songs because different populations are mixing together and bringing all their different songs to the mix.
Very early in their history, they managed to develop the technology to hunt the huge bowhead whale which was a staple food source for them at that time.