Complex sentence: However, it has a surprisingly low density, weighing only a mere 878 lbs. (which may be a reference to characteristics it attains from a zeppelin), whereas the similarly girthed humpback whale weighs from 30 to 50 tons.
Split into simpler sentences: However, it has a surprisingly low density, weighing only a mere 878 lbs, in accordance with its appearance characteristic of a zepphelin. The similarly girthed humpback whale weighs from 30 to 50 tons.