Since the mass of a whale is 200 tons on earth, and the moon has a lighter gravity compared to the earth is about 1/6 as powerful, the whale would weigh 33.33 tons with the last 3 repeating forever. so about 33 and one third ton on the moon.
This is talking about weight, which is how much it would take to lift this object, but the mass is the the same as mass isn't affected by gravity, only weight is affected by gravity.