As Melville pointed out , if a sperm whale can spend more than an hour swimming at depths of up to 6,000 feet , and a sperm whale is composed mostly of gas ( air-filled lungs and blubber ) , then Boyle 's law would dictate that , as Spruch puts it , a whale of regulation size at the surface should , at the pressures a thousand fathoms down , decrease its volume to the size of a bathtub !
A sperm whale can only go to 2,000 feet .