Cetaceans are most identifiable with their forceful exhalation through the blowhole. The animal seemingly loses some bodily water through its blowhole during this fierce expiration, but the work of Coulombe et. al. reveals that the actual amount of water lost is miniscule. Coulombe looked at Atlantic bottlenose porpoises (Tursiops truncates) and Pacific white-sided porpoises (Lagenorhynchus obliqudens) to determine how much systemic water is lost from the respiratory tract. They found that 80% percent of the water in the respiratory tract was reclaimed before exhalation; meaning only 60 g of water per day would be lost from a 140 kg porpoise. This value is lower than nearly all terrestrial animals, including desert-dwelling animals (Coulombe et. al. 1965). The low ventilation-rate is primarily accountable for this fact, since terrestrial mammals inhale and exhale every few seconds while porpoises may take minutes between breaths. Porpoises and other cetaceans also control the pressure and cool the air in their respiratory passages to prevent water loss. By maintaining low pressures and temperatures in the respiratory tract, water vapor condenses and sticks to the tissue walls while only dry air is expelled from the lungs. Combined with low ventilation rates, these techniques help cetaceans to keep vital, systemic freshwater from evaporating into the air with each breath. The characteristic spout of water associated with cetacean respiration results because the animal begins to exhale before it breaks the ocean's surface.
The visible water from this whale's violent exhalation comes from the ocean, not its lungs. Photo provided by gimp-savvy.com.
