One of the major risks of deep-diving for any animal is decompression sickness. Most common in SCUBA divers, this condition occurs when gaseous nitrogen in the lungs is pushed into the bloodstream because of the immense force of the water pressure. Normally, this gas is exhaled as the diver slowly ascends, but if the ascension is too fast the gas will not be exhaled and will collect in the joints and respiratory tissues (Marshall 2002). Decompression sickness causes pain and death in humans if left untreated. Cetaceans and other deep-diving marine mammals are immune to ‘the bends’ because of beneficial anatomical traits.
The respiratory tract directly inside this whale's blowhole will resist compression, allowing vascular gases to stay out of the peripheral tissues during deep dives. Photo provided by gimp-savvy.com
Two vital adaptations of the respiratory system allow cetaceans to safely traverse the ocean’s depths. Thick cartilaginous rings surround the conduction tract which leads from the blowhole to the lungs. These rings maintain the shape of the respiratory tract even against the great pressure of the deep ocean and ensure that no gases diffuse into the peripheral tissues. Cetacean lungs are very resilient and can readily re-inflate once they have collapsed, unlike human lungs. So at great depths when the chest cavities of whales, dolphins and porpoises are subject to great pressure, their lungs collapse and all of the air is forced into the reinforced conduction tract (Marshall 2002). Since the cartilage will not compress, the air from the lungs is stored in this open space until the animal ascends and the gas re-expands and refills the lungs and alveoli.
Species |
Max. Time |
Max. Dive Depth |
Pacific white-sided dolphin |
5 (minutes) |
210 (meters) |
Bottlenose dolphin |
10 |
535 |
Killer whale |
15 |
250 |
Narwal |
20 |
1000 |
Humpback whale |
20 |
150 |
Gray whale |
25 |
170 |
Fin whale |
30 |
500 |
Blue whale |
50 |
100 |
Bowhead whale |
80 |
300 |
Bottlenose whale |
120 |
1000 |
Sperm whale |
140 |
3000 |
Table shows the extreme diving depths of some cetaceans. Decompression sickness can occur in humans if they ascend too quickly from 10 meters below the surface, while the Sperm whale (Physeter macrocephalus) can avoid the same ailment after diving 300 times deeper. Figure adapted from ACS 2005.
