In summary, the primary anatomical adaptations for pressure of a deep-diving mammal such as the sperm whale center on air-containing spaces and the prevention of tissue barotrauma. Air cavities, when present, are lined with venous plexuses, which are thought to fill at depth, obliterate the air space, and prevent "the squeeze." The lungs collapse, which prevents lung rupture and (important with regard to physiology) blocks gas exchange in the lung. Lack of nitrogen absorption at depth prevents the development of nitrogen narcosis and decompression sickness. In addition, because the lungs do not serve as a source of oxygen at depth, deep divers rely on enhanced oxygen stores in their blood and muscle.
Article originally published on May 2, 2002.
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Add CommentI understand that free divers (those not breathing compressed air from scuba tanks) don't get the bends. Apparently that's because no new air is added to the lungs during the dive, preventing super-saturation of the blood. I guess the air that was pressed out of their lungs into their blood just goes back into their lungs as they surface (rather than into nerve tissue/joints, etc). So, it seems like seals wouldn't get the bends either, even if they did not collapse the lungs. What am I missing? Thanks. (Could lung collapse also be a way to reduce bouyancy for the dive?)
Reply | Report Abuse | Link to thisThe answer to the centuries-old mystery of why whales beach themselves can stated in only one word:
Reply | Report Abuse | Link to thisBAROSINUSITIS
Barosinusitis in diving sea mammals is a pressure-related injury in the sinuses and air sacs located inside their heads.
It is well-known that rapid and excessive changes in the surrounding water pressure can cause physical trauma in all diving mammals, including man.
Severe oscillations in pressure (seaquakes) are common above the epicenter of certain shallow-focused undersea earthquakes, especially those located in the rift valley of mid-ocean ridges.
Navy sonar, oil industry airguns, and underwater explosives cause the same barosinusitis injury as caused by undersea earthquakes.
In toothed whales, the sinuses and air sacs serve as acoustic mirrors reflecting sound inside their heads in such a fashion to enable their echo-navigation system to function properly. An injury in this critical part of their biosonar system naturally disrupts echo-navigation, causing the animals to lose their normally excellent sense of direction. It also prevents them from diving and feeding themselves.
Lost at sea, the flow of the surface currents directs the injured whales/dolphins downstream from the point of injury. Control over the swim path of the injured sea mammals happens because water is 700 times denser than air. The increased density induces a powerful drag (resistance) to swimming in any direction except downstream with the flow. Thus, surface currents quickly point lost whales and dolphins headfirst into the path of least resistance or least drag.
If the pod does not recover, surface currents are likely to deposit them on a sandy beach simply because current just happens to be the same energy that carries each grain of sand to build the beach in the first place. In general, whales/dolphins are directed to beaches that are building sand; not to beaches that are eroding.
Unable to navigate or dive and terrified by the pack of starving predators trailing them, the wounded whales/dolphins huddle together in a tight group for protection against sharks and killer whales. They swim downstream with the flow of the surface currents.
Land masses that extend out to sea opposing the flow of the surface currents, serve to trap sand, flotsam, seaweed, and lost sea mammals swimming with the flow. Cape Cod is the best example of such a natural trap in the United States. Cape Sorrel in Tasmania and Golden Bay in New Zealand are also natural traps for non-navigating whales/dolphins.
Capt. David Williams
Deafwhale Society, Inc.