Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in Madang.

During our last research leg of the Bismarck and Solomon Seas, we were joined by Peter T. Madsen, a Ph.D. student from the Department of Animal Physiology at the University of Aarhus in Denmark. Sperm whales are extreme and impressive in every sense of the word. They dive almost continuously, day after day, year after year. These animals make regular passages between the dark, cold depths and the warmth of the sunlit surface. We know that food is the primary motivation for these vertical journeys, but do not understand how they do it Peter discusses the mechanisms behind one of the world's most impressive breath-holders.

Whales are mammals. Mammals evolved more than 200 million years ago as land dwelling animals that support their high metabolic rate, by continuously breathing air. In order to exploit the food sources of deeper waters, whales have to stay submerged at great depth for extended periods of time. Sperm whales are masters of this discipline as they may dive to depths of 2000 meters, holding their breath for an extraordinary, 1.5 hours. So how do they accomplish this? This can be accomplished in two ways, either by lowering oxygen demands or increasing oxygen storage. Sperm whales have evolved to perform both tasks. While diving, sperm whales lower their metabolic rate, slow down their heart beat and shunt blood mainly to their vital organs, thereby conserving precious oxygen.

In order to maintain vital bodily functions, the cells of the body must receive a continuous supply of oxygen. As in all other mammals, the transfer of oxygen from air to the cells is facilitated by a special protein in the blood called hemoglobin. Hemoglobin is a protein in the red blood cells that transports oxygen. Humans have a red blood cell volume of 2.8% of their total body volume, whereas sperm whales have a red blood cell volume of 12% of their body volume. This allows sperm whales to carry a much greater amount of oxygen in their blood, and thereby hold their breath for a substantially longer period of time compared to humans. The high concentration of oxygen stored in the muscle accounts for the distinctively dark red coloration of the muscle tissue of the sperm whale. When humans dive, a large amount of their available oxygen is stored in the lungs which accounts for 7% of the body volume. This is not the case in sperm whales, where the lung volume only accounts for 2.5% of the total body volume and thereby contributes insignificantly to the overall oxygen storage.

Peter T. Madsen

Photo: Chris Johnson

Given that both humans and sperm whales store compressed air in their lungs when diving, raises the question as to why sperm whales do not suffer from the "bends" as humans do, especially considering the length of time spent at depth by sperm whales. The "bends" (also called Decompression Sickness), is a condition that arises when a diver that has breathed compressed air at depth, returns to the surface to fast for the body tissues to expel the nitrogen gases accumulated during the decent. This leads to the generation of nitrogen bubbles in the tissue, a condition that can be fatal in humans.

The major difference between humans and sperm whales, lies in the fact that humans subjected to the "bends" are often scuba divers continually breathing air under pressure stored in the tanks carried on their back. Sperm whales only carry the one lung full of air inhaled before diving and their lungs collapse during a deep dive thereby moving their compressed air away from the lung tissue. Because of this they do not appear to be subject to the damage from bubble generation in the tissues, like humans are. There is no black magic behind the extraordinary diving capabilities of the sperm whale, only an animal that has managed to refine normal mammalian capabilities to an extreme, in order to exploit the food sources of the abyss.

Log by Roger Payne

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