Deep-Diving Dolphins

Dolphins are very graceful as they jump above the ocean's surface to take a breath of air before diving deep into the water. As mammals, they must fill their lungs before they take the plunge. How are a dolphin's lungs capable of holding enough oxygen to enable such deep diving?

A research team recently studying dolphins was perplexed over how these mammals could dive as deep as they do—over 200 meters (650 feet)—and still have oxygen left. According to a report recently published in Science, such a dive should have required 25% more oxygen than dolphins' lungs hold.

The team attached video cameras to the dolphins and observed the dives. The cameras showed that dolphins use a series of stroke-and-glide motions that enable them to make efficient use of their aerobic capacities. Their lungs collapse progressively as they dive deeper, forcing the air out into the upper part of the respiratory system.

• Read CNN's summary of the report: "Marine mammals stroke-and-glide to depth."

Learn about the Problem

Basic gas laws affect mammal's lungs during a dive. Learn about the relationship between pressure and volume in Chemistry Gateways: Boyle's Law.

Think about the Problem

• To learn about lung volume in another mammal, see the activity Biology Gateways: Lung Capacity.
  
  
• Based on the information in this activity and in the CNN article, make a list of differences in how the lungs of dolphins and of humans behave during a deep dive. Which of these two mammals has evolution prepared for a life in deep waters?

For the Teacher: Extending the Problem

• Researchers have long been fascinated with dolphins. Students can find information about dolphins at the following sites:
  • Discovery Online's Ultimate Guide: Dolphins
  • SeaWorld's Bottlenose Dolphins
  • About Dolphins
  • The Dolphin Species Archive
  
  
  
• Students can learn about the physics of underwater diving at UNCW's Aquarius Underwater Laboratory site.
  
  
• Dolphins are often entrapped and killed in tuna nets. The "Dolphin Safe" tuna campaign tries to change the fishing methods of tuna fishermen. Students can learn more about the problem and the campaign at the International Marine Mammal Project. Just last month a judge struck down the use of the "dolphin-safe" label.
  
  
• Earthwatch Institute runs an expedition, Dolphins of South Africa, for collecting data to help determine whether the fishing industry is threatening the dolphins' survival.