Nosing Around the Shark's Nose

By Ellen Kuwana
Neuroscience for Kids Staff Writer
February 23, 2003

Did you know that sharks have a sixth sense? Like humans, sharks have five senses: smell, taste, touch, see and hear. They detect smells through two nostrils on the underside of their snout (they do not use their nose to breathe, as humans do). They sense vibrations (such as those from a wounded fish struggling in the water) using a "lateral line system." The sixth sense is the ability to detect electricity. All animals emit an electrical field. The ability to detect this electrical field allows a shark to find hidden prey. Specialized gel-filled pores in the shark's nose, called ampullae of Lorenzini, are responsible for this formidable sixth sense. Recently, a California researcher has discovered another impressive feat that these specialized pores perform.

The shark's six senses combine to make sharks great hunters. To track their prey, sharks find areas of the ocean teeming with fish where waters of different temperatures meet (called "thermal boundaries"). How do they sense the water temperature so well?

According to physicist Brandon Brown of the University of San Francisco, sharks are "the most temperature-sensitive creatures we know." Dr. Brown has discovered that the gel in those pores create an electrical current in response to differences in water temperatures. These electrical currents in turn cause electrically sensitive nerve cells to fire. This is how the shark detects small changes in water temperature, thus leading it to waters rich in fish.

In the lab, Dr. Brown warmed test tubes of the gel. He found that a difference in temperature as small as one degree Celsius resulted in a voltage as large as 300 microvolts. The experiments suggest that the gel could enable the shark to detect water temperature changes as small as 0.001 degrees Celsius.

How did Dr. Brown obtain this gel? He is known around the Bay Area coastline for being interested in sharks, so whenever a shark dies at an aquarium or washes up on shore, someone calls him. Getting the gel, it turns out, is easy! Just push down on the snout and the gel oozes from the pores. This Jell-O-like substance is then collected and whisked back to the laboratory.


Photo credit: Dr. Douglas Kellogg, University of San Francisco

Did you know?

Tagging studies have surprised shark researchers by showing that great white sharks spend up to 5 months away from shore. Researchers thought that great whites spent all of their time near shore, in waters within 30 meters of the surface. The new data suggest that these predators spend plenty of time 300 to 500 meters down. It makes sense that having sharp senses would be a big advantage in deeper, murkier waters.

References:

  1. Shark Sense: Gel helps animals detect thermal fluctuations by Jessica Gorman, Science News Vol 163, No 5, February 1, 2003, page 68.
  2. "Special Gel Helps Sharks Sense Cold," Scientific American, January 30, 2003.
  3. Brown, B.R. Sensing temperature without ion channels. Nature Vol 421, page 495. January 30, 2003.


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