Sharks pursue bloody victims using gel

November 14th, 2007 - 8:38 am ICT by admin  
The process, known as electroreception, involves sharks, rays and skates using a gel-like substance on their heads to pick up electrical current signals from their water environments.

This explains why sharks pursue bloody victims, even when other ‘easy target’ prey is around and the gushing blood obscures the shark’s vision and smell.

“The gel contains various proteins and salts, so it’s similar to mucus, only with a jello-like consistency,” said lead author R. Douglas Fields. “Basically, it’s shark snot,” he added.

The slimy substance plays a big role in hunting. It allows the fish to detect very faint electrical fields, which prey emit when they swim or bleed.

This new study is based on reports of swimmers towing wounded buddies to shore, with the shark still going after the injured person instead of the rescuer.

“With this gel, sharks can detect the strong electrical field produced by bloody salts,” explains Fields.

The findings, negate a prior study that claimed shark gel serves as a semiconductor, meaning that it generates electricity in response to temperature changes.

For their study, the research team extracted the gel from skate pores. The pores, which sharks and rays also have, are part of an organ system known as the ampullae of Lorenzini.

Skin membrane cells sense electricity, causing positively charged calcium ions to rush in. The charge moves through the gel before reaching nerves that send the electrical signals to the fish’s brain.

To prove this, the team inserted two silver wires into the gel and heated or cooled one end of the wire’s holder. Though this generated electricity, it was found that the electricity was simply caused by an electrochemical reaction between the silver and the gel. When non-silver devices were heated or cooled, no electricity was generated by the gel.

“So the gel is nothing but a conductor that allows electrical signals to move from the membrane to the brain,” said Fields.

These findings might lead to better shark repellent devices in the future.

“Now that the sharks’ electricity detection process is better understood, the information may one day lead to better shark repellent devices that can decoy sharks away from swimmers,” said Harold Zakon, a professor of neurobiology at the University of Texas. (ANI)

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