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    SEPTEMBER 8, 2005
 
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‘Jaws’ breaker

A Temple professor is trying to create a shark repellent patterned after one occurring naturally in a particular species
of fish

JohnWilliams
Williams

As a young boy growing up in Western Australia, chemistry professor John R. Williams developed what has become a lifelong fascination with sharks.

“I can always remember being on the beach in Perth and seeing some weekend fisherman go by carrying a rifle,” Williams recalled. “I thought to myself, ‘That’s unusual because you don’t shoot fish.’ So I went over and asked one of the guys why he needed a rifle and his comment was, ‘Son, you never want to be in a boat with a live shark. They will take a chunk out of your arm or leg.’

“Every summer weekend when I was growing up, small planes would patrol up and down the coast looking for sharks,” he added. “Pilots could see the shark’s black outline against the light sandy bottom from the air. The pilots would relay the information to the lifeguards on the beach who would sound the siren warning swimmers to get out of the water. The lifeguards would row out in boats and scare the sharks away.”

That childhood experience has developed into a mission to try and prevent deadly shark attacks and confine them to movies such as Jaws. For the past 10 years, Williams has had an active research program in which he uses derivatives of cholesterol, the most common animal steroid, to make a class of compounds called mosesins and pavoninins that have been known to act as shark repellents.

“Several years ago, I read a paper by researchers that I knew quite well at Columbia University,” Williams said. “They had isolated a series of steroids from a particular species of fish that inhabits the Red Sea and South Pacific. These particular steroids, which have a sugar molecule hanging off them, have natural shark-repellent properties.

“Anything that has a steroid in it I’m interested in because we’re always looking to make potentially useful molecules,” he said. “We want to see if we can make them, as well as new structures with superior biological properties that are cheap to make.”

sharkdive
Photo courtesy John R. Williams
Professor Williams and students from the Sharklab in the water observing sharks at the Bimini Biological Field Station in the Bahamas.

Starting from a plant steroid called diosgenin, Williams and a graduate student, Hua Gong, have synthesized Pavoninin-4, as well as the cholesterol derivative without the sugar molecule called Pavoninin-5 with the help of graduate students Deping Chai, Jim Bloxton and Bill Solvibile. In the summer of 2003 he tested similar analogs — structural derivatives of a parent compound — on reef sharks with the help of Sam Gruber at the Bimini Biological Field Station Sharklab in the Bahamas.

“You have a long rod with a fish head on the end of it and a tube running through it to squirt the compound into the shark’s mouth when it tries to bite the fish head,” Williams said. “When the shark decides to take the fish, there’s a big splash of water and you can’t really tell when you squirted the compound if it’s gone into the shark’s mouth or into the water. There’s so much white water from the splashing it’s really difficult to tell.”

Williams explains that the sharks need to ingest the compound so that it goes through their gills.

“Apparently, there is some receptor on the shark’s gills that reacts to the steroid,” he said. “This is how the fish does it in nature. When the fish feels threatened by the shark, it disperses the natural compound into the water and the trailing shark has to swim through it, tastes it as it ingests it, and then is repulsed by it.”

Although those early tests were “somewhat inconclusive,” Williams said he thinks the researchers are on the right path. He plans to return to Bimini with smaller equipment in the future to retest his new compounds that are based on the natural shark repellents.

“We have a couple of simple analogs that look good, but we need to do the bioassays, or tests with the sharks, again,” said Williams, whose research group is synthesizing new compounds this summer for him to test. “So, for now, we can’t really say for certain how good these compounds are going to be.”

Williams said that potentially, if successful, down the line these compounds could be something that could be added to sunscreen to help people ward off sharks in the water when swimming in the ocean.

“Or for people who really feel scared swimming in the ocean, it could be put in a container that they wear around their waist, so when squeezed, the repellent would be released into the water around them, much like the fish does naturally,” Williams added.

Williams says he is trying to successfully duplicate nature by making a natural compound that is much simpler and much cheaper to produce.

“We have a nice, inexpensive starting material,” Williams said. “Hopefully, we can modify it sufficiently to make it biologically active.”

- By Preston M. Moretz

 

 


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