SunHerald.com
Study finds low dose of antidepressants in bull sharks
July 18, 2007
http://www.sun-herald.com/Newsstory.cfm?pubdate=071807&story=tp1ch6.htm&folder=NewsArchive2
A preliminary study by Mote Marine Laboratory found traces of antidepressants in a group of juvenile bull sharks tagged in Fort Myers last year.
However, researchers don't know how this will threaten the stocky fish.
The team released their findings last week in St. Louis, Mo., during the annual meeting of the American Elasmobranch Society -- a group devoted to the study of sharks.
Lead scientist Dr. Jim Gelsleichter said nine of the 10 sharks tested positive for sertraline, the active component in Zoloft. However, the values were about 75 times less than the daily dosage in a human, he said.
All of the fish had trace amounts of other antidepressants tested, but no contraceptives were detected.
"Right now, I'm not seeing anything that concerns me very much," Gelsleichter said. "It certainly supports having the study. The chemicals are there, but it's just a starting point."
Despite the findings, Gelsleichter isn't certain how human drugs in estuaries affect the inhabitants, since no widespread study exists.
Scientists have been testing juvenile bull sharks in the Caloosahatchee River to determine the health risks pharmaceuticals might pose. The study, which started in 2006, is funded by the Charlotte Harbor National Estuary Program and National Shark Research Consortium.
Many of the drugs are water soluble. In most cases, pharmaceuticals are introduced into coastal ecosystems by human excretion and wastewater discharge.
The bull shark, unlike its marine counterparts, can tolerate fresh water for extended periods. Adults breed in the brackish water of river mouths during the summer. Following birth, some will spend up to two years in the swallow rivers.
As a result, Gelsleichter said the sharks are regularly exposed to greater levels of wastewater chemicals.
To date, the team has captured 30 sharks, ranging in age from a few days old to two years. Scientists withdraw a blood sample to test for a dozen of the most commonly prescribed drugs. Each fish also is tagged with a silicone rubber disk that absorbs certain drugs before it is released.
Gelsleichter said the goal is to expand the list of human drugs to include anti-inflammatory and blood cholesterol agents.
But the weather hasn't cooperated this summer.
The study has taken a new, unexpected approach, as a lack of rainfall has scattered the concentration of bull sharks. Although frustrated, Gelsleichter said the drought could answer the question of whether chemicals remain in the water longer.
Scientists will place water samplers in the river next month to determine what human drugs are present.
"The real component of our study has started this year," Gelsleichter said.
KEEPING TABS
Anglers can also help the research. Those who frequent the Caloosahatchee River and catch bull sharks bearing Mote's unique tags are asked to remove the entire tag from the animal by clipping it off as close to the base as possible, storing it in a standard freezer in aluminum foil or a clean plastic bag and contacting Mote's Center for Shark Research at 941-388-4441, ext. 576.
You can e-mail Jason Witz at jwitz@sun-herald.com.
Staff Writer