By Jim Waymer
May 5, 2017
Florida Today
Researchers studying our closest relatives that live in the Indian River Lagoon have delivered a grim diagnosis: our local dolphins are ailing under a relentless barrage of pathogens, mercury and pollution. Half suffer chronic illness, and biologists say we had better pay attention to their plight, or we may be next.
“I think we may be seeing a parallel to what’s happening in the human population,” said Greg Bossart, chief veterinary officer at Georgia Aquarium, who co-authored two recent lagoon dolphin studies. “This is Florida’s 400-pound miner’s canary. They’re really trying to tell us something, but for some reason we’re not listening very closely.”
Biologists say we should heed the warning because dolphins top the food chain and eat the same fish we do.
The top can be a perilous place within the 156-mile-long estuary. The recent findings regarding Indian River dolphin are the latest evidence that the lagoon – a unique Florida ecosystem – is in peril.
Local dolphin test at among the highest blood mercury levels ever measured in the species. The heavy metal taxes dolphins’ immune and neurological functions, heralding similar health risks for us.
Biologists don’t know how much mercury a dolphin can bear.
“We can’t give them an IQ test,” said Adam Schaefer, a researcher at FAU-Harbor Branch Oceanographic Institute in Fort Pierce, who coauthored the study. “We’re really just scratching the surface. These guys are exposed to a lot of other pollutants.”
Mercury is among the most toxic elements in humans and marine mammals because it builds the further it goes up the food chain. Symptoms of mercury poisoning range from stomach discomfort to brain damage, birth defects and death. Mercury interferes with human brain development. Symptoms in adults intensify if the body accumulates mercury faster than it can be shed.
A 2006 study found an estimated 300,000 to 600,000 American children suffer reductions in IQ related to mercury poisoning.
The FAU researchers say the mercury levels are higher in dolphins and fish in the northern Indian River Lagoon compared to elsewhere in Florida. The reason is because bacteria in the sulfate-rich muck and salt marsh transform mercury into a much more toxic, more readily absorbed compound called methylmercury.
“It’s both the species that they’re eating and the area where they’re feeding,” Schaefer said. “We’re seeing animals with the highest concentration cluster together in their social network.”
The study, published recently in Marine Mammal Science, was conducted by researchers at Harbor Branch; Georgia Aquarium; Colorado State University; National Oceanographic and Atmospheric Administration; and the University of Miami.
Dolphins’ social groups share similar mercury levels
The researchers drew blood samples from 98 lagoon dolphins between 2003 to 2007 and from 2010 to 2012, as part of a longer-term study comparing dolphins in the lagoon with dolphins in Charleston, South Carolina.
A 2011 estimate puts the lagoon’s dolphins at 662 individuals. They spend most of their life in the lagoon, hanging out where the fish are and hunting in packs. A long lifespan makes them good indicators of overall ecological health. To keep track of them, researchers maintain a photo catalog identifying the dolphins.
“It’s the first time that anyone, we know of at least, has integrated social network data into environmental exposure,” Schaefer said of the mercury study.
A study in 2014 by Schaefer and other researchers found that people who ate lagoon seafood once a day were almost four times more likely to have mercury levels in their hair higher than federal guidelines. Levels found in women were just below the federal guidelines but about five times higher than the average for U.S. women of childbearing age. People from Martin County had the highest mean hair concentrations of mercury, followed by Brevard and Palm Beach counties.
For most fish species, researchers find similar mercury levels that lagoon fish had 16 years ago, when the Fish and Wildlife Research Institute conducted a statewide study of mercury in fish.
“I think for a lot of species it’s probably relatively stable,” said Doug Adams, a research scientists with the Florida Fish and Wildlife Conservation Commission.
FWC’s mercury findings echo Harbor Branch’s.
“We found that seatrout from the northern part of Mosquito Lagoon, which has less human urbanization, had comparatively higher levels than farther south,” Adams said.
Since 2003, a team of Harbor Branch and other researchers have examined and released more than 360 bottlenose dolphins, 250 of them from the lagoon and the rest in Charleston Harbor, South Carolina. They find only half of those dolphins are clinically healthy, and the lagoon dolphins are worse off.
They measured mercury in blood and skin of lagoon dolphins at more than four times higher than those found in dolphins in Charleston Harbor.
Dolphins studied near Merritt Island, especially, seem in poor health. And the researchers point to water tainted by partially treated sewage and runoff as the possible cause.
Mercury levels stabilizingThe good news is that blood mercury levels in the lagoon dolphins’ blood, although still high, have shown a significant, steady decline over the past decade, according to a 2015 study by Harbor Branch and other researchers. That may be because of emissions reductions, a shift in the prey lagoon dolphins eat or other reasons, the researchers said.
Biologists aren’t sure what healthy mercury levels in lagoon dolphins should be, but they know the problem isn’t going away anytime soon.
“Even if we stopped polluting today, there’s going to be a lag effect, because mercury is ubiquitous,” Shaefer said.
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