Bull sharks can be fearsome creatures, blamed for biting more humans than any other shark species. Traveling the world’s tropical and sub-tropical oceans, growing as large as 10 feet, they are one of very few sharks that also thrive in freshwater – and the 150-mile-long Indian River Lagoon may be their most important Atlantic nursery grounds.
Here they spend the first five to seven years of their lives and serve as an indicator species of the health of east-central Florida’s main waterway.
Now, a visiting professor at Florida Institute of Technology in Melbourne is embarking on a research study using the relatively new technique of extracting environmental DNA from lagoon water samples to help fill in gaps in scientists’ knowledge about bull shark life history and reproduction, and how the species responds to algal ‘super blooms’ and climate change.
Armed with more than 80 water samples collected several weeks ago by some 26 groups of elementary, middle school and high school students from New Smyrna Beach to Jupiter, Dr. Jeff Eble and colleagues plan to isolate genetic material such as feces and scales sloughed off by bull sharks to detect their presence in remote areas of the lagoon where traditional shark sampling methods are not possible.
Using DNA analysis, the scientists don’t have to set out any nets, bait any hooks, or install acoustic receivers; they don’t ever have to get wet or handle any sharks, and there’s no mortality among their test subjects.
“We are starting with bull sharks,” Eble said, “because they’re there, because they’re cool and because we can. We are going to test our protocols and provide decent data on distribution and habitat use. We know this is important nursery habitat. How will they respond to the next super bloom? How will they respond to climate change?”
Previous scientific studies using traditional sampling methods have shown that bull shark pupping grounds are expanding north to the estuaries of the Carolinas – likely in response to warming waters from climate change. Eble says DNA data will complement that work.
And the scientist doesn’t intend to limit his research to bull sharks. Using a technique called meta-barcoding, Eble said, he can detect more than one species from a water sample and gain a better understanding of fish communities and distribution.
“We’ll get bull shark data, prey data, other shark data – [learning about] the competitive behavior among species – and get regional patterns of fish distribution in the Indian River Lagoon,” he said. “We can then track those communities over time. That’s when we’ll have the real power to track the effects of algal blooms on the whole community and to track how well restoration is working.”
Eble said his work got a big boost from the Oct. 4 “A Day in the Life of the Lagoon” event where some 1,800 students from first grade through high school with teachers and volunteers collected water samples over the entire length of the lagoon.
“We could not have covered that ground and gotten that science,” he said. “The involvement of all these students and volunteers allows us to ask questions we couldn’t do before.”
Currently, the professor and his colleagues are readying some frozen DNA samples for examination and testing, with some early results expected this winter.
