Man-made barriers like dams help divert water and prevent flooding in the First State. Many of them were also built as part of historic mill race ponds.
Some of them in the Inland Bays watershed, however, create a challenge for American eels trying to make their way to a freshwater habitat this time of year. Scientists from the Center for the Inland Bays have been experimenting with various devices to help eels bypass the dams.
As hundreds of thousands of young American eels arrive in Delaware’s Inland Bays, they encounter a roadblock: dams.
The dams in the Inland Bays watershed are part of historic mill race or recreational ponds, said Janice Shute, the state dam safety engineer for Delaware’s Department of Natural Resources and Environmental Control.
“There was just a little area where they had the water coming through and they had a water wheel on the mill, and they would use that pond to turn the water wheel to generate power,” Shute said.
Last October, staff from the Delaware Center for the Inland Bays installed a long plastic tube called an eelway, near Burtons Pond Dam – one of three the center has experimented with since 2005 - hoping the eels will use them to bypass the dams. The other two are around Millsboro Pond Dam and Betts Pond Dam.
But the center doesn’t have much data on whether these devices serve their purpose, so environmental scientist Andrew decided to track it over the last few weeks, at Burtons and Betts ponds while the eel immigration is at its peak.
“If we can get eels up and over that dam, then they have all the freshwater habitat in Burton’s Pond and beyond,” said McGowan, at the first sampling site: Burtons Pond Dam.
McGowan wades into Burton’s Pond until he’s almost waist-deep. He approaches an entrance to an eelway and pulls out a piece of unfurled rope connected to a potted plant. It’s called an eel mop - and to eels, it looks like underwater grass.
If eels are in the eel mop, it means they were right next to the tube but either couldn’t find it or decided not to use it.
McGowan admits it’s not a perfect system of measurement.
“The difficult part is you don’t know how effective the eelway was because it’s challenging to get the exact number of eels at the bottom end of the dam without influencing how many eels can actually use the device,” he said.
McGowan and Dennis Bartow, another scientist with the center, work to untangle any remaining eels.
They put them into a bucket filled with water, then they pour the sample into a net to count them. After that, they release those eels on the other side of the dam.
A few miles upstream of Millsboro, they find older eels in their devices at Betts Pond Main. Here, they have an eelway made out of prefabricated aluminum, and use a solar panel and a small garden pump to distribute water from the pond onto the surface of the metal.
“Water runs downstream and that acts as the attractant to sort of entice the eels to come onto the platform, come up onto the pond,” McGowan said.
McGowan and Bartow visit these ponds twice a week. At Burtons on Thursday, March 1, the day Delaware Public Media accompanied them on their sample, they saw 12 young eels in the eel mops, and none in the eelway.
“Burton’s Pond has a more concrete spillway,” McGowan said. “It’s more of a flat sandy bottom. There is a lot of glass eels at that site, particularly today. Here – Betts Pond is more of a rocky bottom, a lot of larger boulders and a little bit of a higher flow.”
They’re always thinking of ways to improve their devices, which they discussed in the car between ponds and on the way home.
MCGOWAN: “Eel mops are like a totally easy way to pass eels.” BARTOW: Thinking of getting a real big hank of it, having it drape over the spillway, come up through it MCGOWAN: Something of that nature, something that lets them go one way, not the other.
Bartow later said in an interview with Delaware Public Media, “If you had something hanging down from where the water comes over from where it came down, any of the eels that got up from the lower area could crawl up to the pond.”
Bartow and McGowan noticed a lot of the eels seemed to congregate around the edges of the ponds, and are looking at moving an eelway to the side.
McGowan bought a battery, solar charger and new pump earlier this week to change the design of the eelway at Burton’s Pond. This will help water to continue running through the eelway, regardless of if the water levels of the pond change, he said.
As they continue to ponder what they can do to help the eels navigate past the dams, Burton’s Pond Dam is scheduled for repairs in 2021. It’s part of a state program to help bring older dams up to code, said DNREC’s Janice Shute.
“The design standards of today are to build the spillway for a much larger storm than many of these were built to in the past, so we’re trying to bring them up so they can pass these larger storms and not overtop and fail,” Shute said.
It’s too early to tell how these repairs will affect the eels, but the Center for the Inland Bays says if staff can work with the state so both the eels and the dams benefit, they’re open to that.
