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Nesting terrapins get commuter help with Port Mahon tunnels

Rock retaining walls hold back rising seas at Port Mahon Road in the Dover area, but they also inadvertently hold something else back: turtles.  


Turtles trying to reach their nests to lay eggs have to climb over these rocks, often getting stuck in the process.


One solution floated this summer to solve this problem is a pair of tunnels beneath the rocks. 





From the end of May to Mid-July, female diamondback terrapins are trying to lay their eggs. 


To make sure they get to and from their nesting areas safely, volunteers walk up and down Port Mahon Road, counting the turtles. They also look for any turtles stuck in the rocks.


As one turtle started to leave her nesting area to head back to the bay, she reached a couple of rocks, and then stopped.


“Yeah there is no way for you that way,” said Kara Okonewski. one of those volunteers. 


She picked up the turtle that was a little smaller than a dinner plate.


“She just laid. There’s nothing in her,” Okonewski said.


Okoniewski then placed her at the edge of a small beige tunnel that’s under a pile of rocks. 


The turtle seems a bit confused. Then, it trudges through the tunnel and back to the bay. 



Before these tunnels were put in at Port Mahon Road, the only option for turtles emerging from the bay was to climb over a wall of rocks, called a riprap revetment. 


“Ripraps were installed 20 years ago as coastal roadways started to see erosion from climate change, sea level rise. They’re widely accepted as a stabilization technique,” said LaTonya Gilliam, a group engineer for environmental stewardship with the Delaware Department of Transportation.


Port Mahon’s riprap was installed in 2003. In addition to causing issues for the turtles, it’s also having issues of its own, Gilliam said. 

Credit Katie Peikes / Delaware Public Media
Delaware Public Media
The riprap revetment prevents rising seas from flooding Port Mahon Road.


“Staff has to come out every once in awhile and make repairs,” she said.


The most recent repair was in January after a tropical storm


“Now engineers are starting to rethink how we stabilize our coastal road,” she said.  


While reevaluating the riprap, they noticed the turtles continue struggling to navigate it. In the summer of 2015, the Delaware Department of Natural Resources and Environmental Control responded to a call about a dead dolphin at Port Mahon. When they arrived, they saw dozens of turtles stuck in the rocks. 


The turtles have a high fidelity to their nesting areas, so they’ll try to cross no matter what is in their way, said Holly Niederriter, a wildlife biologist with DNREC.


“They come back to the same nesting area every year, so for them to get blocked from that nesting area, they’re pretty persistent, they’re gonna push their way through,” Niederriter said.


Even though the riprap is more than 4 ft. tall in some spots, the turtles still try to climb it to get to their nests or back to the water.

Credit Jessi Rando, a volunteer watching for turtles for DNREC.
Jessi Rando, a volunteer watching for turtles for DNREC.
A turtle tries to climb the rocks at Port Mahon Road.

“There’s big crevices between the rocks and the turtles are climbing up and instead of getting to the other side of the wall, they’re falling straight in,” Niederriter said.


DelDOT then designed an 8 ft. long oval-shaped tunnel made of reinforced concrete. They placed two of them along Port Mahon Road where turtle traffic has been reported more heavy, hoping the turtles would use them.


But Chase McLean, a research assistant with the Division of Fish & Wildlife, said the turtles are not taking to the tunnels as he’d hoped.


“We had hoped they would forego trying to climb as often and move along the rock wall towards the tunnels,” McLean said.


That may be because turtles are so faithful to their nesting sites that it’s just hardwired into their brain to get there by any means possible and not search for alternatives. 


Two weeks ago, DNREC reported it had only recorded one terrapin using a tunnel. 


“We knew the turtles were still just going to climb over the rocks and they were gonna need something to guide them towards the tunnels, but all parties are hesitant to do anything like that here because the rocks are so close to the road,” Niederriter said. 


DNREC told Delaware Public Media that updated data on turtles using the tunnels isn’t ready yet. They’re still waiting for some data sheets from volunteers to give them a more complete picture. 

Credit Katie Peikes / Delaware Public Media
Delaware Public Media
A turtle tunnel at Port Mahon Road.


In an email, McLean said this year got off to a later start for nesting than in two previous years at Port Mahon.


“We have seen a distinct increase in the proportion of terrapins getting stuck in the rocks as compared to two previous years,” McLean said. “It is still too soon to get an idea of total number of terrapins we have had on, but we did see a reduction in the numbers seen on land between 2015 and 2016.”


He continued, “So far this season we have had a few individuals use the tunnels without assistance, but we are noticing that they are having trouble locating the tunnels without help from volunteers.” 


They then figured out a way to channel the turtles to the tunnels a couple of weeks ago, adding two 15-foot pipes to each side of the tunnels.


They also placed geotextile material over a couple of sections of the rocks that the turtles can grip to climb over. 


“As of now, I do not have any data to speak to the success of the piping added to help with this issue, but during experiments conducted by myself before their installation they did funnel the turtles to the tunnels,” McLean said.


McLean said it’s a little late in the nesting season to gauge how successful this is, however, but he said DNREC and DelDOT hope to deploy these methods on a larger scale next year.


And removing the riprap is not an option, Gilliam said. If DelDOT removed it, the waves could scour the road, eroding it away.


“The riprap right now is the only thing that’s keeping the roadbed in place,” Gilliam said.


There’s also no chance DelDOT would relocate the road, because it could cost millions, Gilliam said.


But the state is working on a long-term “living shoreline” solution that would allow them stabilize the shoreline and make it safe for turtles. 


That’s contingent on DelDOT and DNREC getting funding for the full project. Gilliam said DNREC has money for a concept design, but neither agency is ready to foot the bill for finalizing a design or construction.


The good news, McLean said, is that so far this year, no turtles — at least based on the volunteer data they have so far — have died trying to get over the rocks.


“We have a much larger group of volunteers this year. They’re doing an excellent job of pulling the terrapins from the rocks,” McLean said.


He said that goes to show even if the turtles aren’t using the tunnels, there’s enough human helping hands to allow the turtles to successfully complete their nesting cycle.