Monday, July 27, 2009

Terrapins face risk in their quest to nest

Terrapin #2728 After successfully completing her epic struggle
Photo courtesy of Don Lewis

WELLFLEET — Don Lewis could barely contain the admiration he felt for a female terrapin that, despite being run over by a car last week, continued to struggle inland to lay her eggs. Her shell was badly cracked on both the top and bottom. She was bleeding, dehydrated and weak after spending the night crawling toward a spot to lay her eggs on a Lieutenant Island beach.

"Despite all that, she dug a hole through compacted gravel and laid 14 eggs and took the time to cover and disguise the nest. We would have rolled over and died," said Lewis, the chief financial officer at the National Marine Life Center in Buzzards Bay. Lewis is also licensed to recover, move and protect terrapins and their eggs and nests.

Diamondback terrapin

  • Medium-sized marsh turtle. Adult females range from 6 to 9 in. in length while males are 4 to 6 in.

  • Live in marshes bordering quiet tidal salt or brackish water areas and nest in adjacent upland sandy sites.
  • Found along the Atlantic coast from Massachusetts to Florida and along the Gulf coast from the Carolinas to Texas.
  • Listed as a threatened species in this state.
  • Nest twice a year in June and July.
  • Known to live 40 years.
  • Female can keep male sperm internally for up to four years.
  • The sex of the hatchlings changes depending on temperature with males developing if temperatures are below 82 degrees , and females developing above 86 degrees. A mix of males and females will develop between 82 and 86 degrees.

Source: Massachusetts Division of Fisheries and Wildlife

It wasn't the only crushed turtle he's seen this year.

Scientists call it "the killing grid." As if loss of habitat and increased numbers of suburban predators weren't enough, turtles get hammered as they travel to inland nesting sites by an even tougher opponent: cars.

"It is one of the major threats for our state-listed (under the state's endangered species act) species," said Lori Erb, turtle biologist with the Massachusetts Division of Fisheries and Wildlife.

Weather delays nesting

This summer, turtles were hit especially hard after a wet, cold June delayed nesting by a month, so that peak nesting coincided with peak summer traffic. That means more turtles getting hit as they attempt to cross roads bordering wetlands and creeks to upland nesting spots.

Normally Lewis finds one terrapin a year flattened by a car or truck. This year, he dealt with a dozen. "Turtles are like thermometers with legs," Lewis explained. Muscle activity in cold-blooded animals, like turtles, is dependent on chemical reactions that work much better in warmer temperatures.

After sleeping away six months of the fall, winter and early spring under the muck of saltwater creeks, terrapins rouse when water temperatures warm to 55 in late April. As the temperatures continue to rise, they have the energy to mate in May, develop eggs and nest in June, with the peak nesting season usually between June 20 and 25th, said Lewis.

But this June, air temperatures barely nudged out of the 50s. Turtles need 80 degrees to make the trek from marshes to upland nesting sites.

As a result, turtles of all species waited as much as a month past their normal nesting times for the sun. Unfortunately, when it did warm up, it was July 4th weekend, when other sun-loving species decided to make their annual migration to our shores.

"A lot of them were waiting and waiting. There was a bottleneck (of turtles carrying eggs), and then a burst of activity on the few nice days that came along," explained Erb.

Nests are undefended and hatchlings are easy prey for a number of predators, so survival rates are one in a thousand eggs living to become an adult. Turtles compensate for this low survival rate by living long lives and producing young over many years. Road kills hit the turtle population right where they are most vulnerable, because it is the females who tend to get run down.

Vehicles a major threat

Just how much of an impact roads have on the survivability of most species is unknown, but Erb said 30 percent of the Eastern box turtles they collect for study come from specimen that have been hit by vehicles.

Fisheries and Wildlife has created a BioMap and Living Waters Map that identifies large tracts of land, statewide, that are in need of conservation to preserve biodiversity. Erb said her agency is also working with other state and local agencies to come up with wildlife corridors, create barriers to fence turtles off from dangerous crossings, and install culverts under roads for safer passage.

But there are other threats from humans. The increasing use of stone walls to protect waterfront homes also denies turtles access to traditional nesting sites. And, as the Cape becomes more densely populated, predators like raccoons and skunks, which eat turtle eggs and hatchlings, are more numerous.

Lewis hopes to give terrapins a fighting chance by protecting nests with enclosures made of fine chicken wire fencing that are buried up to a foot deep in the sand, below the depth predators will burrow. On Lieutenant Island in Wellfleet, these pillbox enclosures dot the shoreline of what Lewis dubbed Turtle Point.

Diamondback terrapin nests on Lieutenant Island, protected by exclosures.
Cape Cod Times/Steve Heaslip

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