Tracking Snapping Turtles Through The Seasons, Through The Mud

Photos by James Marshall.

Van Hook retrieves a radio-tagged snapping turtle from the mudflats around Merrymeeting Bay. James Marshall photo.

Snapping turtles. They are the bête noir of summer-camp lake swimmers, towering stars of Dr. Seuss fame, and, alas, fodder for fancy soups.

They also are something else, says Bowdoin senior Lucy Van Hook: misunderstood.

“Many people are afraid of snapping turtles,” she says, “but common snapping turtles are really very mellow. You can literally stand next to them with no problems.”

Van Hook ’06 should know. For the past two summers she has been radio-tagging and tracking the common snapping turtle, or Chelydra serpentina, throughout Merrymeeting Bay, where they are a fairly common sight. Although snapping turtle behavior has been studied intensively in freshwater ponds, little is known about their life on intertidal mudflats.

Working with Biology Laboratory Instructor Jaret Reblin, Van Hook is gathering information on the turtles’ nesting activity, population demographics, and the influence of tides on daily movement patterns in the Cathance and Muddy Rivers – which flow into Merrymeeting Bay.

The research is being directed by Assistant Professor of Biology John Lichter, who has been doing collaborative ecosystem research on Merrymeeting Bay for several years.

“No one really knows how snapping turtle populations are doing in Maine.”

“Merrymeeting Bay provides a unique system in which to study the influence of tides on turtle behavior,” says Lichter. “At low tide they can hunker down in the mud and stay hydrated while basking in the sun, and the diversity of vegetation and aquatic life gives them plenty to eat.”

“Our largest turtle is close to 40 pounds,” notes Van Hook, “and may be 90 years old.”

There is another reason for their research, she adds: “In 2002, Maine issued a ban on commercial harvest of snapping turtles, based on estimates of population sizes in Ontario. No one really knows how snapping turtle populations are doing in Maine.”

To begin collecting data on female population size and nesting habits, Reblin and Van Hook have been frequenting a sandy, gravelly area near a bridge where turtles come to nest.

On this June morning, the pair is returning to a spot where a female dug a small cavern the day before and deposited a cache of eggs. “Too bad,” says Van Hook, surveying the now-unearthed nest and broken, white eggshells. “Looks like something got them.”

Snapping turtles typically lay 20-40 eggs at a time, notes Reblin, but nests face heavy predation by skunks and raccoons. “Some scientists estimate it takes 3,000-6,000 eggs over a lifetime for a turtle to replace itself,” he says.

Van Hook uses a radio-signal detector to track turtles with transmitters glued to their shells.

One way the pair is gathering population data is to mark captured turtles with unique, identifying notches in the edge of their shells – before releasing them back in the wild. These marks will allow researchers to identify and record information about Merrymeeting Bay’s turtle population well into the future.

They are employing a more high-tech strategy to gather behavioral data. Over the past two summers, Van Hook has attached radio transmitters to the shells of 11 turtles. They then use radio-tracking equipment to find the turtles, and makes observations about their whereabouts and activities.

The small, resin radios are fueled with standard batteries and sport tiny, flexible antennae. Van hook says the radio-tagging process is simple. “We’re handling them anyway during nesting,” she says. “We mark and recapture as many as possible to assess population size. So, when we put them in a tub to do measurements, we just adhere the radio to the carapace with epoxy. It stays on for about a year.”

Once the radio transmitters are activated, the signal can be detected by antennae, allowing the researchers to locate the turtles and follow their movements through summer, fall, and into hibernation.

Van Hook received a Rusack Fellowship for her research last summer and a Doherty Fund fellowship for this summer’s work. She plans to continue the work with an honors project in the fall, then submit her data to the state. Hopefully, she says, the information will eventually be published in a professional journal.

“I’m a biology/environmental studies double-major,” says Van Hook. “I fully intend to go into field ecology work. I love this kind of research.”

Story posted Bowdoin College August 19, 2005