Terrapins View Crab Pots as Playgrounds, Not Death Traps

If it were a reality show, it might have been called “Real Terrapin Behavior in Virginia.”

For weeks this spring, biologists filmed and watched the 24/7 exploits of groups of diamondback terrapin turtles that were rotated through one-week stints in an 18-foot water tank. Fortunately, they could fast-forward.

“We can watch an hour in 8 minutes,” said David Stanhope, field research manager with the Virginia Institute of Marine Science Center for Coastal Resource Management.

While turtles may not make for action-packed viewing, the recordings produced eye-opening information about terrapins — especially when it came to their interaction with crab pots.

At night, they slept on them.

In the daytime, the pots became playthings.

“They would cruise around the pots, cruise into the pots, then back out, over and over and over again, like it was a little playground,” said Randy Chambers, a biology professor at the College of William and Mary who has studied terrapins for years. “They do not have any fear of a crab pot at all.”

That’s a problem for terrapins in Virginia, where they are considered a species of concern.

While the crab pots in the tank had wire “chimneys” that allowed turtles to escape, pots in the wild effectively trap — and drown — terrapins. Nowhere in the Bay is it legal to aim to catch terrapins, but they are often taken by accident in pots. In fact, Chambers believes that crab pots in tidal creeks are the largest source of mortality for juvenile and adult terrapins in Virginia.

Terrapins live in brackish creeks adjacent to coastal marshes, and are found from Texas to Cape Cod. Historically, they were abundant and were hunted for food, with much of the harvest taking place in the Chesapeake. They were fed in large numbers to slaves and, during the Revolutionary War, to colonial soldiers.

But turtles have low reproductive rates and could not sustain heavy harvest pressure. Coastal development also impacted marshes and nearby dunes where terrapins lay their eggs. Today, they are considered endangered in Rhode Island, threatened in Massachusetts, and a “species of concern” in Delaware, Virginia, North Carolina and Georgia.

It’s hard to say with certainty that terrapin numbers are declining in Virginia because comprehensive surveys are lacking. But in several creeks where Chambers and his students have studied terrapins for years, these turtles have declined in numbers — or disappeared altogether.

In Queen’s Creek, a small York River tributary, Chambers and his students estimated the turtle population was nearly 200 in 2001. Seven years later, their estimate was 50. “Three years after that, we caught three turtles,” Chambers said.

A string of crab pots dotted the length of the creek, and Chambers talked to the crabber who fished them. The crabber said he found, on average, about one drowned terrapin a week, Chambers said, “which doesn’t sound bad, but when multiplied over the entire crabbing season, and by 10 seasons, it ends up being a fairly large number.”

It is hard for terrapins to replace that rate of loss. Only about one out of 20 eggs that are laid will hatch a turtle that survives its first year, and only one in 200 will reach reproductive age, said Robert Isdell, a graduate student at VIMS.

Isdell is mapping terrapin populations so they can be monitored to see if populations remain stable, or disappear. In some places, he thinks they’re already gone.

One Eastern Shore creek, he said, had “just beautiful, beautiful habitat. But it also had a higher density of crab pots than I’ve seen anywhere. And I didn’t see any terrapins.”

In Maryland, commercial crab pots are prohibited in tributaries, which typically contain the brackish water and marshes terrapins prefer. Recreational crabbing is allowed, but those crab pots are required to have a bycatch reduction device, or BRD, which restricts the openings so crabs can enter, but terrapins are kept out.

Several other states along the coast, including Delaware, also require BRDs, at least in certain habitats.

In Virginia, commercial crabbing is allowed in creeks, and neither commercial nor recreational crabbers are required to use BRDs on pots. Commercial crabbers have been hit with numerous restrictions aimed at protecting blue crabs in recent years, and regulators have been reluctant to add more rules to protect terrapins without clearer data that crab pots are causing a decline, or that BRDs would help turtle populations recover.

BRDs usually cost less than a dollar, but each crab pot needs four, so the expense adds up for a crabber that may fish hundreds of pots. Some watermen also worry the devices could reduce the catch, though proponents say they have little, if any, impact.

Some scientists have suggested requiring BRDs only for recreational crabbers. Recreational pots may be checked less frequently than commercial pots, increasing the likelihood that trapped turtles will be drowned.

The experiment in the VIMS tank attempted to explore another tack for turtle protection. Biologists used different colored pots to see if certain colors might repel turtles — painting, or simply buying different colored pots, would be cheaper than requiring BRDs.

Unfortunately, the tests showed that terrapins played with crab pots regardless of their color. Chambers said the turtles appear to be naturally curious and attracted to any type of structure.

“This inquisitive mentality unfortunately, it is one of those bad behaviors for a species that end up getting it into trouble,” Chambers said.

It can, in fact, lead to trouble for whole groups of turtles. In the tank, terrapins showed communal behavior, often clustering together to sleep and following one another around the tank — and into the crab pots.

“It seems that once one goes in, the other guys follow along,” Stanhope said, “so there is some kind of herding going along.”

This herding behavior can be bad news for terrapins, and explain why a single pot occasionally drowns many — sometimes dozens — of terrapins at a time.

“There are areas where you don’t find terrapin anymore,” said Donna Bilkovic, a researcher at VIMS who’s also been involved with the project. “That could be part of the reason.”

The scientists haven’t totally given up on using color to help the turtles. This summer, Chambers and student Olivia Trani are testing different colored BRDs on crab pots placed in tidal creeks. Colors may not affect turtles, but Chambers wonders whether certain colors might attract crabs. If so, that could induce crabbers to add BRDs on their own, without regulations.

While that won’t solve all of the problems facing the terrapins, it could help give remaining populations a better chance of hanging on.

By Karl Blankenship
Bay Journal News Service