CAMBRIDGE – When Bill Gieze began working at Blackwater National Wildlife Refuge in the 1960s, the channel was still deep enough for an old military landing craft that was used to shuttle supplies to another site.
Today, he said, he has to be careful not to bottom out the refuge’s 17- foot camouflaged hunting boat. The channels have filled in as about 7,000 of Blackwater’s 17,000 marshland acres have eroded since the refuge opened in the 1930s.
One of the major contributors to that erosion is a beaver-sized relative of the rat from South America, the nutria. And Blackwater has a plan for the voracious root-eater — eradication.
“Right now, the nutria is the key player, the big boy doing all the damage,” Gieze said on a recent mild gray morning when he was out with a crew trapping and killing the animals.
Fur trappers first brought the large amphibious rodent to the Eastern Shore in the 1950s to boost the fur industry, but it’s hard to imagine anyone wrapping this ugly beast around themselves for a night at the opera.
Their dull-brown fur looks like a bad frost job from months ago. Four stained, bright-orange incisors half the length of a grown man’s pinky curl out of their mouths. And then there are the long and scaly rat-like tails that Gieze and his crew said sometimes freeze and fall off during the coldest of winters.
Congress has approved $2.9 million for a pilot program to wipe out nutria on the Eastern Shore, but that money has not yet been appropriated. Gieze and his crew were out last month as part of an existing program to estimate the nutria population on the refuge.
Five times in the last eight years, the animals have been captured and tagged in the fall. Hunters who trap them on refuge land between December and mid-March then report tagged nutria.
Gieze, a fire control specialist for the U.S. Fish and Wildlife Service at Blackwater, and his two assistants follow up in the spring, checking traps and “dispatching” captured nutria after tallying them as part of a two-week animal inventory.
They have a .22-caliber rifle on board the boat to shoot any nutria they find in their traps. Other animals caught in the traps are released unharmed.
As the hunting boat set out one morning last month, it carved through makeshift channel markings — little more than sticks in the 3- to 4-foot-deep black water. A light wind formed ripples on the water’s surface and carried the light-sulfur smell of the marsh.
A stretch of blue ribbon tied around a thicket of cord grass marked trap where the marshland meets the water. The first trap had been tripped but there was no animal in it. Of the dozen traps checked that morning, about half were found empty.
Stepping ashore on the marshland is like stepping onto an enormous queen- sized mattress — the surface springs below each step on the tight mass of roots that hold together the detritus of decomposing marsh vegetation.
It is the nutria’s voracious appetite for these roots that has decimated the marsh.
The damage done by nutria is evident: Holes spot the marshland in what is referred to as an “eat out,” with nothing but mud and upturned roots left behind by the foraging nutria. These holes soon grow as tides wash the river across the taller cordgrass that edges the marsh.
“It’s like a cancer – it starts in the middle and the last to go is by the river,” Gieze said.
At 45, the hair under Gieze’s brown Fish & Wildlife Service baseball hat has started to gray on the sides, but his mustache remains a sandy color. He has lived near the refuge his entire life and he shakes his head as he describes the marshland he has seen vanish in that time.
“It’s hard for me to tell you — it’s phenomenal how fast this thing went,” he said, his blue eyes framed with the lines that betray a lifetime on the water.
At the next stop, the trap held a nutria the size of a small pig. There are no known natural predators for the rodent. While an eagle or fox might kill a small one, by the time they have grown to full size after about six months, “there is no one touching them,” Gieze said.
This lack of natural population control, in addition to a non-stop breeding cycle, an extremely soft fur market and warm recent winters, has led to a boom in the population of the pest.
After shooting the vermin, the metal tags on its webbed hind legs were noted and the carcass was hurled by its rat-like tail down the edge of the marshland, food now for the vultures.
“That way, it’s not wasted,” a crewman said.