The best way to catch a bog turtle is a technique called "muddling." This turns out to be just as messy as it sounds.

Scientists plunge their hands into swamp mud as thick as chocolate ice cream and spiked with sharp-edged plants. They feel around blindly, hoping to touch a turtle's four-inch-long shell.

"It all depends on your tolerance for insects and getting scratched on your arms," said Scott Smith, a biologist standing knee-deep in a bog here in Harford County northeast of Baltimore. "I just kind of blot out the heat and the bugs and the scratching."

Smith, who works for the Maryland Department of Natural Resources, has a job description that is deceptively simple: He counts animals.

Across the Washington region, biologists such as Smith are conducting censuses in mountain streams, bat caves and muddy bogs. Their quarry can be as small as a tiny worm and as big as a 300-pound mother bear.

The work is hard and often frustrating, but scientists say it is crucial: No decisions about hunting and endangered species can be made before somebody actually counts noses in the wild.

"If you don't know where they are, you can't protect them," said Dan Feller, another Maryland biologist. "It just takes that time to go out and locate them."

Just last week, scientists recommended that Virginia and Maryland continue limiting crab harvests, based on results of the annual Chesapeake Bay blue crab survey. The survey, actually four separate counts, used a variety of methods, including dredging crabs out of the mud where they hibernate, to determine that the crab population had increased slightly last year.

This fall, Maryland will rely on a totally different kind of animal survey to prepare for its first black bear hunt in 50 years.

State officials have said that the state's bear population, which was estimated at between 166 and 437 in 2000, is big enough to support a hunt in which 30 bears would be killed.

But to arrive at this estimate, somebody first had to count bears. One technique was using molasses to lure them to a tree stump, then stringing barbed wire around it to catch hairs for DNA samples.

Another approach employed by Maryland biologist Harry Spiker might be called The Hard Way: In the winter, he barges into dens where mother bears are hibernating with their cubs.

"If they're in a rock pile, I stick my head in the rock pile," Spiker said.

Sometimes, he said, the mother bears get angry and "bluff-charge," feigning an attack to drive him away.

"You give the bear space. Don't run, don't make any loud noises," Spiker said. "Just slowly back away."

Just as biologists and their survey results might give this hunt the green light, they have shut down others when an animal population falls too low. In the mid-1990s, surveys of Canada geese in Maryland found their population had dropped sharply, and hunting on the Eastern Shore was stopped for several years.

When dams and overfishing depleted the shad population, it took extraordinary measures to revive the once-common fish: A "fish lift," or water-filled elevator, was built to help the spawning shad over the Conowingo Dam on the Susquehanna River near Port Deposit, Md.

To ensure that the strategy is working, though, someone has to count the fish. That job fell to Michael Martinek, a trained biologist, and Francis Kenny, an erstwhile welder who answered a help-wanted ad.

As the shad run upstream to spawn -- and over the top of the dam in the fish lift -- they pass a plate glass window. In a darkened booth on the other side of the window, Martinek worked a clicker to count American shad, and Kenny counted gizzard shad -- a nearly identical species.

The fish come by in the dozens or the hundreds, sometimes adding up to tens of thousands in one 12-hour shift.

"The first blast is the worst," Martinek said in a recent interview in his booth.

The job can be even tougher for biologists surveying animals that are scarce to begin with -- and make themselves scarcer when humans approach.

In Maryland, there is the hellbender salamander, a two-foot-long slimy creature that lives under boulders in the Casselman and Youghiogheny rivers in the state's western panhandle.

Feller, the Maryland biologist, and an assistant use a long lever to pry up the rocks. Then they quickly sweep the speedy amphibian into a net before it can disappear.

"Once they swim, that's it," Feller said. "You've pretty much lost them."

Every salamander counts. On one recent trip, Feller's team lifted about 5,000 rocks and caught only 28 salamanders -- for a rate of one hellbender per 180 boulders.

But, Feller said, the hellbender is a picnic compared with looking for freshwater mussels. These extremely rare creatures live in mud at the bottom of small streams and show themselves only as little circles in the bottom, perhaps an eighth of an inch across.

They can be found by snorkeling through the mud or by peering down through a "viewing bucket" with a clear plastic bottom. Six or eight hours of snorkeling leaves Feller freezing, and a full day with the viewing bucket gives him a headache from eye strain, he said.

Still, the mussels can elude him.

"You'd be lucky to see one" in a day of searching, he said. "I've actually spent . . . 40 to 50 hours without finding one."

The hunt for the bog turtle, though, might just be the most miserable.

The turtle is listed as "threatened" in Maryland. It lives only in small and isolated wetlands and can live to age 60 without growing more than five inches long.

Biologists claim they can tell good bog turtle habitat by the smell -- something like rotten eggs -- and the squishy mud, which can suck boots right off your feet.

And in a good turtle bog, there are probably also ticks, wolf spiders, snakes and snapping turtles that could bite off a finger.

"It gets a little scarier the deeper you go," said Maricela A. Constantino of the U.S. Fish and Wildlife Service.

But on this day, when Smith, Constantino and four others were searching in the bog, the muddling paid off.

"Turtle!" yelled Meredith Whitney, a graduate student working for Smith.

She held up a small brown creature with an orange patch on its neck. The turtle waved its feet.

Soon, the turtle would be measured, marked and returned to the mud. But, for the moment, it was a time of celebration, as the other turtle-hunters slowly squished over to ogle Whitney's struggling catch.

"It's like finding a little jewel," Smith said afterward.

"These are really rare, and they're really cool," he said. "And every time you find one, you get the same sensation."

Meredith Whitney searches a Harford County swamp for bog turtles, which are listed as "threatened" in Maryland. Top right, her quarry.As shad swim upstream and over the top of the Conowingo Dam near Port Deposit, Md., they pass a plate glass window. In a booth on the other side of the pane, workers count the shad, which stream past by the dozens, even hundreds. When dams and overfishing depleted the shad population, a "fish lift," or water-filled elevator, was built to help the fish over the Conowingo Dam in the Susquehanna River.