ISLE ROYALE, Mich. (AP) _ An orange-tinged, full moon rises above the dark line of trees along the shore as the 14-foot motorboat hums quietly across the still waters of Rock Harbor.

Biologist Joseph Kaplan stands in front, gripping a powerful spotlight with one hand and a pair of binoculars with the other. He and partner Keren Tischler, who is piloting the boat, are seeking a family of common loons known to nest on Caribou Island, part of the Lake Superior archipelago that forms Isle Royale National Park.

Their midnight mission: Capture a 6-week-old chick, pluck a few feathers and draw a blood sample, which will be tested for mercury contamination. It's part of a broader study of the extent to which the poisonous element has tainted the island chain's ecosystem.

To the casual observer, Isle Royale might seem the last place where industrial pollution would be a problem.

The 45-mile-long island chain is a federally designated wilderness area, undeveloped except for a scattering of houses, camping and boating facilities and the park headquarters. Its lakes teem with fish. Moose sightings are common on its forest trails, and nighttime silence occasionally is broken by a gray wolf's ghostly howl.

But in the 1970s, researchers who tested Isle Royale's inland lakes were shocked by the levels of toxic PCBs they found _ in some cases, 30 times higher than in surrounding Lake Superior.

Conclusion: It must have traveled through the atmosphere.

``It shows how much of a global problem airborne contamination is,'' says Jack Oelfke, a National Park Service resource management specialist. ``You can't just point your finger at the local smokestack any more.''

Since then, elevated mercury levels have been found on and around Isle Royale. While some probably came naturally from bedrock, atmospheric contamination is the primary culprit, Oelfke says.

With a $45,000 grant from Canon U.S.A., a team of scientists is conducting a two-year investigation. In addition to the water itself, they're studying sediments from lake bottoms, rain and snow, microscopic plankton, fish (northern pike and yellow perch), deer mice and moose.

And they're looking at loons _ web-footed birds with a plaintive, high-pitched cry. Expert divers, they often stay beneath the surface as long as a minute hunting for fish.

Their dietary choice makes loons a good indicator whether mercury is progressing up the food chain. Recently hatched chicks are especially useful because they've eaten only in one area, while adults _ which migrate to the Gulf Coast for winter _ have foraged elsewhere.

Another reason loons were picked for the study is their tendency to return to the same area each spring, enabling scientists to monitor them over the years. Some live as long as 30 years.

``They're not very shy. Many times they'll swim right up and look at us in our canoes,'' says Tischler. She and Kaplan are loon specialists for BioDiversity Inc., a nonprofit ecological research group based in Freeport, Maine. They've taken samples from 19 Isle Royale loons in 1998.

Of course, the first step is finding them, which on this night isn't easy. For more than an hour the biologists fruitlessly search the chilly, clear water around Caribou Island, the family's established territory.

They visit the former nesting site, a pile of sticks partially concealed beneath an uprooted white spruce a few feet from the water. Here, the parents took turns guarding their egg during the 28-day incubation period. They abandoned the nest after the chick was hatched.

Tischler frequently cuts the boat motor and Kaplan plays a cassette recording of a loon's quavering wail. Sometimes the serenade will draw a live response. Tonight, no takers.

Finally, while moving the spotlight in a sweeping arc across the middle of the harbor, Kaplan sees them floating placidly on the water surface.

Mom and Dad flee as the boat approaches, but curious Junior swims toward the light. At one point he turns away, but the scientists make soft hooting noises that keep him coming.

As the boat draws alongside, the chick suddenly dives. But Kaplan swoops a long-handled net below the surface and hauls the struggling loon aboard. Tischler wraps him in a towel and cradles him on her lap. He soon calms down but for the occasional, muted howl.

The beak is long and sharp, the eyes brownish, the back feathers slate gray. The head is darker, while the underside and throat are white. When he reaches adulthood, white feathers will encircle his neck like a collar.

The biologists work quickly, not wishing to panic the parents, which observe the scene from a prudent 100 yards.

Kaplan affixes identification bands to both legs. He inserts a tiny needle into one of the thin, rubbery legs and draws blood into a syringe, then cleans the spot with an alcohol-soaked gauze.

They take a half-dozen feathers from the chick's downy breast and shoulder and place them in a plastic bag.

The bird is getting restless, kicking and whining more frequently, as the biologists pour some of the blood sample into a solution to prevent it from coagulating, which would render it useless for mercury detection. The rest will be archived for future study of loons, a threatened species in Michigan, which is believed to have 300-500 pairs.

After weighing the chick _ a healthy 5 1/2 pounds _ the biologists are ready to free him. They approach the nervous adults with caution, not wanting to scare them away. About 30 yards from the closer one, Tischler puts the youngster overboard.

Hesitantly at first, the family reunites.

``They're good parents, stayed right there,'' Kaplan says. ``This was pretty stress-free. Some birds can get very excited.''

The chick, and others the biologists studied in 1998, should yield useful information for the mercury project. Its blood sample will be compared with those from loons nesting around Sargent Lake, one of the most heavily contaminated of Isle Royale's inland waters.

One loon chick from an inland lake sampled in 1997 had mercury levels six times higher than those of loons a few miles away in Lake Superior.

Oelfke, the project director, hopes to release an analysis of findings from all the field studies next summer. In addition to documenting the extent of mercury contamination and its effects, the report may shed light on where it's coming from.

One possible source is industrial emissions from Thunder Bay, Ontario, 35 miles north. But there is evidence that at least some of the mercury had more distant origins.

For example, inland lake water samples have turned up traces of a herbicide commonly sprayed on Great Plains cornfields. Scientists believe the poison may have been blown into the upper atmosphere and traveled hundreds of miles before settling.

If so, atmospheric mercury may have done likewise, Oelfke says. There's even speculation that some Isle Royale mercury drifted from as far away as China, whose factories belch huge amounts.

``It's important to document what's going on,'' Oelfke says. ``If we're having these kinds of problems on this remote island, what's happening elsewhere?''