Maine’s lakes and streams are the “last true stronghold” for brook trout in the eastern United States with more healthy populations than the other 16 states combined, according to a report released this week.

But the report also cautions that Maine’s wild brook trout are under increasing pressure – particularly from Bangor to the south and east – from the effects of urbanization and the introduction of non-native fish species.

In the first comprehensive study of its kind, the group Trout Unlimited teamed up with state and federal agencies, other conservation organizations, and researchers at two Virginia universities to evaluate brook trout populations in more than 11,000 East Coast subwatersheds. The report defined subwatersheds as varying in size, but typically containing 25 to 75 miles of streams.

The overall results are alarming for the “brookie,” a fish beloved by anglers and regarded by scientists as an indicator species of an ecosystem’s environmental health.

The researchers found nonexistent or greatly diminished populations in nearly half of all subwatersheds, severe population fragmentation, and a total absence of wild, self-reproducing trout in the vast majority of large rivers in the East.

“The assessment data tells a somber story of brook trout decline across their range, but the data also offers hope for restoration and recovery in many areas,” states the report, titled “Eastern Brook Trout: Status and Threats.”

Strong and healthy brookie populations do exist, the authors added, but they are rare – that is, except in Maine.

More than 330 subwatersheds evaluated in Maine were “intact,” meaning that wild brook trout inhabit at least 90 percent of their historical habitat in that area. By comparison, the other 16 states combined had 142 intact subwatersheds, bolstered largely by New Hampshire and Vermont.

Maine also was singled out as the only state to have extensive, intact brook trout populations in lakes and ponds. The vast majority of the intact lake and pond populations were found in northern and western Maine.

The one caveat in the report was that the study did not have population data for 64 percent of Maine’s rivers and streams. But the authors said brook trout are known to exist in most of those waterways.

“Maine is probably in the best shape of every state up and down the East Coast,” said Gary Berti, Trout Unlimited’s Eastern brook trout campaign coordinator, who is based in West Virginia. “There is such a large area where they are in good shape.”

Forrest Bonney, the brook trout specialist for the Maine Department of Inland Fisheries and Wildlife, said in a statement that the state is working to protect wild brook trout populations through restrictive regulations, habitat conservation, and restoration of impaired streams.

“Our collective challenge is to protect our remaining brook trout habitat and restore populations wherever possible,” Bonney said.

While Maine’s trout populations may be healthy compared to those of other states, they are not out of danger, the report’s authors said.

Rapid development in southern and coastal Maine further threaten already shaky populations, while “poor land management” and dams have degraded habitat up through Bangor. Logging operations in northern Maine create roads and culverts that can lead to additional sedimentation.

Brook trout in nearly one-quarter of the lakes and ponds studied in Maine also were suffering from impacts of non-native fish species such as smallmouth bass, perch and muskellunge, which can outcompete the trout for food.

The full report, as well as maps and state-specific data, is available online at http://www.brookie.org