BETHEL — The number of large trout caught in the Upper Androscoggin River near Bethel has been on the decline in recent years and state biologists are trying to figure out why.

Maine Department of Inland Fisheries and Wildlife biologist Francis Brautigam met recently with about 30 fishing enthusiasts at the Bethel Inn to share observations and information, and to discuss river management for the future.

Brautigam noted that the overall quality of the river water is vastly improved over what it was decades ago. He cited the shutdown of the paper mill in Berlin, N.H., for improving the aesthetic appeal of the Androscoggin.

For more than a decade, the department has been regularly stocking the river with rainbow and brown trout. Biologists have been tracking the size of both stocked and wild fish.

From 2001 to 2009, the percentage of all trout 14 inches and longer declined.

Brautigam said there is some evidence that wild rainbow trout made up a higher percentage of the larger, older rainbows caught by fishermen.

He said reduced sizes of fish are likely attributable to more competition due to higher stocking rates, marginal summertime water temperatures, possible poaching, barriers such as poor-quality road culverts carrying small tributaries that limit fish mobility and a decline in organic material that had been generated by the upstream paper mill, which fed the creatures that the fish, in turn, fed on.

And, he said, the more fishermen on the river, the more the fish that are caught and released are handled. “It could make it tough for the fish,” he said. “I’m astounded at the use of the river.”

Brautigam also presented limited information showing that for the area 4½ miles south of Davis Park in Bethel, summer water temperatures for two years were sometimes higher than recommended for trout.

Trout need colder water, which has a higher oxygen content, than most other species of fish. The preferred temperature range for rainbow and brown trout, Brautigam said, is between 54 and 66 degrees Fahrenheit. The lethal level for brown trout is 80, and for rainbows, 77.

In 2008, he said, “river temperatures were outside of the preferred range, and on some occasions the daily maximums were close to lethal levels for rainbows.

“In 2003, over roughly the same time period, temperatures generally ranged outside the preferred range, and less than lethal limits, although sometimes water temperatures were in the preferred range,” he said.

Several fishermen at the meeting said they, too, have noticed a decrease in the size of the fish they have caught in recent years.

John Wight, who lives along the river south of Bethel, said he has noted summer water temperatures around 80 degrees, and refuses to take people fishing in those conditions for fear of further stressing the trout.

Another fisherman noted the recent Route 2 widening project in the Gilead area, where significant portions of the tree canopy that had previously shaded stretches of the river have been removed. The result, he said, could be additional warming of the river water as it passes through that area.

Brautigam was asked if it would be realistic to eliminate some of the competition for wild trout by ceasing to stock the river, or at least greatly reduce it.

He said the overall catch rates among fishermen would likely “plummet” in that scenario.

Brautigam said his department is in the early stages of developing a fish management plan for the river, and input from a wide range of anglers, fishing guides and fishing-related organizations is important. Over the coming winter he plans to form a citizen advisory group to help with a vision for the Upper Androscoggin, and to work on a management plan.

More on temperatures

After the meeting, Wight elaborated on his water temperature observations over the years.

“I take temperatures when I’m guiding,” he said, a practice he learned from his father, “who championed leaving the fish alone when the water was anywhere near 70.”

Wight said he believes there has been a “long and steady increase” in water temperatures here.

For the past four years, he has lived south of Bethel village. For one of those years the summertime temperature was 80, and for the other three years in the high 70s, he said.

And on guiding trips as far north as Errol, N.H., Wight said he has found temperatures in the mid- to high 70s. “It’s stressing them and causing a lot of fish mortality,” he said.

Wight has recently been researching water temperatures in other parts of the United States. In some locations, states monitor rivers and ban fishing for trout when the temperatures get too high. He found one river in Connecticut and others in the West that have such programs.

He thinks the time may have come for Maine to do the same.

“If they want to promote holdover fish in order for them to live two or three years, they need to protect them,” Wight said.