In one traditional method of lake-trout fishing, an angler holds in his or her hand a weighted line while trolling from a boat. To collect the line, the angler uses a jerry-rigged Victrola record player with a spool in the middle.

“As they pulled in the line, they turned on their [hand-cranked] Victrola,” said Joe Hackett, a fishing guide from Ray Brook. “Lake-trout fishing is so specialized. That’s something you learn from your father, or uncle, or grandfather.”

While fishermen still use weighted lines, Victrolas are less commonly employed. But lake-trout fishing still requires special skills and gear. These large fish spend the summer in the cold water toward the bottom of ponds and lakes, limiting the effectiveness of anglers with ordinary gear. The fish’s preference for cold water makes it vulnerable to climate change, according to a recent report by the Adirondack Nature Conservancy.

“Lake Trout and Climate Change in the Adirondacks,” written by Mary Thill, warns that warming trends and an increase in storm-water runoff could lead to a loss of lake-trout habitat in Adirondack lakes.

“Lake trout require the most demanding combination of temperature and oxygen of all New York’s freshwater game fish,” writes Thill, a conservancy employee who based the report on scientific literature and interviews with experts.

Lake trout are a cold-water species that requires water with a relatively high oxygen content and a temperature below fifty-five degrees Fahrenheit. With a few exceptions, the region’s native lake trout are restricted to waters north of the forty-third parallel (roughly, the Adirondack Park’s southern boundary) in lakes and ponds deeper than thirty feet.

Lake trout have already been extirpated from seventy-five lakes and ponds in the Adirondacks where they were once reported. Thill’s research indicates that degradation of habitat caused by storm-water runoff, acid rain, DDT, and fertilizers led to the elimination of lake trout from some waters. Overfishing more than a century ago also played a role, as did the introduction of invasive species. Thill says lake trout were eliminated from some lakes that were reclaimed for brook trout.

The fish still dwell in about 102 waters, according to the report. About half of these contain self-sustaining populations, while about three dozen are stocked with fish spawned from wild eggs collected in Raquette Lake. Lake trout are faltering in some waters, while their status is unknown in others.

Overall, Adirondack lake trout seem to be recovering from past environmental menaces, including acid rain, DDT, and pollution from septic systems. However, climate change poses a new threat: rising temperatures could lead to low concentrations of oxygen in the cold waters where lake trout live.

From spring into the fall, lakes have warm water near the surface and colder water toward the bottom. Typically, the deeper, colder water is well oxygenated, but the amount of oxygen is limited in the warmer months, which is when the oxygen is used by bacteria that decompose organic matter.

The oxygen gets replenished in late fall after the surface water cools, becomes denser, and sinks. The water remains mixed until the following spring, when it settles into layers again. If climate change continues to lengthen summers and shorten winters, as expected, the deeper regions of lakes are expected to have less oxygen in the summer and fall than they do now. Smaller, shallower lakes are thought to be the most vulnerable.

“It depends on the lake, but a lot of these darker lakes with organic matter in them will have oxygen depletion in the summertime,” said Dan Josephson, a Cornell University fisheries researcher based in Old Forge. “[This can] lead to a situation where you have no preferred habitat.”

Josephson said the loss of lake trout could have a big impact on an aquatic ecosystem. In many waters, lake trout are an apex predator, feeding on smaller fish such as suckers, minnows, and smelt. In the absence of lake trout, the populations of the prey fish could grow, and this might diminish the number of brook trout, which compete for the same food. Moreover, smelt eat zooplankton that feed on algae, so more smelt could lead to more algae blooms. The loss of lake trout may not be felt as keenly in lakes where other large predators dwell, such as invasive pike and bass.

Research by Josephson has found that Upper Ausable Lake, which is forty-nine feet deep, has had critically low numbers of adult lake trout and a dearth of younger fish. Ampersand Lake, which is equally deep, is another small lake suffering from low oxygen levels in its deep-water habitat, the conservancy report says.

Oxygen levels can also be reduced by algae blooms that are caused by storm-water runoff carrying fertilizers into lakes, which can be a problem on lakes with developed shorelines. Algae blooms use up oxygen when they decompose. After an algae bloom dies, it sinks to the bottom of the lake, where the bacteria continue to use up oxygen.

Upper Saranac Lake is one example of a lake plagued by an excess of phosphorus and nitrogen and algae blooms as a result of runoff, according to the conservancy report. The lake once contained a self-sustaining lake trout population that was used to stock other Adirondack waters, but that is no longer the case. The lake’s north basin has “de-oxygenated entirely,” the report says, while the south basin’s oxygen has been diminished. Scientists speculate that these changes have forced lake trout to seek out shallow waters where the smaller ones are preyed on by invasive warm-water fish such as smallmouth bass and northern pike introduced in the early twentieth century.

Rob Fiorentino, an aquatic biologist with the state Department of Environmental Conservation, said Upper Saranac is a lake where a number of factors have come together to harm the lake-trout population. “As you keep piling these stressors on, sooner or later bad things will start to happen,” he said.

And it appears things will only get worse for lake trout in vulnerable lakes. Data from the U.S. Historical Climatology Network show that the mean annual air temperature rose 2.1 degrees Fahrenheit in the eastern Adirondacks between 1976 and 2005, according to Thill’s report. It is projected to rise six to eleven degrees more this century. In addition, extremely heavy rains are occurring more frequently now than in the early 1900s, according to the climatology network.

In addition to reducing habitat, higher water temperatures could also affect the timing of lake-trout spawning in the fall. Scientists believe spawning is triggered when the water temperature falls below 55 degrees Fahrenheit.

With the help of DEC and Cornell University, the Nature Conservancy has begun to evaluate the long-term viability of the 102 lake-trout waters in the Adirondacks. The lakes will be ranked based on their physical characteristics, such as depth and volume, as well as by cultural and land-use variables, such as shoreline vegetation. The data will be provided to fisheries managers for private and public waters.

Mike Carr, executive director of the Adirondack Nature Conservancy, said his organization was motivated to study lake trout because the group has protected numerous lakes that contain them, including Follensby Pond near Tupper Lake.

“There’s been a tremendous amount of work done on brook trout over the years, but not so much on lake trout, and we’re starting to ask questions about what happens to a species that is so dependent on a very specific habitat—cold, deep, highly oxygenated water—in the face of climate change,” he said. “When you look to the literature, there isn’t much in the way of research out there. There’s been some important research done in 1977, but not much since then.”

The 1977 report was a management plan for DEC prepared by aquatic biologist Daniel Plosila. Carr said he hopes that Thill’s report inspires additional research on the Adirondack native.

The conservancy is in the midst of a study about the population dynamics of lake trout in Follensby Pond. The research is being led by McGill University with help from Cornell and former and current DEC employees.

Follensby Pond is known to harbor big lake trout. In 1922, an angler caught a state record thirty-one-pounder in Follensby. That state record remained until a fisherman pulled a thirty-two-pounder from Lake Placid in 1986. Longtime Follensby Park caretaker Tom Lake told Thill that the average lake trout from Follensby weighs six pounds, a healthy size for the Adirondacks.

The conservancy report suggests that Follensby could be a refuge for lake trout in the face of climate change. For one thing, it’s very deep (up to 102 feet). For another, because of its bathtub shape, it has little shallow water (thus limiting habitat for invasive fish like bass). Finally, researchers found in September 2013 that Follensby has ample supplies of oxygen at depths between thirty-six and eighty-two feet.

“It’s been called an old-growth lake-trout fishery,” Carr said. “It’s very, very special. It may be one of the most special lakes in the United States for this reason.”

There is some concern that if the conservancy sells Follensby to the state, the lake will be vulnerable to overfishing. It has been expected that the conservancy will sell Follensby to the state, but Carr said he is focused now on finishing a multi-year deal to sell sixty-nine thousand acres to the state, nearly all of it timberlands once owned by Finch, Pruyn & Company.

Joe Hackett, the fishing guide, said if Follensby were open to the public, it would receive a lot of action from anglers. Lake trout rank fourth in popularity among anglers in DEC’s Region 5, which makes up the majority of the Adirondack Park. Hackett thinks special regulations should be imposed to protect the lake trout from being depleted. “My recommendation is to make it catch and release only and closed in the fall,” Hackett said.

Thill said fishing management, which is only touched on in her report, will be addressed in detail in the lake-trout study led by McGill University.

Above, State biologists Rob Fiorentino, left, and Jim Pinheiro inspect a lake trout on Lake Placid for signs of age after weighing and measuring it during a 2013 survey (photo by Mary Thill); and below, Follensby Pond (by Carl Heilman II).

This story originally appeared in the Adirondack Explorer, a nonprofit newsmagazine devoted to the protection and enjoyment of the Adirondack Park. Get a full print or digital subscription here.