May 13, 2021
By Matt Straw
Snow on the trout opener is something to celebrate. Not only does it sideline fair-weather fishermen, its presence is a clue to savvy anglers. Snow on the banks means cold water in the stream, and water temperature is a powerful predictor for determining where trout concentrate in winter.
Generally, in these conditions, it's in "frog water"—areas with slow current, flat terrain and wide pools where current spreads out and slows further—that tends to be ignored by anglers. Of course, if it has been consistently warm, trout will be in their usual spring hangouts.
Several telemetry studies have proved that stream-dwelling browns often winter where trout can't even survive in summer, then migrate miles between winter and summer habitat. Timing those migrations during spring, and especially on the trout opener, depends on weather and water temperature.
David Clapp and Dr. Richard Clark of the Michigan Department of Natural Resources (DNR) put radio tags in eight brown trout between 17 and 25 inches long and followed them around the Au Sable River for 365 days. Lee Meyers of the Wisconsin DNR implanted 22 browns with transmitters in Beaver Creek and tracked them for two years. Ross Langhurst, also with the Wisconsin DNR, tracked browns in the Oconto River, one of the state's longest trout fisheries.
While these biologists tracked browns year-round, our focus here is on spring, when the most essential tool for locating large concentrations of trout isn't a lure, bait or fly, but rather a temperature gauge for measuring the water temp.
Below 50° F
Typically, brown trout move upstream from summer habitat to spawn in smaller tributaries during fall, then make long migrations down to cold-water haunts.
"Some trout moved 40 miles downstream after spawning [during fall] in the South Branch of the Oconto to winter in the main branch," Langhurst says.
Wintering sites were described as dish-shaped pools with no overhead cover. Winter pools aren't necessarily deep, but they tend to be in areas of low or level gradient, where the water isn't running downhill. Often, these areas offer marginal summer habitat, holding no trout at all after the wildflowers bloom. On the opener, anglers tend to overlook connecting waterways that get too warm in summer, but odds are high that that's where most browns will be when the water is still cold.
Brown trout sometimes run out of the rivers they use in summer and fall to larger, slower rivers, and they might even retreat to ponds, lakes or reservoirs. Once browns establish themselves in winter pools, they stay put.
"When the stream iced up, we could walk right over tagged trout," Meyers says. "They didn't move."
Clapp and Clark observed no upstream or downstream movements once browns nestled into wintering pools. And in all these studies, browns didn't leave wintering pools until the water warmed above 50 degrees, no matter when that was.
"For the first two weeks of the season, browns are way downstream," Langhurst says. "Almost all tag returns came from downstream segments of the study range."
Cold river temperatures push browns into the aforementioned "frog water." In the Beaver Creek study, browns left the branches and main stem of the river to winter in the Peshtigo River, which offers nominal habitat in summer.
"All the tagged browns remained in a two-mile stretch of the Peshtigo during winter," Meyers says. "Winter sites were midstream, where the depth averaged 2.4 feet. Active fish were always midstream."
Look for relatively shallow, dark-bottomed areas with no boulders, logs or other obstructions. Gravel is key. Search areas where trout streams empty into rivers that never hold trout in summer. You might find thousands of trout and no competition.
When water is cold and their metabolism is slow, big trout hold in one spot longer and tend to feed on smaller items. A large minnow might take days to digest. Browns key on smaller forage like fish eggs, caddis larvae and mayfly nymphs. During the early part of a cold spring, present beads, flies, jigs or bare hooks tipped with a waxworm or live nymph.
50° F TO 60° F
Some browns begin to migrate upstream when water temps hit the high 40s. From that point to about 52 degrees, early browns move slowly, perhaps only migrating from one pool to the next over the course of days. They continue to prefer slow water, but tolerate quicker flows for short periods.
Meyers notes that initial upstream movements of his tagged fish began as temperatures reached 50 degrees. But, most browns waited until temps hit 55. Some didn't budge until the Peshtigo reached 64. This means marginal-water honey holes sometimes conceal lightly-pressured browns until June.
"When the water temperature topped 60 degrees for the first time, all browns were moving," Meyers says. "But not all fish started out at the same time. Some started as water eked into the 50-degree range, some later. The overall migration period lasted 1 1/2 months. The entire month of May was a migration period."
When water temperatures reach 50 degrees, look for large pods of trout staging in the lower end of the trout streams they inhabit all summer, in slow, deep pools. Migrating trout pause longest when they encounter barriers, which aren't always overwhelming obstacles like dams or waterfalls. Barriers include cascades, rapids, riffles and long stretches of clear, shallow water—anything that encourages rest or instills trepidation. The largest concentrations of browns are directly below barriers when water temperatures range from 50 to above 60.
During migrations in moderate water temperatures, spinners rule. Covering water with a spinner saves time. Make one short, one medium and one long cast from each standing position. Then take three steps upstream and start over. Cast slightly downstream to tighten the line, and let the current sweep the lure along without reeling until the spinner is directly downstream. Try not to wade if you can avoid it, but if you need to in order to hit the far bank, fish the water you intend to wade through first. Size No. 0 and No. 1 blades stay up on small streams, while No. 2 to No. 4 blades tend to match flows in larger streams.
Above 60° F
Movements from winter to summer habitat ranged from 4.5 to about 22 miles among all tagged fish. Clapp and Clark note that once summer habitation is achieved, browns hold in a territory for 4 or 5 days before leaving to stake out a new one. After repeating that pattern 2 or 3 times, they circle back and start over.
But atypical weather alters that behavior. In recent years, weather patterns skipped spring and went right from winter to summer. If water warms too fast, browns make another migration.
"In the high-60-degree range, browns relocated upstream to cooler, spring-fed tributaries," Langhurst says. "By the time water temperatures reached 70 degrees, they were gone."
If the opposite happens, browns can move back downstream. Three years ago, some streams in Minnesota registered 60 degrees on June 1 and 55 on June 28. In the Beaver Creek study, Meyers noted that a drop in stream temperature during spring or summer drew browns downstream, well below normal summer habitat—sometimes all the way back to areas that, in normal years, would warm enough to be lethal for trout.
If the temperature gauge reads 70 degrees, patrol small water upstream—cooler headwaters, deep shade, inflowing springs and areas of intensified ground flow. But if temperatures drop back into the 50-degree range, work your way back downstream.
The Au Sable study revealed that browns over 17 inches feed primarily on fish—minnows, suckers and small trout—especially in warmer water. But huge browns can be caught on tiny flies during a hatch, when insects are so abundant all trout have to do is hold in a current lane and open their mouths. Abundance is the key. If enough rainbows or other species are spawning, goliath browns might feed exclusively on eggs for a time. But, in water over 60 degrees, big browns rely heavily on stealth and surprise tactics at night, when smaller trout can't see them coming.
Cast an Original Floating Rapala and let it drift on the surface. Twitching it now and again will produce the occasional heart-stopping explosion out there in the dark. Big, white deer-hair flies that float high—like a Wulff, Bomber or Mouse—are exciting offerings at night, too.
Nocturnal browns often feed in water they never use during the day—shallow, featureless flats that are way too open and exposed in sunlight. Don't waste time and equipment fishing snags and logjams at night. Get to the river before sundown, stake out a nice, boring flat with an even bottom and—if fly casting—pick out openings in the brush for safe backcasts.
Anglers often choose spring areas and tactics based on a great outing years ago. They go back every opener and experience mixed results. But spring browns go through stages. Understand both the locations and tactics they prefer during each stage, then choose tackle and tactics to match. And pray for snow.
Note: This article was featured in the Midwest edition of April's Game & Fish Magazine.