Trout are cold-water fish, requiring cooler, more highly oxygenated water than warm-water species like bass. That's why, in summer, stocked trout in lakes go deep, sometimes suspending below the thermocline. It's also one reason why trout move shallow in winter.
Sunfishes and other panfish use shallow flats all summer, while trout inhabit mid-depth and deeper flats. In winter, the process reverses. As ice begins to form, hordes of panfish charge down the drop-offs like a plague of locusts. They set up deep where they begin gobbling benthic organisms. Trout simply relocate in the recently abandoned shallows, where the departed panfish left plenty of shallow invertebrates.
Few freshwater fish—only the various salmonids, the trouts, and whitefishes—can plow right into current at temperatures of 33°F and retain the temerity to bite. Temperatures under the ice are warmest deep (38°F to 40°F), but remain a constant 32.5°F to 35°F on shallow flats 2 to 6 feet deep. Those are uncomfortable environs for bass and panfish, but not for trout.
Active rainbows, browns, cutthroats, and brookies under the ice classically use the biggest flats available in the 4- to 8-foot range, especially where those flats are adjacent to sharp drops into deep water. They come in to forage on minnows, small crayfish, aquatic worms, mayfly nymphs that burrow in the sand, and other invertebrates.
Less active fish drop deeper, classically using 20- to 30-foot flats, or suspending over even deeper water. Where flats gradually taper into deeper water, trout scatter more. Where the route from shallow to deep is more distinct, trout seem to occupy shallow-water concentration points.
Trout, however, tend to suspend, perhaps rising to within 6 feet of the ice and swimming parallel to it right into the shallows. In lakes without key shallow flats, trout alternately suspend to feed on minnows and hug bottom to feed on nematodes, blood worms, and such. Finding areas of softer bottom in a predominantly rocky lake can be key. Active trout move up on shallow flats or suspend early and late in the day on clear days. The bite is extended on dark, snowy, cloudy days.
Try to determine where trout might move up onto the flat by studying a lake map and drilling a few holes. Trout tend to migrate deep-to-shallow on inside bends in bottom contours, or where deep water makes the closest approach to the shallow flat. Structure may have less influence over where trout travel, but areas of structural diversity may hold the most trout. The winter flats pattern, however, is all about bottom-type diversity. Different bottom types hold different organisms, offering more foraging options within a smaller area.
Migrating trout are not necessarily the most active. They seem to need time to acclimate to the colder, brighter shallows. They need to find a few things, get a few scraps under their belts, before they really turn on. This isn't to say that the first trout to reach the flat won't swim right up and snarf the first bait it sees, because it might.
Be on the ice early to drill holes, well before light. Or again at mid-day, well before the trout show up in the evening. Trout are spooky. You're standing four or five feet above them. Shuffle your feet, knock over the bucket, play touch football with empty beer cans, and the bite may not happen, at least nowhere near you.
Drill early, set up portable shelters to keep light from streaming down the hole, and get everything ready for silent operation before setting baits. Set a chair or bucket just the right distance from the hole. Leave some snow under your feet. Put everything essential—baits, tackle, extra gear, thermos and food—within easy reach.
Get comfortable, because moving around is bad news. Don't even make the bucket creak against the ice. Turn off the depthfinder. At this depth, it doesn't help. Trout come zipping in from nowhere, anyway, and sonar makes noise trout can hear and feel. (Sometimes, however, it may actually attract unpressured trout.)
Give 'em what they eat. Trout can be selective, picky eaters under the ice, or they can be Tasmanian devils, devouring the first thing they find. Generally, the best bait is a live nymph because it's something trout commonly forage on and something they rarely refuse when it's presented correctly. Maggots, which imitate caddis and other aquatic larvae, waxworms, redworms (if you can find any), and small crappie minnows also make excellent baits.
Most trout lakes in the North Country tend to be clear, and trout can be extremely line shy. Use thin, pliable, 1- to 4-pound monofilament line in a color that matches the background. Use smoke or gray shades in clear water, green lines in green water or near weedlines, and brown lines in brown water or against bluffs. In cover or where trout over 5 pounds are common, nudge up to 6-pound test.
To present small livebaits, use a bobber. Tiny cork or balsa floats are best, something oval or pencil shaped that slips under easily. Slip the float on the line and peg it lightly, so it can be pulled while fighting a fish. Or use a slip float and bobber stop. Suspend the bait 8 inches to three feet off bottom. (In states where two rods are permitted, place baits at different depths. In states where only one rod is allowed, coordinate depth experiments with your partners.)
Lively baits are best, and it doesn't pay to continue switching baits. Maggots, worms, and waxworms need frequent changing, so reserve them for hot bites. A properly hooked nymph stays alive and breathing with its feathery gills for hours, as do small minnows.
Tiny #12 and #14 trebles, #12 to #8 single hooks, and jigs weighing 1/100-ounce or less are key. Experiment with gold or "jeweled" trebles, but most days on most waters, a plain bronze hook and no weight works best. If weight is needed, use one tiny dust shot for nymphs, maybe a single BB for minnows. Hook a nymph once lightly under the carapace behind the head, and bring the point back out at the next segment break along the back. On a minnow, slip the hook point under the skin along the dorsal fin.
Active jigging with light pointy plastic tails, tiny plastic grubs, or genuine ice flies is an option. Dull natural shades are best. Use light line in the 1- to 2-pound range, with tiny horizontal jigheads in the 1/120- to 1/80-ounce range. These drop slowly—perfect for shallow water. Get them to bottom, pause, then lift them all the way to the hole in a gentle, subtle series of twitch hops, imitating a nymph rising from bottom.
For ultraspooky trout, stay away from the hole altogether. Use light tip-up rigging or a Slammer, position a small lively minnow or nymph a foot or two off bottom, and refill the hole with snow, or cover it with a piece of dark cloth. Stand at least 25 feet away, perhaps jigging in slightly deeper water within the travel zone.
Some stocked and natural trout lakes may not have extensive shallow shelves. In that case, explore the shallowest flats near the sharpest break into deep water. Browns, cutthroats, rainbows, and brookies use bluff banks when they have to, but they prefer to roam the flats—where most of the insect life is likely found.
Softer bottom areas have more food, so search for substrates ranging from sand to silt. Deeper fish can be triggered with more active techniques with vertical spoons like Swedish Pimples, search lures (spoons with tiny jigs, maggots or nymphs suspended beneath on a mono leader), or horizontal jigs like the Turner Jones Micro series. Trout can be anywhere in the water column, so begin working the jig right under the hole.
Trout are active biters in cold water, but can be exceptionally wary, especially native trout and trophy specimens. Trout have an excellent sense of smell, so cover your scent on line and lure with something like Dr. Juice or Kastaway's Kodiak salmon-oil scents. Trout have excellent vision and lateral-line senses, too. For consistent success, think shallow, think natural, think simple, and think stealth.