Every year, for a few nights in early autumn, the walleye action explodes on Northern lakes. It happens when maples turn red and harvest moons begin to glow. It’s then that walleyes start their autumn migration.
To be sure, late September’s walleye run is nothing like the mad-dashing spawning runs of spring; it’s a subtle migration that often goes unnoticed. In the North, anglers call it the “little run.”
The reason for this September migration is turnover — a term every walleye angler knows but few understand. In summer, Northern lakes are stratified with layers of water of varying temperatures. The warmest water lies near the surface and maintains its temperature down to depths of 25 feet. At that point, water temperature changes abruptly. This is where the thermocline begins.
The thermocline is a ribbon of cool water, up to 20 feet wide, sandwiched between the warm surface water and the icy water in the deepest part of the lake. During summer, warmwater species like bass are found above the thermocline, while cold-loving walleyes stay in the thermocline for all but a few hours each day. When summer anglers fail to find walleyes, they are usually fishing above the thermocline (where the water is too warm), or below the thermocline (where insufficient oxygen cannot sustain fish).
But as autumn approaches, a lake’s surface water quickly cools. Almost overnight, warmwater species like bass vanish. As the temperature difference between the surface water and thermocline shrinks, the thermocline recedes into an increasingly narrow band until it disappears completely. Icy water from the lake’s bottom then mixes with the warmer water above, until the lake’s temperature is uniform at every depth. When this occurs, the lake is said to have “turned over.” Walleyes then disperse throughout the lake, and finding them becomes a matter of luck.
September’s little run of walleyes takes place before turnover is complete. Cool nights and less daylight ignite an urge in walleyes to feed often and aggressively. This is especially true of large, solitary walleyes that have spent the summer in the thermocline. As the thermocline shrinks, these fish are squeezed into the shallows.
Locating the Thermocline
To fish early autumn’s migrating walleyes, you need to know if a lake’s shrinking thermocline still exists. Some sonar units can tell you this. Stop your boat over the deepest water you can find, and turn up the unit’s gain until fuzzy specks appear as a band across the middle of the screen. This image represents the start of a lake’s coldest and deepest water. The thermocline lies immediately above it.
You can also locate the thermocline by fastening a probe-tipped thermometer to ordinary kite string. Tie knots in the string at 1-foot intervals to measure water depth. By repeatedly lowering the probe and reading the thermometer, you’ll eventually reach a depth where the water temperature drops abruptly. This is the thermocline.
On the Move
Until the thermocline completely disappears sometime in October, walleyes will be traveling in water from 2 to 20 feet deep. Schools of walleyes will move from one patch of green weeds to the next in shallow water adjacent to sloping shorelines. The edges of stump-studded bays in reservoirs will also hold fish, especially if a nearby stream provides a current. Meanwhile, large, solitary walleyes prowl reefs and submerged spits that crest close enough to the surface to sustain green weeds.
In early autumn, it’s not unusual to spot walleyes in gin-clear lakes, lying among eelgrass and milfoil in less than 6 feet of water. You often see them at the ends of rocky points that practically divide a lake in two or in any sort of waterway that acts as a bottleneck. However, these fish already feel unprotected in direct sunlight, and they instantlyy scatter at the sight of a boat.
But during the little run, even big walleyes lose all wariness after sunset. Any narrow waterway will act as a funnel through which these prowling fish must pass. Where short bridges span the narrow places in lakes, the weedy channels under those bridges will always turn up walleyes on late September and early October evenings. The same is true of narrow waterways between islands and headlands.
What to Use
Fishing these narrow places at night with a slip-bobber rig is the surest way of catching fish. This rig consists of a hook, split shot, and a lighted slip bobber through which your line is threaded. A bobber stop small enough to pass through your rod’s line guides but large enough to prevent the bobber from sliding up your line is required. Some anglers use a small bead for a stop, but a piece of string tied in a knot around your monofilament is handier. For bait, hook a 3-inch shiner or fathead minnow through the lips with a circle hook; pinch a piece of split shot 10 inches above that. Remove a small piece of the bait’s tail; this will force the minnow to be more active in order to maintain its balance.
When the rig hits the water, the split shot pulls the monofilament through the bobber until the bobber hits the stop. The stop can be set for any depth by sliding the knotted string up or down your monofilament. Later, when you reel in, the stop will pass through your rod’s line guides, while the bobber slides down the line until it hits the split shot. The light vanishes when the bobber goes down, signaling a strike.