Pike and Walleyes Thermocline Patterns

Thermocline pattern pike and walleyesAs summer wanes, a stellar pattern solidifies on many lakes that produces big numbers of super-size walleyes and northern pike. Often overlooked by the masses, it provides steady action well into fall.  “Call it the squeeze play,” quips angling ace Scott Glorvigen. “When low levels of dissolved oxygen in deep water force cool-water forage into a narrow band higher in the column, big predators move in for the feast. Anglers able to capitalize on the conditions can enjoy some of the season’s finest fishing.”


In a nutshell, the pattern occurs when a lake stratifies by temperature. Cold water in the lower level, known as the hypolimnion, can become inhospitable to whitefish, tullibees, smelt and other baitfish when dissolved oxygen levels dip below critical levels. As a result, forage species are forced upward into the midsection, called the metalimnion. Home of the thermocline, this slice of paradise holds cool, oxygen-rich water.


While predators may suspend and harass baitfish wherever the metalimnion occurs, areas where this band of water contacts classic structure, such as reefs and humps, set the stage for epic feeding binges and great fishing.


“When my son Adam and I recently fished a walleye tournament on northern Minnesota’s lakes Winnibigosh and Cutfoot Sioux, the pattern was in full swing on a forage-rich bar surrounded by deeper water,” Glorvigen notes. “We caught walleyes up to 28 inches, plus numerous pike over 10 pounds, with a number in the high teens and two over 20 pounds.”


Finding The Zone

Not limited to Winnie and Cutfoot, the squeeze play is a factor on fisheries literally across the continent, although Glorvigen cautions that not all lakes stratify, and not all that stratify do so in a uniform manner. To complicate things a bit more, variations in the depth and thickness of the metalimnion are possible in different areas of the same body of water.


Still, finding the fish-attracting middle ground is often a simple task with high-quality sonar. Since a thin layer of suspended particles often rests on the dense upper reaches of the hypolimnion, the break between the two layers is often visible on sonar. Glorvigen leans on his Lowrance HDS electronics to reveal the thermal breakline. “If you don’t see it, adjust your sensitivity until a slight band appears,” he suggests. “You can also determine its location by noting the depth at which you stop marking fish.”

Rigging redtails and other beefy baitfish is deadly on 
walleyes from late summer through the fall turnover.


Suspended pike and walleyes shadowing wayward baitfish in open water can be challenging to locate. If you do spot a school surrounded by larger arcs, trolling deep-running crankbaits can be a lethal tactic.


Glorvigen prefers to focus on predators and prey interacting on structure, however. “My favorite spots are adjacent to deep basins,” he begins. “I often start on the south sides of such structures, where southerly, surface-warming breezes stack up the baitfish. It’s hard to go wrong targeting the 10 feet of water column just above the thermocline, which in northern lakes typically lies 25 to 30 feet beneath the surface.”


While cranks are a hit with suspended fish, the structure bite hinges on tethering beefy minnows to live-bait rigs. “Once you find a promising area, the idea is to mimic one of the struggling, cold-water baitfish predators are keying on,” he explains. His go-to setup consists of a 7-foot medium-action spinning outfit spooled with 10-pound-test superbraid such as steel-gray Northland Bionic Walleye Braid or Berkley FireLine Crystal, tipped with a 6- to 7-foot leader of Berkley Professional Grade Fluorocarbon in the 8- to 10-pound range. 


“Fluoro is abrasion-resistant enough to handle most pike, while the braid’s sensitivity is critical to monitoring the minnow’s behavior,” he explains. “When the minnow gets excited, you know a big predator is lurking in the neighborhood. Often, letting the minnow run on slack line will trigger a strike, and thin-diameter braid is also easier for the minnow to run with.”


Glorvigen typically rigs a 6- to 9-inch or larger creek chub or redtail chub on a size 1 or 2 upturned red hook. “Light lip-hooking keeps the bait lively and struggling,” he says, noting that at times, predators show a preference for baits hooked in the corner of the mouth. “I believe this allows the minnow to process more oxygen, which keeps it even more active,” he explains.


Another trick for keeping bait in top condition is tempering the minnows’ water before sending them into action. “Bait dealers keep them in tanks at 40 to 50 degrees,” he says. “If you put them in 75- to 80-degree lake water without getting them accustomed to it, they go into shock and die.” To avoid such frustrations, he buys minnows in an oxygen bag. At the dock, he places the sealed bag in the livewell and fills the well with lake water. “This slowly raises the minnows’ temperature, so getting dropped in the lake isn’t such a shock to their systems,” he says. Once the baitfish acclimate, he opens the bag and releases them into an aerated minnow bucket like Frabill’s AquaLife Bait Station, for safe keeping and easy retrieval.


“State and local regulations vary,” he says. “If you’re not allowed to transport lake water, make sure you bring water from home, or you’ll end up dumping your minnows on shore at the end of the day. And at $9 a dozen, that gets expensive.”


If cold fronts and light biters dictate a stinger hook, he adds a #12 to #16 treble near the dorsal fin, though he cautions that the extra steel may impede the minnow’s movements. “There are times a stinger is critical, and times it’s a deal-breaker, so you have to experiment,” he explains. Stinger or not, a ¾- to 1½-ounce egg sinker on the mainline provides ample ballast; a small bead separates the weight from the small swivel used to link braid with leader material.


In clear water, speeds of .7 to .8 mph get the nod. Dark water calls for a slower pace, to give predators time to find the bait. In either case, when a pike or walleye grabs the minnow, Glorvigen gives it room to run. “I keep my bail open and my trigger finger on the line, so it’s a simple matter to strip line off the spool,” he says. 


“Let the line coil on the surface and watch the coils,” he continues. “As soon as they start straightening out, raise your rodtip while reeling fast. When you feel the weight of the fish, set the hook.” Such maneuvers typically result in firm hookups without full-scale swallowing, which engender easy release and high survival rates. “If you have trouble reaching the rig through the fish’s mouth, simply slide a small forceps between the gills and pull the hook backward,” he notes. “It’s a lot easier on the fish.” 


Armed with such strategies, pike and walleyes are fair game until fall’s cooling water temperatures wash away the thermocline in late September or early October. Until then, however, the squeeze play is a deadly ploy for patterning supersize predators other anglers miss.