By the time spring has come and gone, flatheads have transformed from a phase of almost complete inactivity to becoming metabolic superheroes. The changeover isn’t as quick as Clark Kent in a phone booth; it happens with environmental conditions shifting through the season at nature’s pace. Still, there’s a lot happening in a relatively short time, making this the most unsettled season for flatheads. It also starts out slow and often frustrating for anglers, but ends with some of the best fishing of the year.

Flatheads pass through several phases from late winter through the Spring Coldwater Period on to Prespawn. During early phases in particular, they almost seemingly disappear before showing up for a good prespawn bite. But along the way, they’re just living the life, responding to environmental cues that push their biological buttons for survival and reproduction. Along with that are physiological and behavioral responses that dictate where they are, what they’re doing, how aggressively they’re feeding, and where they’re going. Sounds simple enough. Know what cues them and make predictions about location and presentation.

But even the best fishery science available and our catfishing experiences don’t give us a formula that tells us all there is to know. There are just too many variables and processes happening. And, no two rivers are exactly alike. Even in a single water, conditions can be quite different from one spring to the next.

But what we do know today is making early-season flatheading more like a fair game of hide and seek than a magic act. Discoveries from scientific studies and experiences of top anglers are developing into something like an unfinished roadmap, but with no single road showing a guaranteed connection between you and flathead town, though one route in particular—water temperature—looks like a good one to follow.

Cold-Blooded Control

Temperature is a life-controlling factor for cold-blooded animals like the flathead catfish. Temperature regulates metabolism—physiological processes—and affects behavior such as activity and feeding. Metabolism slows in cold water and speeds up in warm water. Temperature alone doesn’t tell us everything about what flatheads are doing, but it offers some basic clues to various stages of behavior that flatheads cycle through during the early season.

To follow the thought process through, step back to winter, when flatheads are experiencing the coldest water of the year. In more northerly areas of their range, flatheads congregate in wintering sites. These spots tend to be deeper holes, although they’re not always the deepest holes in a river stretch. Good holes feature rough bottoms with larger rocks or wood, which serve to reduce flow near bottom and provide current refuge for cold cats. In a long river stretch with several dozen possible wintering spots, there might be only a few holes that have the features to attract the bulk of the population.

This was the case in a Minnesota DNR study on the Minnesota River. Biologists sampling flatheads from river pools in December reported that flatheads wintered in select holes. Some of the sampled fish had sediment deposits on their dorsal surfaces, suggesting that they remained still enough on bottom for silt to settle on them. In a different tagging study in the St. Joseph River in Michigan, flatheads also didn’t move while they were at wintering sites. Whether the overwintering-hole scenario plays out in far southern waters isn’t known, but another tracking study showed it to be the case in rivers as far south as Missouri.

Getting back to temperature, it’s believed that flatheads at the coldest winter temperatures can become so inactive they enter a state of torpor or quiescence, to the point where they might stop feeding for long periods. Anglers fishing mid-winter congregations of flatheads Up North hook them on snagging gear, but flatheads rarely seem to bite traditional presentations then. We’ve had good success fishing for them in winter aggregates during late fall and early winter, when water temperatures are in the mid-40F range; but their interest in feeding seems to bottom out in water down to the low 40s and 30s.

A recent study provides a direct comparison of food consumption by flatheads across a range of temperatures in a controlled laboratory experiment. Dr. Jason Vokoun of the University of Connecticut, along with biologists Sam Bourret, John Hoxmeier, and Kevin Stauffer of the Minnesota DNR, presented preliminary findings of their research on coldwater feeding patterns, metabolism, and homing ability.

Over a 2-week period, flatheads were acclimated to 6 different temperatures ranging from 37F to 73F, fed rations of minnows, and consumption determined over another 2-week period. Consumption at 73F was higher than at the other temperatures. Flatheads rarely ate below 59F, most stopped feeding at 52F, and nothing was consumed at 45F or below. Metabolism, which was determined by placing flatheads in a respirometer and measuring oxygen consumption of the test fish in a resting state, also slowed at 59F and below.

Another aspect of their study included a field experiment in which they sampled flatheads from wintering holes and inserted transmitters. One group of fish was released at the wintering hole, while a second was transported almost a mile downstream and released there. All the fish released downstream moved back to the wintering site within 48 hours and remained there until spring. “It’s impressive that flatheads can ‘wake up’ in cold water and physiologically perform,” Vokoun says. “We were surprised at the ability of the fish to swim and move against current at low temperatures.”

Whether the results of the laboratory experiment, which used smaller flatheads, translates to larger flatheads in a natural environment isn’t known. Angling observations show that feeding slows considerably, possibly even stopping in the coldest water, but it’s hard to say that flatheads completely shut down in water less then 52F in the wild. On several occasions, In-Fisherman editors have caught flatheads from wintering sites on lures, suggesting that the fish at least can be prodded into striking at temperatures down into the lower 40F range—another case of how flatheads can “wake up” and perform in cold water.

Anglers fishing the earliest part of the Spring Coldwater Period might still find concentrations of flatheads in and around wintering holes, with conditions becoming more favorable for catching fish when water rises into the mid- to upper 40F range. In-Fisherman Editor In Chief Doug Stange: “We know anglers catch flatheads when they’re still in winter aggregates, using heavy leadhead jigs and plastics; but I don’t know if there’s increased catchability on lures compared to natural baits early. I’ve caught them under these conditions on cutbait, and if you sit on a hole, they’re catchable and cutbait’s an option.”

Siltbacks Astir

Warming water during the Spring Coldwater Period eventually cues flatheads to vacate wintering holes. The move seems to begin when water temperatures reach the upper 40F to 50F range, typically in early to mid-April in northern regions of the flathead’s range and early to mid-March in the lower Midwest.

Vokoun tracked flatheads in Missouri for his doctoral research. He found that all flatheads tagged in the Grand River, a tributary of the Missouri, moved to the Missouri to overwinter, while of those tagged in the Cuivre River, a Mississippi tributary, some overwintered in the tributary while others moved to the Mississippi. Proximity to favorable wintering spots was the likely explanation for how far flatheads moved.

When water temperatures rose above 50F in mid-March, flatheads began to move from overwintering areas and migrated toward river reaches used during the Prespawn and Spawn periods (mid-April to mid-July). The average distances during springtime were 39 miles in the Grand River and 14 miles in the Cuivre River, and the general trend was upstream movement.

Dr. Trent Sutton and Dan Daugherty tracked flatheads on the St. Joseph River in Michigan and found similar results; flatheads remained inactive in winter habitats, and when water temperatures reached 50F in early spring, all fish began returning to their summer locations. In the St. Joseph River, the spring migration period was shortlived, occurring over a two-week period, while in Vokoun’s study, the migration took longer for some individuals because spawning sites were farther from wintering areas. In both studies, many flatheads exhibited site fidelity, returning to the same general areas in which they were caught and tagged the previous year.

Vokoun says that cold fronts stalled the spring migration. “Migrating flatheads moving up into a tributary typically started to stage in April, working up the lower ends of tribs. Then when a cold front hit, they’d turn around and zip back downstream. Often they didn’t go all the way back to their original wintering hole, but found another hole they used temporarily. Once spring broke, they eventually went on with their migrations, and fishing started to pick up with the spring floods.”

Finding and catching flatheads during the spring transition can be hit or miss, but research offers some clues as to where they might be found during this phase. Vokoun says that migrating flatheads held at resting spots along their route. But the habitats they chose usually weren’t the heavy-cover types of spots they typically use later in the Prespawn and Spawn periods. “The sites where I located them were more characteristic of hydraulic breaks than heavy cover,” Vokoun says. “These spots were around topographic features that provided areas out of the main current. I often found them around clay points, which are a common feature in the rivers I studied. But overall, they weren’t as selective as they were in the Prespawn and Spawn periods about they types of features they sought.”

Stange: “In spring, there’s this whole grand transition with flatheads, moving from wintering areas, becoming more active, and bouncing from place to place. There’s potential for catching fish. In rivers that have fewer structural features, like points that act as current breaks, snags and instream holes are probably good spots to contact resting flatheads. Wing dams are probably used as resting spots for flatheads moving a long way in bigger channelized rivers, as are submerged logpiles.

“Earlier I mentioned that cutbait might be a good option early in the season. I haven’t experimented enough with cutbait in spring to say it works better—it might be a bigger part of the whole early-season story than we realize. I’ve seen anglers fishing down on the Red River in Texas, catching flatheads in colder water in March. They fished a deeper creek with reduced current off the main river. The fish either were in the creek since winter or moved up the creek from the river. They targeted big shallow snags and fished with cutbait.

“In February, or maybe it was March—I can’t recall, but the water was cold—I fished with catfish guide Jim Moyer on the Cumberland River in Tennessee. We caught flatheads on cutbait, those fish coming from a mid-depth area where the deeper channel transitioned onto an upstream flat. Flatheads might have been moving up through that funnel area and feeding on the flat.”

I like Stange’s thoughts on the value of cutbait early on. It’s a more subtle presentation compared to live baitfish, and might be more attractive to a cold-water flathead that’s not energetically pumped up to overtake a big lively baitfish. Cutbait also probably emits more scent and flavor into the water than a livebait, and it’s probably just as important in cold water to rebait with fresh cutbait often.

Darrel Carter from Elk Point, South Dakota, fishes U.S. C.A.T.S. tournaments and used to think flatheads didn’t feed in water under 50F. Then he started fishing a U.S. C.A.T.S. tournament on the Ohio River held in late February or early March each year. “The last six years I’ve fished that event the water was always 43F to 47F,” Carter says. “Every year I caught at least one flathead from deeper water on cutbait and saw other ones weighed in.

“Back home, I fish the Big Sioux and Missouri rivers. I start early in the year fishing cutbait in the main channel of the Missouri and catch flatheads, often when I’m targeting channel cats. In April, I catch flatheads and channels on cutbait in the lower 2 miles of the Big Sioux where it flows into the Missouri. By prespawn, I’m fishing about 10 miles up the Sioux, catching about a 50:50 ratio of flatheads and channels on cutbait around snags.”

Staying on top of early flatheads is an exercise in tracking water conditions and weather events. A water thermometer might be your best tool to decipher the changing patterns of the season. Early on when it’s cold, focus on areas around known wintering holes. If you don’t make contact, flatheads are probably on the move, so go to plan B and start covering water, fishing current breaks where migrating flatheads might stop to rest.

The water’s still on the cold side, so it’s probably best to sit on a spot a bit longer than you would in the latter part of the Prespawn Period. If a flathead’s there it’ll probably take advantage of the opportunity to feed because it’s expending a lot of energy to get to where it’s going. In the meantime, a feeding fish might pass through while your bait’s down there working. Another strategy is to set up in an area that looks like it serves as a funnel for traveling flatheads. It might be a constricted channel, or the slack side of a current seam, or something that looks like it gives you a better shot at fish moving through.

If a cold front drops the water temperature, go back to spots that have characteristics of a good wintering hole. When warming weather stirs things up, it’s probably time to go back to plan B and search for moving and resting fish or wait it out at funnel areas.

By mid-May and into June Up North, and from April into May farther South, with water temperatures breaching 60F, flatheads are settling into river reaches where they’ll eventually spawn, although settled is a relative term compared to the migration stint of the Spring Coldwater Period. They’re still moving, hopscotching among spots like big snags and rockpiles, to feed and scout out spawning areas. But metabolism’s ramped up, flatheads are feeding heavily, and the fishing’s as good as it gets.