September 23, 2020
By Cory Schmidt
Biologists tend to view a fishery a little differently than anglers. A guide the likes of Ryan Gnagy adheres to his primary mission: to track reservoir catfish movements each and every day in order to keep his clients on the bite. While the guide’s sole purpose is to locate and catch fish, a biologist needs hard data and wants to understand the factors affecting a fish’s location. A biologist might discount the guide’s observations as “anecdotal.” They’re required to adhere to a systematic scientific method to accomplish the same goal—to locate fish and track their movements.
Relative to scientific tracking studies, less is probably known about the migratory tendencies of catfish than any other group of popular freshwater sportfish. Within the ictalurids, few tracking studies have followed blue catfish for extended periods. That changed recently when researchers at Kansas State University (KSU) and Kansas Cooperative Fish and Wildlife Research (KCFWRU) unit revealed intriguing results from what was likely the most ambitious blue cat tracking study to date.**
About Milford Reservoir
Until the early 1990s, Kansas’ largest lake, 15,700-acre Milford Reservoir, had been known for kicking out 20-pound-class channel catfish. The fishery took a turn in the early 1990s when the Kansas Department of Wildlife, Parks and Tourism (DWPT) began stocking Milford with thousands of blue catfish. Given the productive nature of the Republican River reservoir, including ample spawning habitat, rocky structure, and a healthy population of gizzard shad, Milford’s blues prospered, grew, and multiplied. As often happens when blue cats enter a system dominated with native channel cats, blues largely displaced them. In 2013, Stephanie Stanley caught a lake record 82.05-pound blue, a fish that remains the lake record today.
As the fishery bloomed with new year-classes of blue catfish, anglers flocked to the lake, catching and harvesting big numbers of fish. Finally, recognizing a need to protect the lake’s spawning stock, as well as to sustain its biggest specimens, Kansas biologists enacted special regulations starting in 2018. Daily harvest of blue cats was reduced to five fish, including only one catfish over 40 inches. A slot limit protects blues between 25 and 40 inches.
Milford, perhaps the most popular fishing lake in Kansas, offers a bounty of angling opportunities. Beyond blue, flathead, and channel catfish, the lake’s rich food base sustains a healthy population of wipers, white bass, walleye, crappie, largemouth, smallmouth, and spotted bass. Impounded and filled in 1967, Milford provides drinking water and flood control for Kansas residents. Known for dramatic variations in flow—from flood stage to localized drought—the Republican River has over the years swept huge volumes of silt into the lake, creating vast featureless flats over which schools of shad and catfish roam. Milford’s shoreline is dominated by limestone cobble and boulders; the lake averages 22 feet with a maximum depth of 65 feet near the dam.
In 2012 and 2013, KSU graduate students Kayla Gerber and Zachary Peterson with project supervisor Dr. Martha Mather of the KCFWRU, placed acoustic tags in 123 blue catfish and tracked them with 20 stationary receivers placed throughout the reservoir, as well by manual tracking at 57 locations distributed throughout the lake. Catfish were tracked 24 hours a day from June through November, yielding the most comprehensive set of blue cat tracking data ever assembled. Most of the tagged catfish measured between 16 and 24 inches—all mature adults—with some smaller and larger individuals up to about 43 inches. The tracking results revealed that small and large fish did not exhibit significantly different movement patterns.
Included in the study were factors such as flow velocity, as well as water temperature and dissolved oxygen throughout the water column, measured at each receiver site. Kansas DWPT also estimated numbers of gizzard shad at each site via electrofishing, as well as the abundance of chironomid larvae. Diets of Milford blue cats were analyzed using gastric lavage—a harmless method of extracting stomach contents with pressurized water. Three major prey categories dominated the diets. Gizzard shad were most abundant in larger catfish, while zebra mussels and chironomid larvae provided sustenance for smaller blues. Shad and chironomids were most abundant in the upper reaches of the reservoir.
One fascinating study result showed how Secchi disk depth (water clarity) readings at each site affected catfish location. Tracking data showed a strong correlation between catfish location and low Secchi depths (low water clarity). In Milford, the researchers made a solid connection between low Secchi depths and high concentrations of phytoplankton (chlorophyll). They further surmised that although catfish and shad locations didn’t always overlap, catfish may in fact have tracked prey via high chlorophyll concentrations, which coincided with low Secchi depth clarity. The catfishes’ intent, the biologists hypothesized, was to hone in on plankton-grazing shad, which would ultimately lead them to their preferred preyfish (i.e. catfish tracking the prey of their prey). Further, catfish avoided areas with dissolved oxygen below 4 ppm.
For the tracking study, Milford Reservoir was divided into five similar sized regions based on receiver location—upper, upper middle, Madison Creek, lower middle, and lower (near dam) reservoir areas. From June to November, blue catfish were consistently clustered (aggregated) in the upper middle region. Specifically, for all months and both study years, more fish pinged the receivers in the upper middle reservoir “funnel” area. This region starts just above the upper reservoir constriction zone and ends just below the Madison Creek confluence. Noteworthy was that although fish were consistently concentrated in this funnel, they were not sedentary and frequently moved to other locations before returning to the funnel location.
Throughout the study period, blue catfish were not common in the six northern-most sites of the upper reservoir, nor in the lower section near the dam, even in fall (October-November). Although some tagged fish moved south to the deepest part of the reservoir near the dam in fall, others moved just south of their summer location in the middle section of the reservoir. Another group of fish remained in their summer location near the confluence of Madison Creek through November.
In general, the study revealed three types of catfish aggregations: 1) fish that used the upper middle reservoir funnel in summer, then visited a range of southern (near dam) locations in fall; 2) fish that used the upper middle funnel in summer and fall and did not move south; 3) fish that used the Madison Creek region throughout the study months without exhibiting a fall deep-water migration.
By far, the most significant aggregation occurred at the funnel just below Madison Creek’s confluence, which corresponded with higher flow velocity. A second major group stationed on the west side of the lake at the lower end of the Madison Creek constriction zone. Finally, perhaps not surprisingly, many more fish were detected using areas close to the main river channel.
No Milford blue cats appeared to move out of the reservoir system, either via the upstream Republican River or downstream through the dam. Previous studies have apparently shown that stocked fish occasionally move out of the reservoir, while naturally reproduced fish may not. The biologists surmised this may have indicated that ample spawning habitat exists within the reservoir itself.
Relative to incoming water flow and catfish movement, one would generally expect greater fish migrations during periods of heavy flow or high water. The biologists note that the lack of upstream movement might have been a direct response to the low water, localized drought conditions present during the study period. As we’ll note soon, anglers who fished the lake during the high-water 2019 season experienced a completely different pattern.
A Guide’s Prespawn Perspectives
While the study lacks tracking data during the late winter through Prespawn Period, Guide Ryan Gnagy of Prime Time Catfishing, offers his observations of the reservoir’s blue cats during this period. He says that although the data don’t reflect an upstream movement of blue cats, he commonly finds concentrations of shallow fish in April and May. He finds that male catfish largely disappear from his catches in mid-May, as they begin nest building, with the main spawn phase occurring in mid-June.
“Spring catfish location on Milford is highly variable,” he says. “Last year, we had ridiculously high water. All this water flooded shallow flats up in the Republican River—areas that are normally high and dry. When this happens, blues push up onto these flats, in as shallow as a foot of water, to feed on invertebrates and baitfish that use the newly inundated brush and grass.
“Other years, when flows are lower or more consistent, you might find prespawn blues in 3 to 7 feet of water,” he says. “Some Aprils, we’ve had our best fishing out in 35 feet of water, and it’s not always just a factor of high versus low water. You’ve got to spend time looking at electronics to first find areas with the highest concentrations of bait. On Milford and most other lakes, the biggest clouds of bait always have some catfish nearby. You also can’t get locked into one specific depth range, because shad can be highly migratory.”
Gnagy calls the lake a “big silted-in mud bowl,” with most of the best fishing occurring on the flats. “I know the tracking data show that fish pass through the upper middle narrows and pinch area,” he says, “but I don’t think the fish necessarily hold there. When feeding, catfish are up on the flats adjacent to the main channel. But in spring, they can be anywhere, including flats or ledges right off the bank.”
During the Prespawn Period, Gnagy and other topnotch anglers such as John Jamison and Justin Cook anchor and fancast rigs all around their position. For Gnagy, that means ditching a physical anchor and hitting the spot-lock button on his trolling motor control. Six to eight rigs are cast around the boat to intercept active catfish.
“Spot-locking is so much more efficient than a traditional anchor,” Gnagy says. “Even in a stiff Kansas wind, if you’ve got a powerful trolling motor, you’ll hold right on the money. Typically, we’ll spot-lock in a single location for 20 to 30 minutes before moving. But if we’re on fish, we’ve stayed locked on a single spot for up to 7 hours.
Jamison, who’s fished Milford for many years back to the days when the lake produced trophy channel cats, helped pioneer an original fancasting approach. “This same shallow-water pattern exists on a lot of good blue cat lakes, including Lake of the Ozarks and Truman,” says the legendary catman and winner of numerous national tournaments. “I use Humminbird side-imaging to pinpoint key structural areas, such as a 1- to 3-foot rock ledge. But these days, we’re targeting specific big fish that appear on the screen as white slashes. Ideally, we want multiple fish on the screen before we drop a waypoint and anchor.”
Once anchored, he deploys three rods off either side of the boat, each placed in a Driftmaster rod holder on the stern of his Lund Pro Guide. “During the earliest phases of spring with water temps in the mid- to upper 40s and increasing with warm days and spring rains, there’s a ton of fish in the backs of the creeks,” he says. “A lot of days, we anchor just off the bank in 3 feet of water. But a cold front can also make fish slide back out into 10 to 17 feet pretty fast.” The peak bite usually occurs when water temp reaches the low 50s in spring, he says.
“On Milford, we fish up near the main river on the north end. Pay attention to any current. If they’re pulling water or the lake is dropping or rising, we get into necked-down areas with a little more water movement.”
Justin Cook, who along with partner Gary Ryan won the March 2019 Cabela’s King Kat USA tournament on Milford, uses similar springtime tactics. “We fished a Cabela’s event there 15 years ago and caught big channel cats,” Cook says. “Now, we sort through lots of slot-sized blues to get one kicker fish over 40 inches, and the rest below the 25-inch slot.
“At the 2019 Cabela’s tournament, we fished below the (Wakefield) causeway—a small pinch area with high water flow—that’s always got catfish moving through. We also fished a small feeder creek on the upper west side of the lake.”
Cook focused on small humps, little 1 to 2 foot rises in the lake floor, as anchor positions. “These little humps cause fish to pause as they travel up and down the lake or across shallow flats. Usually, these are harder bottom areas that might have some rock or mussels on them.” Thanks to a 53-pound blue, Cook and Ryan—one of the top teams on the King Kat Circuit—weighed a total of 98.64 pounds in the one-day event. In 2020, the King Kat trail returns to Milford for tournaments on March 28 and the 2020 King Kat Classic on October 30 and 31.
Beyond increases in fishing pressure and the frequency of catfish tournaments, Jamison and Cook have observed another trend. “The sport is growing in popularity in all phases,” Jamison says. “Including recreational and tournament anglers, and trotliners. All over the country, and certainly at Milford, we’re seeing a big uptick in trotlines. These folks take a lot of fish for community and family fish fries. But we also know a lot of these fish—including big ones—are sold to restaurants by folks who don’t have a commercial license. So, it’s a concern.
“These days, Milford’s special regulations have shifted the population to the point we’ve got a ton of fish in the 25- to 40-inch slot, those 7- to 15-pound-class blues. What tends to happen with a reg like this, I think, is anglers and trotliners end up keeping every fish over 40 inches they catch. So, time will tell if the regulations ultimately produce numbers of big fish. For now, if you want to go catch and release a bunch of 7- to 20-pound blues, Milford is a good bet. The lake gets a lot of pressure, but on a good day you can catch 25 fish or more, including lots in the 35- to 39-inch range.”
Cook believes the lake produced more big fish five to eight years ago than it does today. “Milford was becoming a top-notch trophy blue fishery,” he says. “But as the trotlines have expanded, you’re not seeing as many big fish. No question, numbers of fish are through the roof, but it’s more of a catch-and-release fishery for midsize catfish, which isn’t a bad thing at all.”
Anglers report similar trends with increases in trotlines almost everywhere, and catfish populations evolving in response to new regulations. Certainly, we favor the protection of mature, spawning-size catfish, while also maintaining a tradition of harvesting smaller specimens. Given the rarity of truly giant blues and the time it takes to grow them, however, one wonders whether it’s wise to harvest even a single leviathan.
*In-Fisherman Field Editor Cory Schmidt often writes about the catfishing scene, from the latest hot fisheries to science and conservation. Contact: Guide Ryan Gnagy, Prime Time Catfishing, 785/250-5709.
**Mather, M., K. Gerber, Z. Peterson. 2015. Assessing distribution and movement of blue catfish In Kansas reservoirs. Final Report to Kansas Wildlife, Parks, and Tourism.