The Secret Lives of Reservoir Blue Catfish

The Secret Lives of Reservoir Blue Catfish

Reservoir-Blue-Catfish-Lead-In-FishermanA number of studies using biotelemetry over the past decade have significantly improved scientific knowledge about the seasonal and daily movements of the monsters that haunt the dreams of many trophy catfish anglers. The findings reveal trends in reservoir blue catfish behavior that give anglers a glimpse into the lives of blue catfish and help them unravel the mysteries of their quarry.

Vanishing Blues Of Texoma

Corey Lee, fishery biologist on Lake Okeechobee in Florida, did his master's degree research at the University of Oklahoma at Lake Texoma on the Texas-Oklahoma border, tracking movements of blue catfish tagged with ultrasonic transmitters. His study explained the lament among local anglers that blue cats disappear in the summer.

Lee and his co-workers caught and tagged 30- to 70-pound blue catfish from the three segments of Lake Texoma: the Red River arm, the Washita River arm, and the main lake at the junction of the two arms. Long-term monitoring of the tagged fish led to surprising results. In late April to early May, most of the blue catfish from the three sections of the 89,000-acre reservoir began a migration that by June moved them miles up the Red River.

"It surprised me," Lee says. "Most tagged fish didn't stay in the lake during the summer, even though there's plenty of habitat there and a huge population of forage fish. They for the most part abandoned the lake during the summer and moved up the Red River. Some of them moved a long way upriver. Two fish tagged in the main lake moved 25 miles upriver within a couple months of when we tagged them."

Lee was prepared to study the movements of catfish within the lake, so the wholesale movement upriver into the relatively shallow Red River made detailed monitoring of the fish difficult. Fortunately, he had positioned stationary receivers in the channels of the Red and Washita rivers to document if any tagged fish moved out of his study area. Those receivers proved that when Texoma's blue catfish travel, they travel fast.

The stationary receivers identify individual tagged fish and their depth as they move up- or downstream past the receiver. The receivers cycle back and forth between recording fish identity and depth roughly every 15 to 20 seconds. Lee's tagged blue cats often moved past the receivers so quickly that only one of the two measurements were completed before the fish moved out of radio range.

Locations of blue catfish #38 in Lake Texoma, beginning at its tagging location on December 15. Some fish such as #38 moved long distances through the spawning season and throughout summer. Fifty blue cats were tagged in Lee's study. Click to enlarge.

"They weren't wandering, they were booking upstream when they went past those stationary receivers," he says. "It was like they knew where they were going and weren't wasting any time getting there." He was puzzled why most catfish ignored the Washita River and moved up the Red.

"The Red and Washita watersheds are close to each other and had nearly identical rainfall and water levels, but virtually no fish in our study migrated up the Washita," he says. "Some of the fish we tagged in the Washita arm moved down into the main lake, up into the Red River arm, and eventually up the Red River. I have no idea why they showed such preference for the Red. There is definitely something about the Red River, maybe something in its water chemistry, that makes blue cats prefer it over the Washita."

Most of the tagged catfish that migrated as much as 25 miles up the Red River in late spring moved back down into the lake in late September and early October. The fall migration seemed to correlate with late season rain events that temporarily raised the river's level. "It was like they were riding pulses of high water back down into the lake," he says. "Once they were back in the lake, they returned to much of the same places where we tagged them."

While some blue cats were wanderers that moved around the lake's arms and main basin during the winter, others were largely sedentary. Those homebodies stayed in relatively small, deep-water home territories throughout winter, with occasional forays to shallower water, often after dark.

"We did 24-hour tracking on three of the stationary fish," he says. "We checked them every few hours, and at one point, around 2 or 3 in the morning, a 54-pounder was gone from where he'd been all day and evening. We searched and found him around a bend, under a school of shad. He moved back and forth under that school of shad for an hour or so, then bee-lined back to almost exactly where he'd been."

Lee's suggestions to anglers based on his findings: "Don't waste time trying to catch blue cats from the main lake in summer," he says. "There are always a few of them scattered around the lake and two arms throughout the year, but most of the fish in our study went up the Red River. In winter, though, they're back in the lake in all their favorite spots. They seem to set up on the shelves along the old river channel, and relate to points, bends, and drop-offs along the channel. When they move, they move to where shad are, so we assume they're feeding. If you find shad in the winter, you're probably going to find multiple blue cats that have moved to that area and are actively feeding."

Wheeler tailrace homebodies

Wheeler Dam, operated by the Tennessee Valley Authority, impounds the Tennessee River to create Wheeler Lake in northern Alabama. While at Auburn University, Ryan Hunter, who's now with the State Parks Division of Texas Parks and Wildlife, radio-tagged blue catfish in the Wheeler Dam tailrace, which feeds Wilson Lake, and tracked their movements.

"It was like there were two groups of fish in the tailrace," Hunter says. "Some moved a lot during the year, some rarely moved. The two groups were distinct in their movements. For a while, we were concerned a couple of them were dead, so we did 24-hour monitoring. We found those fish would stay in the same spot for hours, then all of a sudden move directly to the base of the dam, move around for a while, probably feeding, then move directly back to almost the same spot where they started."

Other catfish in Hunter's study were more mobile. A significant number moved from the two-mile long tailrace below Wheeler Dam into the calmer waters of the upper end of Lake Wilson. One blue cat apparently migrated through Lake Wilson's lock-and-dam system into Pickwick Lake. About 1,700 catfish also received dangler tags (non-telemetry tags) over several years to track harvest and movements, and one of those fish was eventually caught by an angler in the Mississippi River 620 miles away.

"Our model showed that water temperature was the most important variable affecting movement," Hunter says. "Cold water didn't inhibit movement. In fact, they were more mobile in the winter than in the summer. Moon phase also had an effect on movement—catfish were more mobile on darker nights. Moon phase, however, didn't affect movement as much as water temperature."

Norman's Fussy Eaters

Stomach contents (percentage by weight) of blue catfish from Lake Norman based on Grist's research. The most common food items (Asiatic clams, clupeids, and Chara) are shown. Chara is a plant-like alga also known as stonewort and muskgrass. Other foods eaten in low quantities not shown here include crayfish, aquatic insects, and miscellaneous items and unidentifiable fish.

Joe Grist, fishery biologist with Virginia's Marine Resources Commission, radio-tagged and tracked blue catfish on North Carolina's Lake Norman as part of his graduate studies at Virginia Tech. He found that movement in Lake Norman differed substantially by season, with the strongest and quickest migration occurring during prespawn.

He tracked blue cats from all over the 32,750-acre lake as they made a relatively quick and nearly universal prespawn migration to a 3.1-mile-stretch of the upper lake. The speed at which the fish migrated and the concentration of tagged fish in the relatively small area was impressive.

"When we went into one little cove in that part of the lake, our gear was pinging like crazy from all the tagged catfish that were in there," Grist says. "That surprised some of the local guides. They said they'd fished that area hard during the spawn and only caught a few fish. I don't know if blue cats don't feed much during the spawn, or if there are other reasons, but the anglers didn't do well catching them even though we found a lot of fish in a relatively small area during the spawn."

After the spawn, the catfish dispersed throughout the lake, revealing a surprisingly high level of fidelity to specific locations where they were originally tagged. Grist's tracking of fish during summer echoed other studies—some blue cats were so sedentary that the researchers were concerned the fish were dead. But 24-hour tracking proved the fish did move, often after dark, to specific locations where they apparently fed before returning to within feet of their starting point. "In the summer they'd consistently move into a cove, or from cove to cove, around 9 or 10 p.m., apparently to feed, but they were always back home by the time the sun came up," he says.

Stomach sampling as part of Grist's research revealed major changes in the diet of Lake Norman's blue cats from summer to winter. "In the spring and summer, there were fewer fish in the diets of large blue catfish," he says. "Their diet was dominated by clams in the summer. We'd handle fish and they were lumpy, full of clams, just about any time during the summer. In the fall they started feeding on fish, and by winter they were almost exclusively feeding on gizzard and threadfin shad." Perhaps shad become more sluggish in cold water and are more vulnerable to predation, while clams and mussels are an easy meal in summer.

Changes in diet—from stationary clams to roving shad—may explain differences in movement among blue cats at Lake Norman. They were more mobile in winter than in summer, feeding on schools of shad during the day. "I talked to scuba divers who work for Duke Power (an electric power company), and they said that in winter, it wasn't uncommon for them to be working at the bottom and to have the light go dim," Grist says. "When they looked up, there would be a big school of huge blue catfish blocking the sun as they cruised overhead. It was like a wolf pack of blue cats on the hunt for schools of shad."

That pack behavior reflected what Grist saw in his radio-tracking surveys. While his tagged fish were widely dispersed around Lake Norman during the winter, they were often concentrated in discrete areas. "We thought most of the catfish would be concentrated in a few locations where there were lots of forage fish, but it was like there were small concentrations of blue cats dispersed all over the lake," he says.

Grist was impressed with the speed at which blue cats made seasonal migrations. "They were quick," he says. "They weren't searching for where to spawn, or where to spend the summer or winter. They knew where they were going and went directly from point A to point B. Individual fish moved dozens of miles in five days or less once they decided to move. How they were able to accurately find their way to such specific locations isn't known."

Blue catfish remain a fascinating and mysterious member of the catfish family. Anglers who use the growing pool of scientific information to decipher when, where, and how to target blues can up their odds of success.

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