August 08, 2011
By Dr. Hal Schramm
Recreational anglers' interest in catfish is surging, and fishery biologists are responding with stepped-up assessment and management plans focused on catfish. Fundamental to managing a population is knowledge of the spatial extent of the "manageable unit." For example, the effectiveness of a harvest regulation for a reach of a river would be diminished, if effective at all, if a catfish moved beyond that river reach or into another river.
Of the big three catfishes — blue, channel, and flathead — blue catfish, although the least studied, have been considered the most mobile. Tag and recapture studies have reported blue catfish swimming distances of several hundred miles or more to their recapture site; but these "gee whiz" reports, although authentic, do not necessarily reflect the norm. In the lower Mississippi River, average distance between tagging and recapture sites was 8 miles for blue catfish, 33 miles for channel catfish, and less than 1 mile for flathead catfish. It appears that blue catfish share their gypsy ways with channel catfish in the lower Mississippi River, but the movement distance estimates for both species should be considered underestimates. The movement distances were based on recaptures in the intensively electrofished study reaches, so any long-distance swimmers were not included in average movement calculations. Such are the vagaries of tag-recapture studies for estimating movement.
Although described as a main-channel, riverine fish, blue catfish thrive in reservoirs. In Kentucky Lake, a 184-mile long impoundment on the Tennessee River, 67 percent of tagged fish were recaptured an average of 15 miles upstream, 17 percent were recaptured an average of 11 miles downstream, and 16 percent were recaptured within a few miles of their tagging site. Most fish were recaptured during May to June, suggesting the predominantly upstream movement may have been associated with a spawning migration.
Biologists' knowledge of blue catfish movement took a giant step forward when catfish biologists, managers, and anglers assembled at St. Louis, Missouri in June, 2010 for the Second International Catfish Symposium, sponsored in part by In-Fisherman.
Tribute to Tributaries
Missouri Department of Conservation (MDC) Resource Scientist Zach Ford is using information from angler and biologist recaptures of tagged blue catfish to quantify movement in several tributaries to the lower Missouri River and pools 20 to 22 of the Mississippi River. Preliminary trends from this ongoing study indicate that blues in big rivers moved less than those in tributaries, and half of the recaptures in the Mississippi and Missouri were less than 6 miles from their tagging site. Blue catfish dispersal averaged 14 miles in Missouri River tributaries. The greatest dispersal was in the Platte River where fish were recaptured an average of 20 miles from their tagging site.
Complementing MDC's study, University of Missouri doctoral student Danny Garrett and U.S. Geological Survey fishery researcher Dr. Charlie Rabeni looked deeper into blue cat movement. Focusing on a 60-mile stretch of the lower Missouri River, they used radio and acoustic telemetry to monitor movement at weekly and biweekly intervals. Fish were collected in the Missouri River during prespawn, and the sampling ensured that the tagged fish were collected from throughout the entire 60-mile reach. Radio and acoustic telemetry allowed frequent detection of the uniquely coded fish, providing detailed information about movement among and within different habitats.
Missouri River blues were mobile, averaging 33 miles per year; annual distances traveled by individual fish ranged from a lazy 1 mile to an energetic 245 miles. Although fish differed in their movements, tracking revealed a general pattern of distinct periods of restricted movement separated by brief migrations. Movement was greatest during the Prespawn to Spawn Period, averaging 16 miles the first year and 21 miles the second year. Fish moved less during summer and fall, ranging from 6 to 12 miles, except for one vagabond that took a 137-mile swim. Average movement was only 1.5 miles when blue catfish occupied winter areas, primarily scour holes below wing dikes, in the Missouri River.
Missouri blue cats accomplished the three-part annual movement cycle of spawning migration, summer and fall home, and winter home in one of three ways. Thirty-five percent of the fish remained in the Missouri River, moved less than 6 miles throughout the annual cycle, and showed no evidence of a spawning migration. A second group of fish, 28 percent of the 29 blues tracked, migrated to and from seasonal habitats within the Missouri River. This group exhibited a spawning migration, but individual fish migrated at different times from March through June. A third group, 11 of 29 fish tracked (38 percent), migrated up tributaries to spawn, then returned to the Missouri River and moved little throughout the summer and fall.
Movement out of wintering holes began when the water was a chilly 46°F. Most of the spawning migrations occurred during May and June when water temperatures were 59°F to 68°F. Migration to the wintering holes occurred in the fall when water temperature was 50°F to 54°F and rapidly dropping.
Greatest movement occurred during the spring spawning migration when river flows were highest. Of course, this could just be coincidence — catfish spawn in the spring, rivers rise in the spring. But Garrett and Rabeni proposed that river discharge may trigger movement, noting that the proportion of blues that migrated to tributaries to spawn was greater in the year with greater May discharge. Moreover, two blue catfish moved into tributaries when flows increased but returned to the Missouri River to spawn when the high flows subsided, and movement increased during brief increases in flows throughout the year. Certainly more than two years of assessment are needed to tease out the effects of discharge on movement and, in particular, the use of tributaries for refuge or spawning.
Virginia Tech researchers Daniel Stich, Joseph Grist, and Brian Murphy used radio telemetry to uncover seasonal movement patterns of 5- to 41-pound adult blue catfish in Lake Norman, a 32,000 acre highland hydropower reservoir in western North Carolina.
Greatest movement occurred in the spring when minimum distance traveled averaged 3.2 miles. In May, half the radio-tagged fish migrated to a 3-mile-long reach in the upper part of the reservoir. The fish moved little during summer and winter, with minimum distance averaging less than 0.6 miles. Blues moved more in the fall, but minimum distance averaged only a little more than one mile throughout the season.
Paralleling the distances moved, blue catfish had the smallest home range in winter, averaging about 250 acres. Summer home range averaged a little more than 600 acres. Home range was greatest in fall, averaging 4,200 acres, and also the most variable, ranging from 47 to more than 10,000 acres.
Stich and crew went high-tech with their telemetry — the transmitters attached to the fish not only enabled them to pinpoint the catfish but also indicated water temperature "at the fish." Lowering the probe of an oxygen and temperature meter allowed the researchers to determine both the depth and the dissolved oxygen concentration at the location of the fish.
Depth occupied by the blue catfish averaged 43 feet in the winter, 20 feet in spring and summer, and 30 feet in the fall. Blues sought high dissolved oxygen concentrations. They were rarely located in water containing less than 6 parts per million (ppm) dissolved oxygen, and in the winter they were usually in water with oxygen concentrations greater than 8 ppm. In summer and fall, when mean oxygen concentrations in Lake Norman were below 6 ppm, blue catfish occupied water that was, on average, up to 4 ppm higher than the mean concentrations in the reservoir; and some fish were located in the highest dissolved oxygen concentrations measured anywhere in the lake.
The most exciting finding from the environment-at-the-fish measurements was temperature selection. From October through January, blues selected water that was a couple degrees cooler than the average lakewide temperature. The minimum lake temperature declined to 48°F in December and 45°F in January, and the minimum water temperature occupied by any catfish was the same as or a few degrees above the minimum lake temperature measured.
From May through August, the radio-tagged blues occupied water that was up to 12°F warmer than the average reservoir temperature. It is important to note that average summer water temperatures in this highland reservoir range from 68°F to 73°F, so it is not surprising that the blues might seek warmer water.
But there's more to this story. Throughout the year, environmental temperatures measured throughout the lake had a far greater range than the temperatures occupied by the fish. In other words, blue cats were selecting a relatively narrow range of temperatures from those available. In July and August, the range of temperatures they occupied — 77°F to 90°F — was the narrowest range of temperatures occupied during the summer. Warmer and cooler temperatures were available.
September marked the hinge point between blue cats seeking zones warmer than the lake average and seeking zones cooler than the lake average. All blue cats located in September were in water of 73° to 77°F even though much warmer and cooler water was available.
Several findings interest the angler side of my brain. First, I'm inclined to conclude that summertime blue cat anglers should confine their fishing to 77°F to 90°F water. In October and November, look for water temperatures between 59°F and 68°F, which might be the coldest water available. In January and February, look for 46° to 50°F. But consider that these temperature guidelines may differ from lake to lake.
Blue catfish appear to have different temperature preferences in the summer and winter. Although this requires further investigation, these are the first data I've seen that suggest fish may have seasonal temperature preferences.
Biologists have significantly advanced our understanding of blue catfish movement and provided some good guidance for managers in terms of the spatial scale of management. In short, any attempts to manage blue catfish — whether through habitat management, stocking, or regulations — should be thinking long reaches of river and river-tributary complexes.
The Missouri research emphasizes the importance of tributaries to blue catfish populations. It was clear that blues moved into the tributaries to spawn and then quickly vacated, living up to their reputation as large-river cats. Other tagged fish were content to spawn in the mainstem Missouri.
Why are tributaries important? The Missouri, like other large navigable rivers, is severely channelized and provides little habitat diversity. Hollow logs and similar structures needed by cavity-nesting blue catfish may be especially scarce. Tributaries can provide essential habitat diversity and should be managed to provide features that are not only important to their resident species but also to big-river fish, like blue catfish, that seek specific habitat characteristics that may not be available in the big river.
The Lake Norman study provides data that biologists can use to assess habitat suitability for blue catfish in reservoirs and possibly flowing-water systems. Certainly, additional studies of this rigor are needed to better quantify blue catfish habitat requirements. While biologists await such studies, any efforts to increase blue catfish in reservoirs where populations already exist would do well to assess the amount of water that meets the temperature and dissolved oxygen preferences of blue catfish, identified in Lake Norman.
What about stocking reservoirs where blue catfish don't exist? First, biologists need to determine whether this species can make a positive contribution to the fishery without adversely affecting it. Introduced blue catfish have drastically changed healthy and productive fisheries in Atlantic-coast states. However, if blue catfish benefit a fishery without negative consequences, such as reservoirs in Oklahoma and Texas, the Lake Norman information can be used to assess whether a reservoir has sufficient habitat preferred by blue catfish.
There are more than a few things for anglers to ponder. In large, navigable rivers like the Missouri, scour holes downstream of dikes provide the depth and shelter from current that blue cats seek in winter. Expect upstream movement from these areas in the spring when the water temperature rises above 46°F, but movement may not be far. Tributaries can be heavily used for spawning. Tributaries near wintering holes should be prime targets. Expect some spawners to move into the tributaries when the water temperature tops 60°F.
Whether blues remain in tributary rivers remains unknown. The fish tracked in the Missouri study were all tagged in the Missouri River during the Prespawn Period, so information about movement of tributary-resident fish was not available for comparison. However, MDC tagged blue catfish in tributary rivers during April through July, which indicated blue catfish remain in these smaller streams. Whether they are visitors or residents, don't expect areas where you catch blues during the spawn to be good summer and fall spots.
Blue catfish tend to move to the upper end of reservoirs during the spawn. While they show habitat fidelity and establish home ranges, these fish are highly mobile and home is a big piece of real estate. The temperature, dissolved oxygen, and depth preferences identified in Lake Norman provide food for serious thought about where to look for blues in the reservoirs you fish.
Will the time, temperature, dissolved oxygen, and depth specifics hold on your favorite water? Check it out. My guess is that the temperature and dissolved oxygen preferences apply to the species, not to a single population, and will be useful in your reservoir. The time when blue cats switch from preference for warm water to preference for cold water probably varies among reservoirs. Seasonal changes in depth preference may also be important, but temperature and dissolved oxygen preferences probably trump depth preference.
"Dr. Hal Schramm is a professor of fisheries at Mississippi State University, and a frequent contributor to In-Fisherman publications on science topics."