Blue Catfish, Baitfish and Mussels

I've tried baiting with mussels on the Tennessee River. I've used fresh mussels and even scooped up some of the soured ones during a mussel die-off and used those," says Phil King, catfish guide and tournament pro from Corinth, Mississippi. "But I can't recall catching a blue catfish on them. In fact, I don't think I ever got a bite on them.

"The commercial fishermen used to bait with mussel meat so it must work. I knew a longtime catfish angler who used to fish with mussel shells. He removed the shells from the stomach of a catfish he caught, drilled a hole in each shell, and threaded a single shell on a hook.

"Sometimes the blue cats are eating so many mussels that their lips look like they're bleeding," King says. "When you get 4 to 5 miles below a dam on the river, the diet's almost all mussels. You can feel the shells in their stomach. I caught a 35-pounder that had a bellyful."

King observes a seasonal cycle to blues feeding on the bivalves. "In spring the primary food source is fish. As the water warms to the upper 40ºF range, the blues become tied to mussel beds and their diet's almost exclusively mussels. Sometimes the blues are so full of them that it can be difficult to catch a fish, even on shad. Almost every summer there's a mussel die-off. The shells open and the meat floats to the surface, making an easy meal for blues. This past June the mussel kill was the worst I've seen, and the blues were in better shape than ever."

Nearly every successful blue cat angler we know, such as King, fishes with baitfish — shad, skipjack herring, or another species. A few use dipbaits. I asked King and two other catfish tournament pros if they knew anyone on the competition scene who specializes in, or even uses, mussels. They didn't know of anyone.

It is interesting that blue cats eat mussels, shell and all, in the first place. More fascinating is that, at times, blues feed almost exclusively on them, yet we hear few reports lauding their effectiveness as bait. It presents a clammy sort of conundrum.

Seasonal Shifts

Blue cats are omnivorous, meaning that they eat a variety of prey types. They generally eat what opportunity presents, whether it's fish, mussels, insects, and crayfish, or a combination of those or more. Like many other fish, blue cats have a shift in diets as they grow. Smaller blues eat items like insects and small fish with larger blues switching to mostly fish, and at times, larger invertebrates, including mussels.

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Much of what we knew about basic blue cat diets came from a handful of studies done in the 1960s and 1970s. Several recent studies, however, provide a more in-depth look, including seasonal shifts and possible mechanisms driving catfish diets. Changing fisheries, which ultimately change available foods, are playing a role in blue-cat diets in many waters today.

Blues have always fed on native mussels, a diverse group with about 300 species in North America. Over the past couple of decades, however, exotic mussels have colonized many rivers and reservoirs where blue cats live. By the 1970s, the Asian clam, Corbicula, originating in southeast Asia and first introduced to the western U.S., was found throughout much of the Mississippi basin and Gulf Coast and eastern states. Zebra mussels, native to western Asia, were first discovered in the Great Lakes in the late 1980s and have since spread to many large rivers, lakes, and reservoirs in the eastern half of the U.S. These small and prolific exotic species threaten populations of native mussels and are providing a new food source for blue cats and other fish, such as freshwater drum and redear sunfish.

In lakes Marion and Moultrie on the Santee-Cooper system in South Carolina, a food habits study conducted in the late 1970s revealed that the most important foods for blue catfish were shad, Asian clams, and mayfly nymphs. Overall, clams were found in 37 percent of stomachs containing food, making up 34 percent of food weight. Fish were most important in winter and clams and mayflies were most important in spring and summer. Mayflies were eaten, mostly by smaller blues, while larger individuals ate mostly fish and clams. One 16-inch blue cat contained 157 clams.

A similar seasonal shift in diets was observed in Lake Norman, North Carolina. Joseph Grist, who studied the reservoir's blue catfish for his Masters degree at Virginia Tech, found that from 2000 to 2001, the most common items in winter diets were fish, primarily shad, and Chara, an aquatic macroalgae. From spring through fall, however, Asian clams were the dominant food, making up over 80 percent of food weight in summer. He also used transmitters to monitor blue cat movements, finding that blues with smaller home ranges were often over areas of clam beds. Grist reports that clams were more important to smaller blues, while fish were most important to the largest blues.

In the lower Mississippi River, Mississippi State University and U.S.G.S. Mississippi Cooperative Fish and Wildlife Research Unit biologists Michael Eggleton and Hal Schramm examined feeding of blue catfish in three habitats: main channel, secondary channel, and floodplain lakes. Blue cats ate a variety of prey types, and differences in diets among habitats generally reflected differences in prey types available. A seasonally high use of zebra mussels was seen in the main channel and to a lesser extent in secondary channel habitat. They observed that feeding on zebra mussels was particularly high around wing dikes and bank revetment.

Zebra mussels colonized Lake Dardanelle, Arkansas, in the early 1990s and have become an important prey for blue catfish there, reports Dan Magoulick of the University of Arkansas and Lindsey Lewis of the U.S. Fish and Wildlife Service. Zebra mussels were the primary prey eaten by 53 percent of the blue catfish, but there was a strong seasonal shift in feeding. Blue cats ate primarily mussels in summer, switching to shad in winter.

Shifts Explained

Despite the heavy consumption of mussels by blue catfish, which is mostly outside winter according to these studies (more on that finding later), little evidence suggests that they prefer to eat mussels. Rather, the sheer abundance of mussels presents a feeding opportunity. But some interesting connections among blues, baitfish, and mussels help explain seasonal diet shifts.

Besides being a biologist, Lindsey Lewis also is an avid blue-cat angler and an observer of catfish behavior. His interests find him scuba diving to watch catfish in Lake Dardanelle. Increased water clarity due to zebra mussel filtration has made underwater observation a bit easier, but it's still challenging in the lake's fertile water.

"Blues' instinctual behavior is to eat what forage is available at the least cost," Lewis explains. "There are so many zebra mussels that it's like a buffet line down there for the blue cats. Blues don't have to expend a lot of energy to eat them. The mussels are sessile, they don't move around, so blues don't have to chase them down. Energy is mainly expended on detaching them from the substrate and swallowing them."

Lewis says that the ease of feeding on the abundant zebra mussels isn't the only factor contributing to blues eating them. "In the summer, when blues are feeding on mussels, the costs of searching for and capturing shad are high. Shad are simply just too fast for blues to pursue and catch in warm water, so a shad diet just isn't practical. Plus, the low dissolved oxygen in summer makes cats sluggish, so why not just hang out and join the mussel buffet line on bottom, where it's easy to acquire a meal?

"It's not that blues won't feed on items besides mussels in summer. They basically eat anything they can. We've even found persimmons in their stomachs," Lewis says. "But where you find blues aggressively feeding in summer is in conjunction with schooling fish, like white bass and stripers. Blues associate with these schools and feed on the shad that white bass and stripers are injuring and killing. Fish like stripers actually benefit blue cats this way.

"A lot of folks think of all catfish as bottom or benthic species, but blue cats moving with these schools often traverse open water and even come to the surface after wounded, dead, or dying fish. When water quality declines or they are resting, they lie near the bottom or in structure and wait for an opportunity to drift by or conditions to become more favorable."

Blues are a schooling fish by nature, Lewis explains. "Some individuals have more solitary behavior, but mostly they stay focused as a group. When diving around schools, I've heard numerous species make clicking noises, which is a common way that many fishes communicate and function as a collective. Anyone who has caught a blue cat is familiar with the sounds they make, and it is likely that these sounds have a purpose. Whether I'm using nets or lines, I have regularly experienced long periods where there are no blues, and then a school will move through and the action is fast and furious and then, just as suddenly, the school has moved on.

"When blues get real big they tend not to move with the smaller fish. Big fish congregate but in loose packs, staying on bottom close to structure. These fish are really opportunistic, eating whatever they can get their mouths around. But if I'm after big fish, I'm going to use the forage they most ­prefer, and that's fish."

From an energetics perspective, shad and other fish like skipjack herring are more valuable to blues than mussels are. Shad have a significantly greater energy content, so a large mass of mussels needs to be eaten to equal what can be gained from a single shad, especially considering that mussel shells aren't digestible and make up a lot of the weight that's eaten. Still, even mussel meat has less caloric content than shad.

"Blues make a big shift from eating mussels to mostly shad in winter. In cold water, shad slow down and can't swim as fast, so it makes sense from an energetics perspective to make the switch," Lewis says. "When there's a winterkill, there are times when the bottoms of lakes are white with shad bellies. You see cold-stressed and wounded shad floundering near the surface, with the gulls, cormorants, and pelicans eating them. Unable to fight the currents, the shad drift and many get chopped or wounded in dam turbines and spillways, creating a conveyor of food for waiting predators. At times there's so many dead shad that they have even caused problems for water intakes.

"In winter, the energy costs of feeding on shad essentially drop to zero. It can get difficult to catch blues on shad in winter because the blues are just too stuffed. Commercial gill netters, however, often find it easier to catch blues in winter, because they're so plump they wedge in the mesh of the net more efficiently," he says.

Mussels Lure Cats

The life cycle of some freshwater mussels involves a cunning way of luring fish. Reproduction starts with male mussels releasing sperm into the water, which is siphoned in by a female where eggs are fertilized internally. The fertilized eggs develop into a larval stage called glochidia.

The next step involves getting the glochidia to attach to a host fish where the glochidia metamorphose, eventually breaking free to complete their life cycles as mature mussels. To attract host fish, which can be quite species-specific, the mussel makes its own lure. The lures of some mussels have lifelike detail and resemble baitfish or other natural prey. When a fish bites the lure, the glochidia are released into the water and attach to the fish.

The winged mapleleaf is a federally endangered mussel, with the only remaining populations in the St. Croix River bordering Minnesota and Wisconsin and in the Saline River in Arkansas. Biologist Mark Hove and his colleagues discovered that blue catfish and channel catfish are hosts to the larvae of the winged mapleleaf.

Hove: "A winged mapleleaf that's brooding young moves up out of the riverbed, and its mantle swells into a pouch. The larvae are held beneath the large triangular pouch that is colored with light and dark stripes. Biologists speculate that a blue or channel catfish bites down on the pouch and gets a mouthful of larvae. The catfish may swallow some larvae, but many of the glochidia attach to its gills."

Knowing a mussel species' host fish is important to rebuilding mussel populations. Biologists can "seed" host fish with glochidia in hatcheries and release those hosts into natural habitats.

Baiting with Clams

The bottom line is that blue cats should prefer baitfish over mussels. But if you want to experiment with ­mussels, you can look to two primary sources to gather bait. One option is to collect them in their natural habitat. Mark Hove, a mussel biologist at the University of Minnesota, says that anglers need to be careful about what mussels they harvest. A large percentage of native mussel species are federally protected or have special status within individual states, so it's best to know how to identify them and to follow the regulations concerning mussel harvest. Stiff fines can be imposed on someone in possession of a protected species.

Hove says that Asian clams are easy to identify with practice, because they're the only mussels with raised concentric rings on their shells. They're sufficiently abundant in some places that collecting enough for bait can be quick. He recommends using a sieve or colander. Sort through the gravel and look for clams that are typically an inch or less. Never move exotic mussels from one waterbody to another, which can speed the spread of nuisance species.

Shell the mussels, collect the meat, and skewer the meat on a hook. Use it on the same rigs as you would with other types of baits. Gathering ­summer-killed mussels is another option. Some say the slightly soured but not rotten clams are more attractive to cats.

Another good source of clam meat is commercial shellers. A few freshwater mussel species are commercially harvested, with much of the industry focused on processing shells for pearl seed stock. The shells are processed into small round bits called nuclei, which are seeded into oysters as a substrate for growing pearls.

You might try packing a handful of mussel meat into a small bag made of mesh material, like minnow-seine mesh or a piece of onion bag tied off to hold the contents. The bigger package is meatier and probably disperses more scent and flavor than would a few single mussels threaded on a hook. Plus, the mesh bag would hold to the hook well for longer casts, but mussels are tough anyway and really don't need extra hook-holding power.

Putting It to Bed

While King hasn't had success using mussels as bait, they're still part of his tactics in an indirect way. He knows the blues feed heavily on them, so he looks to mussel beds to find cats, but he fishes with cut baitfish. "I know some of the commercial mussel divers on the Tennessee River and I've learned the location of some beds from watching them," he says. "A lot of the beds I fish are on 20- to 25-foot flats.

"The best times to fish beds are early morning and later in the evening. The blues move up onto beds to feed during these periods. Most of the fish I catch are eating size. It's not uncommon for me and the clients to catch 80 to 100 pounds of 1- to 5-pound fish in a day." King primarily uses controlled drifting tactics, where the boat's drift speed is slowed by using a trolling motor against the river's current. Targeting blues on mussel beds is also a tactic used by some ­Santee-Cooper catmen.

Much of Hove's job as a researcher involves locating mussel beds. He says that beds tend to be diverse habitats relative to the surrounding waters. In addition to being food for blue cats, mussels also create substrates for colonization of aquatic invertebrates and plants, attracting smaller fish seeking food or cover. When scouting for mussel beds, Hove looks for gravel and rock along the banks of rivers, and beds are likely offshore around those areas. If a bank is sandy, chances are substantial beds don't exist along that shoreline. Mid-water shoals are also good spots to locate beds.

Like fishing for any species, there are situations when non-conventional presentations excel over the norm, which lends itself to keeping open the idea of experimenting with mussels. Give a blue cat a choice, however, and all evidence suggests that they'd prefer a juicy slab of high-energy baitfish. Seems both the science and the tournament pros have reached the same conclusion: Blues eat mussels, but they like fish.