Flathead catfish poses risk to native N.C. fish species Anglers love the flathead catfish because it's big, it puts up a good fight and it tastes good. But the flathead has a dark side: It needs to eat living fish, and lots of them. This attribute has fisheries and wildlife officials worried about some native North Carolina fish species, including the redbreast sunfish, white catfish and bullhead species, and small madtoms, which have all seen a population decline in areas where the flathead has been introduced. This trend is also causing concern in other states along the Eastern Seaboard, all the way from Florida to Pennsylvania. Dr. Tom Kwak, associate professor of zoology at North Carolina State University and unit leader of the N.C. Cooperative Fish and Wildlife Research Unit, is the principal investigator of one of the first extensive studies of the flathead catfish. The N.C. Cooperative Fish and Wildlife Research Unit is a partnership of the U.S. Geological Survey, the N.C. Wildlife Resources Commission, NC State University and the Wildlife Management Institute. Flathead catfish are not native to North Carolina, Kwak says; the species was introduced in the state in the mid-1960s as a sport fish. Little did N.C. officials know back then that the flathead, which seems to get along well with other fish in its natural habitat - the Mississippi River and its tributaries from Minnesota to the Gulf of Mexico - would put its carnivorous traits to use in harmful ways. "The flathead catfish is unique among American catfish in that it is an obligate carnivore - it must eat living fishes or other living invertebrates like crabs or crayfish," Kwak said. "It won't eat plants or other dead material, and you can't catch it with popular catfish baits like cheese or chicken liver." And it needs a lot of live fish to grow, Kwak says. To gain one pound, flatheads must eat about 10 pounds of live food. That adds up to a feeding frenzy when you consider that the largest flathead captured in North Carolina tipped the scales at 69 pounds, and the world record is a 127-pounder caught in Kansas. Kwak's cooperative unit was called in when biologists from the N.C. Wildlife Resources Commission noted that the numbers of native N.C. species began showing declines in areas inhabited by flathead catfish. His team joined Wildlife Commission biologists to determine if there is merit to the theory that the presence of flatheads leads to reduced numbers of native species like redbreast sunfish and other types of catfish, and also to discover how these fish behave and what types of habitats they use in North Carolina rivers. To learn more about the flathead catfish, the team - which includes NC State zoology faculty Dr. James Rice, Dr. Richard Noble, Dr. Joseph Hightower, doctoral student Bill Pine, research associate Scott Waters and a number of NC State graduate and undergraduate students - studies flathead populations in three eastern North Carolina rivers: the Northeast Cape Fear River near Burgaw, Contentnea Creek near Kinston and the Lumber River outside Lumberton. The team's focus is on three objectives: to ascertain approximate numbers of flathead catfish, along with other population characteristics like size and growth rates; to gauge the behavior and migration patterns of flatheads; and to determine the predator-prey relationship between flatheads and other fish. To accomplish these goals, the researchers collect flathead catfish by electrofishing - that is, generating low frequency electrical current in the water and then catching the stunned flatheads as they float to the surface. Researchers then measure and weigh each fish; mark all fish with small computer chips called passive integrated transponder tags that each have a unique number; and pump the stomachs of the fish to determine the fish's diet. A select number of flatheads - at least 12 in each of the three areas studied - also have a radio transmitter implanted so researchers can track movement and behavior. Some of the research findings have been surprising, Kwak and Pine say. It appears that the flathead catfish is thriving, but acting differently, in its non-native North Carolina environment. Flathead densities in the Neuse River system are greater than those reported in its native Mississippi River basin, the researchers say. Moreover, many flatheads migrate further than previously expected. "Based on one study in tributaries of the Mississippi River, it was assumed that in the flatheads stayed within one mile of where they were found," Kwak says. "In North Carolina, many are moving a lot, sometimes up to 30 and 40 miles of where they were originally found. This has serious management implications because flatheads are not just isolated in small areas, but moving throughout an entire river basin." The study also shows that flatheads are frequently found in deep holes in the river, especially habitats with cover, such as log piles or other woody debris. Stomach content analysis shows that flatheads consume a wide variety of prey items, including sunfish, crayfish, and occasionally shrimp and small crabs, Pine says. The flathead was recently spotted in the upper Cape Fear River, raising fears that a rare, endangered fish native to that river, the cape fear shiner, could be in trouble. Kwak and other NC State researchers and students are currently conducting habitat studies on the cape fear shiner, and may eventually examine the relationship between this small minnow and the flathead. Kwak has two suggestions to control the flathead population in the state. "Anglers should definitely practice catch-and-keep when they get a flathead catfish," he said. "And while it's illegal to move fish around from one river to another, someone moved the flathead into the upper Cape Fear. You're not doing anyone any favors by introducing the flathead into new waters; it's destructive to our native fisheries, and it's irresponsible." The information gained in this research will help state biologists work together with the public to manage fisheries to protect the state's native natural heritage. The final report on the impacts of flathead catfish in North Carolina will be released next summer.