Trophic Relations of Introduced Flathead Catfish in an Atlantic River

Abstract

The flathead catfish Pylodictis olivaris is a large piscivore that is native to the Mississippi and Rio Grande river drainages but that has been widely introduced across the United States. River ecologists and fisheries managers are concerned about introduced flathead catfish populations because of the negative impacts on native fish communities or imperiled species associated with direct predation and indirect competition from this apex predator. We studied the trophic relations of introduced flathead catfish in an Atlantic river to further understand the effects on native fish communities. Crayfish (Astacidea) occurred most frequently in the flathead catfish diet, while sunfish Lepomis spp. comprised the greatest percentage by weight. Neither of two sympatric imperiled fish species (the federally endangered Cape Fear shiner Notropis mekistocholas and the Carolina redhorse Moxostoma sp., a federal species of concern) was found in any diet sample. An ontogenetic shift in diet was evident when flathead catfish reached about 300 mm, and length significantly explained the variation in the percent composition by weight of sunfish and darters Etheostoma and Percina spp. Flathead catfish showed positive prey selectivity for taxa that occupied similar benthic microhabitat, highlighting the importance of opportunistic feeding and prey encounter rates. Flathead catfish displayed a highly variable diel feeding chronology during July, when they had a mean stomach fullness of 0.32%, but then showed a single midday feeding peak during August (mean fullness = 0.52%). The gastric evacuation rate increased between July (0.40/h) and August (0.59/h), as did daily ration, which more than doubled between the 2 months (3.06% versus 7.37%). Our findings increase the understanding of introduced flathead catfish trophic relations and the degree of vulnerability among prey taxa, which resource managers may consider in fisheries management and conservation of native fish populations and imperiled species.

ACKNOWLEDGMENTS

We thank Jim Rice and Cavell Brownie for their suggestions and logistic help during this research. Michael Fisk, Ed Malindzak, Patrick Cooney, Rupert Medford, Ryan Spidel, and Jenny Winters assisted with field collections. Keith Ashley, Bob Curry, Ryan Heise, Kent Nelson, Bill Pine, Tom Rachels, Wayne Starnes, Scott Van Horn, and Christian Waters facilitated sampling design and grant administration. Wayne Starnes confirmed identification of some prey items, and Chris Butler offered suggestions on cumulative prey curves. Any use of a trade, product, or firm name is for descriptive purposes only and does not imply endorsement by the U.S. Government. This research was funded by a grant from the North Carolina Wildlife Resources Commission through Federal Aid in Sport Fish Restoration Funds (Project F-68).

²The unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, U.S. Geological Survey, U.S. Fish and Wildlife Service, and Wildlife Management Institute.