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FOOD WEB ALTERATIONS IN SUSQUEHANNA RIVER BY NON-NATIVE FLATHEAD CATFISH (PYLODICTUS OLIVARIS).

    Hodgson, Olivia, Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, och13@psu.edu; Stark, Sidney, The Pennsylvania State University, University Park, PA 16802; Kepler Schall, Megan, Department of Biological Sciences, Penns State Hazleton, 76 University Drive, Hazleton, PA 180202, mvk10@psu.edu; Smith, Geoffrey, Pennsylvania Fish and Boat Commission, Division of Fisheries Management, Bellefonte, PA 16823, geofsmith@pa.gov; Hopkins, Zach, Eastern Ecological Science Center, U.S. Geological Survey, Kearneysville, WV 25430, zrhopkins@usgs.gov; Tokranov, Andrea, Eastern Ecological Science Center, U.S. Geological Survey, Kearneysville, WV 25430, atokranov@usgs.gov; Smalling, Kelly, New Jersey Water Science Center, U.S. Geological Survey, Lawrenceville, NJ 08648, ksmall@usgs.gov; Wagner, Tyler, U.S. Geological Survey PA Cooperative Fish and Wildlife Research Unit, The Pennsylvania State University, University Park, PA 16802, txw19@psu.edu.

    Flathead catfish (Pylodictus olivaris), one of the world’s worst invasive species, were first detected in Pennsylvania’s Susquehanna River in 2002. Since then, they have established a growing population, expanding throughout the river system. While their predatory effects on native fish are known, their impact on river food webs is less understood. This study aimed to assess how flathead catfish invasion affects the trophic position and isotopic niche of the Susquehanna River food web by comparing invaded and non-invaded sites. Key species examined included crayfish, minnows, smallmouth bass (Micropterus dolomieu), and channel catfish (Ictalurus punctatus). Flathead catfish occupied the highest trophic position, with evidence showing a shift in the trophic position of resident species, especially channel catfish. Isotopic niche expansion and overlap were also observed, supporting the “trophic disruption hypothesis,” where native species change diets to avoid competition. Our results indicate that flathead catfish invasion is altering food web structure and energy flow in a large riverine ecosystem and contributes to the breadth of knowledge regarding how diverse ecosystems may respond to the introduction of a large, predatory fish species.

    flathead catfish, channel catfish, apex predator, food web