Feeding Habits and Ecological Implications of the Invasive Flathead Catfish, Pylodictis olivaris, in the Susquehanna River Basin, Pennsylvania

Flathead Catfish _Pylodictis olivaris_ are a prominent aquatic invasive species within the United States and a recent invader in the Susquehanna River Basin, Pennsylvania. Flathead Catfish are piscivores known to consume native and recreationally important fish species. In the northeastern United States, it is unknown how this invader is impacting food webs and which species may be at greatest predation risk. To address this knowledge gap, we DNA barcoded stomach contents collected from Flathead Catfish to identify prey species and elucidate potential predatory impacts of Flathead Catfish in the Susquehanna River. A total of 576 Flathead Catfish were collected during 2020 – 2021, with 241 individuals having recoverable stomach contents. In all, we identified 47 different prey species. The most common prey species were rusty crayfish. While frequency of occurrence of prey species differed across Flathead Catfish length class. Rusty crayfish were commonly found (33.7 - 44.0% of diets) in stomachs of all size classes. We used a Bayesian hierarchical multivariate probit model to investigate if the probability of prey species occurrence in the diets of Flathead Catfish varied seasonally or as a function of Flathead Catfish length. We found that Flathead Catfish length and seasonality did influence prey occurrence probability differentially for a range of species. For example, Channel Catfish _Ictalurus punctatus_ were more likely to appear in shorter Flathead Catfish while Smallmouth Bass appeared in larger Flathead Catfish. We demonstrate significant variation in Flathead Catfish predatory effects that will be important to fisheries managers responsible for future management and monitoring strategies.

This repository provides R scripts to analyze diet data for Flathead Catfish sampled in the Susquehanna River, PA.