Flathead catfish have become a threat to resident species in the Susquehanna River in Pennsylvania. The results of a new study suggest they're outcompeting other predators and reshaping an essential ecosystem.

What's happening?

Researchers from Pennsylvania State University, the Pennsylvania Fish and Boat Commission, and the United States Geological Survey say the invasive flathead catfish is impacting the Susquehanna food web and the feeding habits of resident species, according to a new study published this September in the journal Ecology.

Native to the Mississippi River basin, this catfish species was first identified in the Pennsylvania river in 1991, a news release from Penn State explained. The flathead has now assumed apex predator status there, where its more recent position at the top of the food chain appears to be sidelining resident predators, such as smallmouth bass and channel catfish.

"Flatheads grow fast in this river system, attain large body sizes and can eat a variety of prey," study co-author Olivia Hodgson said in a statement. "Because adult flatheads have few natural predators, flathead catfish can exert strong control over the ecosystem."

Left unchecked, the impacts of invasive species on food webs can undo ecosystem balance. The co-authors wrote that their results "support the 'trophic disruption hypothesis,' where an introduced species prompts resident species to change diets in an attempt to avoid competition and predation following invasion."

The researchers found that in portions of the Susquehanna River that flathead catfish now occupy, channel catfish appear to be eating lower on the food chain to avoid this competition, according to the release. In fact, in those areas, "all species showed broader and overlapping diets."

Why is this concerning?

Healthy populations of resident species are crucial to resilient, sustainable ecosystems. Already well-adapted to their habitats, native plants and wildlife help to maintain a kind of harmony there and keep food supplies stable.

The introduction of invasive species — often a result of human activity — can threaten local biodiversity, as new predators outcompete others for food sources, potentially starving various lifeforms and limiting their reproduction.

But Hodgson notes, "Our study highlights how an invasive species can do more than just reduce native populations — it can reshape entire food webs and change how energy moves through ecosystems."

What's being done about this?

There are several key ways to curb the spread of invasive species, whether of the flora or fauna variety.

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In terms of aquatic life, expert-organized fishing festivals aimed at managing invasive populations have shown success. Officials have encouraged locals to put safe and edible invasive species on the menu ahead of struggling native species in some cases.

Avoiding the introduction or spread of invasive species to new environments is also key, and that's true in rivers and in gardens. And cultivating native plants at home can guard against biodiversity loss in more ways than one. Rewilded yards and natural lawns make welcoming habitats for the pollinators that nurture numerous species in a sustainable balance.

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