Coming to a river near you, the Flathead…

Mama always said, life is like a box of chocolates. You never know what you’re going to get.

Forrest Gump

While perusing Facebook one morning, I came across a picture that rather startled me in both a good and bad way. I’m a Facebook friend of long-time fishing guide, Lance Dunham, and in my feed was a report from a recent outing he made with clients. Typical of Lance were pictures of some very nice smallmouth bass, but there is always a smattering of other species mixed in. This is one reason I have always enjoyed fishing the Susquehanna and its tributaries: the diversity of species the river offers up. On any given day, one can tie into smallmouth bass, fallfish, northern pike, carp, channel catfish, walleye, rock bass, and musky. And Lance’s post proved you can now add another species: the flathead catfish. But whether this is a good or bad species to add to the list is up for speculation over the longer term.

The flathead catfish has been grabbing news headlines over the years in towns and cities around the lower Susquehanna River. In 2020, a 56 lb. fish was caught, establishing a Pennsylvania state record. 3 years later, the state record was broken again by a 66 lb. flathead caught in the Susquehanna near Conestoga, PA, roughly 30 miles southeast of Harrisburg.

The record-setting angler was fishing with a friend in a very deep channel of the river known as Lake Aldred. He had baited a live rainbow trout onto a large circle hook with a 1.5-ounce sinker. The pair had four lines in the water at once and it wasn’t long before they had 3 hook-ups – landing a 30 pounder, a 45 pounder, and finally the new state record fish.

The huge flathead catfish officially weighed 66 pounds and 6 ounces, exceeding the previous state record by more than 10 pounds and measured 50.25 inches long with a girth of 35 inches. To show just how large flatheads can grow, Pennsylvania’s record is just half the world record, set by a 123 lb. fish caught out of a reservoir in Kansas!

The fish was released alive by the Pennsylvania game warden certifying the record. I found it odd that the angler was using a gamefish for bait, but Pennsylvania allows the use of gamefish for bait as long as they are fished whole. More interesting was the fact that such a fish with a record of being “invasive” was released alive.

Turns out the topic of “invasive” is in itself confusing. The flathead catfish (Pylodictis olivaris) is native to the Mississippi River basin, which includes parts of western Pennsylvania—specifically the Ohio River drainage. So, while it’s native to the greater state of Pennsylvania, it’s only truly native to that western sliver of the state, and certainly not native to the Susquehanna River basin, where it was first detected in 1991. It has since spread rapidly.

Flathead catfish are apex predators, sitting at the top of the food chain. Once introduced to the Susquehanna River, they’ve begun reshaping the ecosystem in dramatic ways that include predation of native species such as smallmouth bass, channel catfish, baitfish, and even crayfish. Their presence also forces other species to change their diets and habitats to avoid competition or predation. Channel catfish, for example, feed lower on the food chain in areas where flatheads are present. And because of this broad dietary overlap, ecological balance can be affected. Smallmouth bass, channel catfish, and carp all feed on crayfish, making the flathead just one more “consumer” of that resource.

Pennsylvania is taking steps to manage this invasive species. There is no creel limit for flatheads, for example, and catfish is a good eating fish. While there is a creel limit for channel cats in Pennsylvania – 50 per day – New York has no creel limit. One has to wonder if at some point these limits will be adjusted due to the flathead’s predilection for eating anything that swims.

In addition to the absence of a creel limit, there is also no mandate that flatheads be killed, such as is the case for snakeheads in Pennsylvania, which must be both killed and reported. In waters like the Delaware and Susquehanna River basins, anglers are only encouraged not to release Flatheads, regardless of size.

The concern of the flathead’s opportunistic predation and its potential to decimate native and recreational fisheries has led a team of researchers from Penn State, the U.S. Geological Survey (USGS), and the Pennsylvania Fish and Boat Commission to assess how flatheads are affecting the food web and energy flow in the Susquehanna River in Pennsylvania.

Their research found that flatheads had the highest trophic position – the level an organism occupies in a food web, based on its feeding relationships – even higher than resident top predators such as smallmouth bass and channel catfish. Channel catfish had a lower trophic position in areas populated with flathead catfish. This means they had to eat lower in the food chain, likely because they are being outcompeted by flatheads or avoiding them. In areas with flathead catfish, they also found all species showed broader and overlapping diets.

The research suggests that resident species are changing what they eat to avoid competing with or being eaten by the invader. The research also supports the ‘trophic disruption hypothesis,’ that says when a new predator enters an ecosystem, it forces existing species to alter their behavior, diets and roles in the food web. This can destabilize ecosystems over time. The 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.

In addition to evaluating trophic position, the researchers also analyzed the isotopic niche occupied by the fish species – the range of carbon and nitrogen markers found within the tissues of an organism, reflecting its diet and habitat, providing insights into its ecological role.

To reach their conclusions, the researchers employed stable isotope analysis, a widely used tool that can explain patterns within a food web, highlighting links between trophic positions, as well as the breadth and overlap of trophic niches.

When fish eat, their bodies incorporate the isotopic signature of their food. By sampling their tissues, scientists can measure nitrogen isotopes and determine their diet, carbon isotopes to determine habitat use, and compare isotopic signatures across regions to deduce fish migration or habitat shifts. For this study, channel catfish, smallmouth bass, minnows and crayfish were selected as focal species because a previous diet analysis conducted in collaboration with Penn State, USGS, and Pennsylvania Fish and Boat Commission researchers within the Susquehanna River, showed that these species are important prey for flathead catfish.

“Flatheads grow fast in this river system, attain large body sizes and can eat a variety of prey,” said study author Olivia Hodgson, a master’s degree student at Penn State University. “Because adult flatheads have few natural predators, flathead catfish can exert strong control over the ecosystem.”

But invasives are nothing new. Zebra mussels, carp, Didymo, hydrilla, rusty crayfish, gobies – our waters have weathered all manner of invasives with different results. The St. Lawrence is one system hugely impacted by zebra mussels. I can recall fishing there in the 90’s when pike were plentiful in vast aquatic weed beds. Zebra mussels changed all of that – the water is now crystal clear, favoring smallmouth bass and diminishing northern pike populations.

I had the opportunity to discuss the invasion of the flathead during an outing with guide local guide Jimmy Kirtland of Row Jimmy’s guide service. Kirtland guides on the Susquehanna and other local rivers for smallmouth bass, channel catfish, and musky. His response to whether flatheads will truly change the fishing was muted, saying there is often a lot of anxiety to the news of invasives, but things tend to work themselves out in the long run and not become the environmental disasters that were originally feared.

The primary method of catching flathead on rod and reel is using live or cut bait. Flatheads are very different from channel catfish. They have relatively small eyes whereas channel catfish have large eyes.

And flatheads, especially the large ones, prefer live bait, and less so dead or even the stinky kinds of baits used for channel catfish. They prefer to feed at night but can be caught during the day around submerged structure, especially wood snags. The larger fish tend to be loners and will be very aggressive towards any fish, including their own.

But can they be caught on a lure or better yet, the fly? The fact that Lance Dunham’s clients are catching them is evidence of their taking a lure. But the fly? The answer is yes and I didn’t have to look far on the internet to find that answer. Flylords Mag featured an account of an outing by two anglers in eastern North Carolina. While sight fishing for longnose gar on a local river in low, clearwater conditions, these anglers stumbled upon a group of flatheads…

My buddy was in front of me and reached the pool we had in mind first, and yelled that there were 4 or 5 GIANT CATFISH. I didn’t realize how big he meant until I caught up with him and looked where he was pointing. These absolute giants were congregated and slowly cruising around at the top of the hole, and we both started freaking out. I had broken my 9wt earlier in the week and was using my 8wt with a slightly sinking tip. I tied on an EP brush fiber & deer hair gamechanger fly I tied the night before. I cast to the closest fish and just hovered it in front of its face, with a few short and abrupt strips. I immediately froze for a moment as I saw its mouth open and engulf the fly. The fish kind of turned in confusion for a slight second and shot downstream as it realized it was hooked.

I held on to my rod and barreled downstream after it, tearing my legs up in the process. I knew this was the biggest catfish I’d ever hooked and my mind was just racing. The pools are closely connected and are very deep so I had to plan on where to step accordingly. This didn’t really work out as I fell many times just to keep up with this fish, but I didn’t care. It seriously felt like I had hooked into a truck, and I was the one being controlled. I get crap constantly from my buddy’s because I use straight 35-pound mono as my short leader (for toothy gar and bowfin) but I was glad I didn’t have anything less than it on. I truly did not think I was going to land this fish because for every inch I got on him, he took back two feet or more. At the bottom of the third or fourth massive pool, the catfish realized it couldn’t go any further downstream as the river started to shallow up, and decided it was heading back upstream. I obliged. After a fight close to 45 minutes, and when fish was finally growing tired I managed to guide it into one of the open rock crevice areas where I felt I could most safely unhook it and admire it.

To pursue these fish on the fly, think very large flies with lots of movement, fished deep in snaggy structure by day and in shallower areas adjacent to holding water at night. Gear would need to be of the salty type – a 9 – 11 weight fly rod, big reels spooled with lots of backing and depending on the depth fished, intermediate to sinking fly line and a heavy, 30 pound-plus, short leader.

It’s likely that guide Lance Dunham’s future fishing reports will include more flatheads being caught, but will the smallmouth bass make less of an appearance going forward? As a long-term fly angler of the Susquehanna and its smaller tributary rivers, I’m never disappointed when I run into channel catfish. While I’d hate to see the balance that exists now shift largely in favor of “the invader”, the thought of hooking up with one of these river monsters on the fly sings a siren’s song…