Blue catfish stomachs reveal the environmental toll of their appetite Fisheries

Blue catfish stomachs reveal the environmental toll of their appetite  Fisheries







Anatomy of Noah Pressman

Noah Pressman, a biologist at the University of Salisbury in Maryland, begins dissecting a large blue catfish to determine its contents. stomach.



In terms of appetite and willingness to devour almost anything, experts say the blue catfish has few peers in the Chesapeake Bay.

“They eat everything, anything they can get in their mouth,” said Noah Pressman, a fish biologist at Salisbury University in Maryland.

Now, a clearer picture of its environmental toll is emerging. Two new studies conducted on tidal rivers on both sides of the Gulf show that invasive species are gobbling up valuable native aquatic life, such as menhaden and blue crabs, at high rates.

Previous studies have suggested as much. But the latest research adds important insights.

The investigation by Pressman’s team represents the first time the eating habits of non-Indigenous people on the eastern side of the bay have been examined. Meanwhile, Virginia scientists used a previous assessment of blue catfish stocks to produce another first: estimates of the amount of each species eaten within the main Chesapeake River.

The goal is to determine whether abundant and voracious blue catfish are endangering the survival of their prey within a particular river or even the entire bay complex. Many hunters and biologists have doubted this. They just lack scientific evidence to prove it.

The new research brings observers closer to that goal, said Dave Secor, a fisheries biologist at the University of Maryland Environmental Science Center. “Some of these numbers show very large potential impacts on predation on prey species,” said Secor, who was not involved in the studies.







Pressman on a boat

Noah Pressman, left, and Davis Carter catch blue catfish in Maryland’s Nanticoke River as part of the Marchhop Madness Blue Catfish Tournament.



Blue catfish arrived in the Bay Area in the 1970s, when Virginia introduced them as another option for anglers. They were originally thought to be restricted to fresh water. But the cultivated plants, which are native to the South and Midwest, have shown they can tolerate saltier water. They soon found their way into the many rivers surrounding the bay.

Blue catfish can grow to over 100 pounds, and feed on everything from underwater weeds to small striped bass. The issue prompted Maryland Governor Wes Moore to ask the federal government to declare a disaster for the state’s fisheries to open the door to financial aid for water and seafood companies. A National Oceanic and Atmospheric Administration spokesperson said the agency is “working as quickly as possible” to determine whether there is sufficient evidence to support the request.

Pressman’s study focused on the Nanticoke River, one of the largest tributaries of the Chesapeake River east of the Susquehanna River. The researchers also analyzed the Marchhope River, a stream that branches off the Nanticoke River.

Scientists worry that an influx of catfish could wipe out the fragile population of endangered Atlantic sturgeon that return to Marshhope each fall to spawn — the only waterway in Maryland where that happens.

Salisbury’s Zach Crum said the team was particularly curious to see whether landscape differences on the Eastern Shore — smaller watersheds, flatter terrain, and a greater prevalence of farmland — might affect what catfish eat. He was the lead author of the paper that was the subject of his master’s thesis.

The researchers split into two boats. The lead boat conducted “electric fishing,” sending an electrical current into the water to bring the fish to the surface. Those on the chase boat caught the startled fish with nets.

Scientists also collected samples caught by fishermen during fishing tournaments. Others were collected via trawl nets or trot lines, which are heavy fishing line fitted with baited hooks.

They examined 1,049 catfish, ranging in length from 3.5 inches to 43 inches. Just over half of them had food in their stomachs, including nearly 80 different species of fish.

The results showed that their diet varies throughout the year and according to their size. Compared to other Gulf rivers studied, blue catfish in the Nanticoke Complex fed more heavily on river herring, blue crab, white perch, and menhaden.

The research turned up only two striped bass, suggesting that blue catfish may not pose as big a threat to the species as feared, Crum said in the newspaper. No sturgeon found.

However, Secor isn’t ready to let blue catfish off the hook. Catfish are so ubiquitous that it doesn’t take much feeding on a particular species to make an impact, he said.







Blue catfish tournament

David Sikorski holds a champion blue catfish caught by 14-year-old Kenna Bear, left, of El Dorado, Md., during the Marchhop Madness Blue Catfish Tournament. The fish weighed 26.9 pounds.



Among the strangest items discovered was a partially digested wood duck. “We didn’t see any signs of hunting bullets, as if it was a duck that might have gotten lost after being shot,” Pressman said. “So, it appears that (catfish) are actively preying on this.”

The Nanticoke research was only able to determine the amount eaten by hundreds of catfish examined. What about the millions of catfish still in the water?

Armed with blue catfish population data for the tidal portion of the James River, which they had compiled in a previous study, a group of researchers led by Virginia Tech was able to estimate how many tons of prey were consumed by the invaders. The nearly 6 million sharks in the river as of 2015 devoured about 4,500 tons of aquatic life, according to their research published in October in the journal. Marine and coastal fisheries.

The biggest bite came from the shad family: more than 900 tons of gizzard, threadfin and other shad. The largest single prey class, meanwhile, was blue crab, with about 440 tons of crabs becoming food for catfish, the researchers said. This equates to about 5% of Virginia’s commercial crab catch that year.

Whether this jeopardizes the survival of the James blue crab population remains unknown. For that, scientists will need to survey James’s crab stock to compare losses, said Corbin Helling, who led the study as a doctoral student at Virginia Tech. The study of blue catfish is not related to his current work as a fisheries biologist for the USGS in Ohio.

“We are not able to model the responses of prey populations,” Helling said. “There’s still work to be done, I think.”

Striped bass account for about 6 tons of the James catfish diet. This remains a concern, Secor said. “That’s hundreds of thousands of striped bass,” he said. “So, even though striped bass rarely show up on (researchers’) charts, they abound.”

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