Bay Journal

Blue catfish taking bite out of key species

Predator’s impact on blue crabs, menhaden and blueback herring populations greater than expected.

  • By Karl Blankenship on November 24, 2013
  • Comments are closed for this article.
Mike Drayton caught these blue catfish in the Potomac River near Fort Washington, MD.  (Dave Harp)

A new study confirms that nonnative blue catfish around the Chesapeake have the potential to take a significant bite out of populations of important native species such as blue crabs and river herring.

The study examined the diets of blue catfish in portions of several Virginia tributaries and concluded they “may contribute to substantial losses of key fishery resources.”

Those losses could be “ecologically significant” for some species such as blueback herring, whose populations are already at low levels, the study concluded.

It also said blue catfish predation could have a greater impact on abundant species, such as blue crabs and menhaden, than previously thought. In part, that is because blue catfish are turning up in higher salinity water than expected.

“To me, the most surprising finding from our study was the extent to which we documented predators much farther downstream in the James — down to the Chesapeake Bay estuary proper,” said Greg Garman, director of the Virginia Commonwealth University Center for Environmental Studies and lead author of the study. “We wouldn’t have expected that.”

The study comes as the Bay Program’s Sustainable Fisheries Goal Implementation Team in December is expected to review possible management options to reduce threats posed by blue catfish.

It was one of several research projects supported by the National Oceanic and Atmospheric Administration Chesapeake Bay Office to better quantify the level of threat blue catfish may, or may not, pose to other Bay species and resources.

Concerns about blue catfish have been growing as their numbers have exploded around the Bay. The large predatory fish were introduced into the upper tidal James River by the Department of Game and Inland Fisheries in the mid 1970s, a time when introducing new species for recreational anglers was common practice.

Over time, their numbers have dramatically increased. They populate the tidal portions of all major Virginia tributaries, the Potomac. In recent years they have been turning up in many Maryland tributaries, as well.

Blue catfish, which in rare cases can reach 100 pounds, can dominate rivers where they are introduced. In the James River near Hopewell, for instance, scientists estimate they account for 50–70 percent of all fish biomass. Scientists and fishery managers are worried that could mean trouble for native species if they are eaten in large numbers by blue catfish.

The new study examined 1,002 blue catfish 15 inches or longer that were taken from the Rappahannock and James rivers during the fall of 2011 and spring of 2012. They found that blue catfish ate a wide variety of species, including many of management concern such as blue crabs, blueback herring, American shad, softshell clams, menhaden and white perch.

Based on those results, the researchers estimated what the potential predation by blue catfish might have been during spring 2012 in two specific locations.

In Burwell Bay, a small area of the James River not far upstream from Newport News, they estimated blue catfish had the potential to consume 560,000–720,000 blue crabs. For perspective, that would be nearly 1 percent of the 765 million blue crabs estimated to be in the Bay in early 2012 by the annual Blue Crab Winter Dredge Survey.

In that same area, the study estimated blue catfish may have consumed 670,000–820,000 Atlantic menhaden and 1.9 million–3.1 million softshell clams.

Farther upstream, near Manchester, they estimated that blue catfish might have consumed 8,000–10,000 blueback herring — a once-abundant species whose East Coast population is at a record low — and 14,000–18,000 white perch.

“If those estimates are even close to being correct — and I’m pretty comfortable with them — you can imagine that that level of predation is probably going on at other places within the Bay, and maybe over even longer periods of time,” Garman said.

Scientists conducting the study found blue catfish in salinities up to 17 parts per thousand. Before this, fishery scientists thought their salinity tolerance was 14 parts per thousand. The researchers expressed concern that the species may eventually occupy an even larger range around the Bay than previously thought.

Bob Greenlee, a fisheries biologist with the DGIF, said he wasn’t surprised by the findings. Previous studies by the department had suggested that blue catfish can zero in on whatever prey is abundant at a given time and given place.

Because blue catfish are such opportunistic feeders, he said, it is hard to infer from one study what overall impact they have on a given resource. “Wherever you get a sample in these rivers, and its timing in a given year, is going to influence what you say the blue catfish diet is,” he said. “If it’s an abundant resource, they are targeting it.”

Greenlee expressed doubt that much can be done to control blue catfish in the region because their population is well-established, and well-adapted. “Given the status of the species in the watershed and lack of viable management options,” he said, “it is highly unlikely we are going to control the species in the Bay.”

About Karl Blankenship

Karl Blankenship is editor of the Bay Journal and executive director of Chesapeake Media Service. He has served as editor of the Bay Journal since its inception in 1991. .(JavaScript must be enabled to view this email address).

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Just finishing the facts on November 25, 2013:

I think this article is one sided against blue catfish. The study only checked the stomach contents of one predator, while neglecting other species in the ecosystem. To just say that the Blue Catfish is harmful because it ate so much of one species or another while neglecting the impact of other predators. Look at the resurgence of the striped bass, whose diet is primarily those same fish that they they follow up into the bay, eating breeding stock fish before, during and after they breed. The crab population, and winter dredge were higher this year than they have been in years. White perch are so populous that MD DNR has no size limit on the fish, or creel limit on them. Blueback Herring come into the bay around the same time that Striped Bass start migrating up to spawn as well. What kind of lures to most anglers troll behind their boats for Striped Bass during spring season? Oh those that look like Menhaden, Blueback Herring, American Shad, and Hickory Shad. Why? Because Striped Bass don't like them and want to kill them but don't have hands. Oh wait, Striped Bass actually eat everything (and more) on that same list worried about , and travel with the schools of migratory fish to feed on them...

Mark Orlicky on December 03, 2013:

The study that this article talks about is a snapshot in time. It talks about what is going on now, what the blue cats are eating. But, what was the situation like before the blue cats were introduced into the James? And, what were the populations of the bluebacks, stripers, menhaden, and shads back then and now? I know that the Department of Game and Inland Fisheries had reasons for the introduction of blue cats into this area... it wasn't just to provide recreational anglers with another option. I'm sure a fisheries biologist saw a void, a niche that the blue cats could fill. And, they've done well. Catfish adapt well. Are the blue cats displacing another predator, such as the smallmouth bass? Or, the striped bass? The study didn't pursue that line of thought. I say, lets praise this success story. The blue cats in the James have done well. They're growing to immense sizes and they are a good fighter. Sportsmen come to the area to fish for them. Note the number of guides that specialize in blue cats. For those that like to eat their catch, the blue cat is a very tasty fish. Quite delicious. I say, lets be happy with this success story. They're a valuable resource!

Alonso on December 03, 2013:

The article isn't saying that the blue catfish is solely or even the main factor in the declines, it is saying it is a large predator adding additional predatory pressures that shouldn't be there since it is not a native fish. Not only is the catfish eating the species mentioned, but as the last post mentioned, it is also competing with native fish like striped bass and likely affecting their health and numbers as well. All in all, when we introduce non native species, it affects those native species that are present and almost always in a negative manner. The blue catfish doesn't belong there and is affecting the native species negatively through predation and competition.

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