Invasive fish, Part 1 — The Situation

Invasive fish, Part 1 — The Situation
Joe Bruce with a mid-size snakehead. (Bill May photo)

“First, do no harm” is commonly, possibly erroneously, considered the first rule of medicine. Perhaps it should be considered the first rule of fisheries management.

Greater Chesapeake tributaries and beyond are now faced with a serious threats from three major invasive species: Blue catfish, flathead catfish and northern snakeheads. These are considered “invasive species” under the federal definition of “non-native species that cause harm to the economy, to the environment, or to human health” or under the broader definition of “reproducing and expanding beyond their initial areas of introduction.”


All three species have ardent advocates from sport fishing and economic viewpoints, yet federal and state managers are gravely concerned over the potential, long-term, deleterious effects on Chesapeake ecosystems with possible irreversible damage to fisheries and the economy of the region.

Blue catfish are the major concern. The state of Virginia introduced blue catfish into the James and Rappahannock Rivers in the early 1970’s and later into the York River. Today anglers all over the country and beyond are traveling to the James River to try for trophy catfish. A 102-pound blue catfish was taken in the James in 2009, and fish over 50 pounds are not uncommon. (A world record 143-pound blue catfish was caught in John H. Kerr-Buggs Island Lake, Virginia in 2011.)

Like flathead catfish, their native range is the Mississippi, Missouri and Ohio River drainages, where both species are highly regarded sport and food fish. But blue catfish have demonstrated a tolerance for brackish water, allowing them to migrate throughout the Potomac River as far north as Susquehanna flats, to all Atlantic slope rivers of Virginia and to at least the Patuxent, Elk and Nanticoke rivers in Maryland. The Potomac has become another target for trophy hunters producing blue catfish over 80 pounds. Many trophy fish are released throughout the blue catfish range.

A commercial fishery of over $1.7 million has developed.

Potomac guide Mike Starrett with a mid-size blue catfish. He and his clients have taken blue catfish more than twice this size.
Potomac guide Mike Starrett with a mid-size blue catfish. He and his clients have taken blue catfish more than twice this size. (Bill May photo)

Blue catfish are big, tasty, can be taken on basic, heavy bottom fishing tackle with bait and provide a good winter fishery. But they are fast breeding, long-lived (over 20 years) highly mobile, and devour such species as striped bass, shad, blue crabs, other catfishes, mussels, various panfish and baitfish and even insects and vegetation. And they can take over an area; blue catfish constitute 75 percent of the biomass in at least parts of the James River.

Flathead catfish are now found in the Potomac River, the upper Chesapeake Bay, and the Susquehanna, Elk and Sassafras Rivers. Virginia introduced the fish to Occoquan Reservoir; they then spread to the Occoquan River, which is part of the Potomac River. The species also spread from the Susquehanna River in Pennsylvania, where it was introduced, and into the upper Chesapeake Bay of Maryland with a sizable population below Conowingo Dam. (Another theory is that at least some these fish came from the New River in Virginia probably illegally transplanted.) There are growing populations in the upper Potomac River, but origin of this introduction is “unknown” according to the Maryland DNR.

Flatheads do not share the salt tolerance of blue catfish but can rival them in size, with specimens caught well over 100 pounds, and in predation. The species eats primarily fish and crustaceans and can quickly decimate native catfish populations and possibly sport fish, such as sunfish. Flatheads also appears to be a major threat to the smallmouth bass populations in the Susquehanna and Potomac both in preying on bass but also by drastically reducing their crayfish, panfish and minnow food base.

Northern Snakeheads have received media attention as “Frankenfish” because of their toothy and snakelike appearance and erroneous reputation for ability to walk on land. (Yes they can breathe air, allowing them to survive in low oxygen waters and out of the water for a time.) These fish were introduced by individuals. The northern snakehead is a native of the Yangtze River basin in China.

When snakeheads were found in Maryland in 2002, it was not illegal to possess live specimens nor to import them into the United States. When it was discovered that the species can proliferate in a temperate climate, it became a threat to Chesapeake area tributaries. Shortly thereafter the laws changed and it became illegal to possess live northern snakeheads in Virginia, Maryland, Delaware and other states.

It is illegal to import live snakeheads into the United States or D.C., or any U.S. territory or possession.

Snakeheads are not as large as the catfish species; the current Potomac record 18.4 pounds. However, they breed prolifically: Female snakeheads average about 40,000 eggs but can release up to 100,000 eggs and can spawn multiple times per year. They are also voracious predators of fishes, freshwater crustaceans, and amphibians.

But current studies by John Odenkirk of the Virginia Department of Game and Inland Fisheries indicates killifish and sunfish constitute over 90 percent of the diet of Potomac River tributary snakeheads.

With their tolerance of a wide range of at least freshwater conditions, it is feared they could become established throughout most of the contiguous United States and possibly adjoining Canadian provinces and, with their feeding style, could out-compete popular sport fish such as largemouth bass. However, guides and anglers report “everything eats snakeheads,” and Odenkirk feels that in the Potomac “competition does not appear to be occurring … but this could change.” Biologists are also concerned that they could introduce parasites and diseases that could harm native species.

Perhaps the major threat of snakeheads is illegal stocking, which is occurring in many Northern Virginia reservoirs, and illegal stockings of both catfish species is also occurring.


These invasives cannot be eliminated, so the management challenge, covered in Part 2, will be to somehow mitigate possible irreversible and severe environmental and economic damage while preserving current sport fishing and economic benefits.