September 16, 2015
The Bad & The Good, Then & Now
Catfish, for better and for worse, have been spread widely throughout North America. The native range of the "big three" catfishes — blues, channels, and flatheads — stretches from the Appalachian Mountains to the Rockies and from the Hudson Bay drainage to the Gulf of Mexico. Of the big three, the channel catfish is the most widely distributed outside its range, and introductions have attracted little if any negative attention. But hell broke loose when the flathead catfish showed up in Georgia and North Carolina rivers. And blue catfish are climbing the most-unwanted list in Georgia and Chesapeake Bay. The reason: blues and, especially, flatheads are voracious piscivores, and their giant size means they can eat a lot of fish, including large fish.
And eat fish they did, particularly flatheads. I reported on the wave of terror from flathead catfish introductions in the 2008 Catfish Insider Guide. Here's a brief recap of the problem.
The first known introduction of flathead catfish east of the Appalachians was attributed to an angler introduction into the Flint River, Georgia, in the 1950s. (Incidentally, this population was studied in the 1980s by a bright, young Georgia DNR biologist and now In-Fisherman Senior Editor Steve Quinn.) Regrettably, in hindsight, some introductions were made by several state fisheries agencies in the Southeast. South Carolina stocked flatheads into the Santee-Cooper reservoirs in 1964, and North Carolina stocked the Cape Fear River in 1966.
But anglers — like Johnny Appleseed with a livewell — spread flatheads into other Gulf and Atlantic coast rivers. Flatheads are now established in almost every coastal river in Georgia, North Carolina, and South Carolina. They are in the Apalachicola and Ochlockonee rivers in Florida. They are in Virginia's James and Potomac rivers where they share problem status with introduced blue catfish. And they're in the Schuylkill and Susquehanna rivers in Pennsylvania.
In the wake of the expanding flathead populations, highly valued redbreast sunfish and native catfish populations crashed. In Georgia's Altamaha River, for example, redbreast sunfish declined 80 percent. In the Cape Fear River, redbreast sunfish have been severely reduced, native bullheads and white catfish have been eliminated, and ongoing extensive and expensive efforts to restore native anadromous American shad are threatened.
Some anglers recognized the sport and table-fare qualities of the introduced flatheads and directed their fishing effort toward them, but die-hard redbreast sunfish anglers were incensed. Georgia DNR surveyed Altamaha River system anglers in 1997, 20 years after the first flatheads showed up. Even though many anglers had begun to exploit the burgeoning flathead population, half of the anglers supported reducing the flathead catfish population. Two-thirds of surveyed anglers supported sport fishing or a combination of sport and commercial fishing to reduce the population.
I ended that report with questions that are important to fisheries management and to anglers:
What is the carrying capacity — the biomass of a species that the habitat can support on a sustained basis — for flathead catfish, and what will be their long-term impact when they reach carrying capacity? Introduced fishes that establish populations typically go through an expansion phase. With numbers low and well below carrying capacity, growth rate is fast, recruitment is strong, and the density and biomass of the population increases. Often, an introduced population overshoots its carrying capacity. When resources — almost always food — become limiting, growth slows, recruitment slows, and population numbers and biomass decline to carrying capacity. This may be a good thing because the impact on other fishes declines. While a flathead population stabilized at carrying capacity has less impact, achieving that stability may be scary if these predators decimate everything in sight before declining to carrying capacity.
The Georgia Department of Natural Resources was about to launch an aggressive flathead removal program. Would these "maintenance control" efforts be successful? As is true for any aquatic invasive species, eradication of flathead catfish is not possible. Other efforts to control deleterious invaders, such as common carp in the Midwest and brook trout in western streams, have failed. However, population modeling suggested that achievable exploitation rates could reduce flathead populations to low levels.
While fishery managers frequently impose harvest restrictions to prevent overfishing, angler overharvest of flathead catfish in Georgia rivers is unlikely given low angler effort directed at flatheads and fish consumption advisories that discourage harvest. Thus, DNR-conducted electrofishing search-and-destroy efforts seemed to be the only option to see whether flatheads could be controlled and native fisheries would rebound.
How will the native fish assemblage respond after flathead catfish are integrated into their new home? Flatheads aren't a problem in their native range where they're just another predator, accused of no sinister activities, and actively pursued by a cadre of anglers who long to subdue one of North America's largest and hardest fighting gamefish. And that leads to a most significant question.
How will anglers respond? Some anglers are distraught that these unwanted invaders have destroyed their highly valued native fisheries. Yes, this is a culture thing, but it's also about fishing idyllic settings and catching world-class redbreast sunfish, what the "low country" folks call "rooster reds." Will anglers adopt the flathead as a preferred sportfish? Culture runs deep, especially in the South.
Invasive Catfish 2015: What Fishery Managers Have Learned
Valuable published information about blues and flatheads is available from many sources, but particularly the American Fisheries Society book Conservation, Ecology, and Management of Catfish (fisheries.org/shop/54077c). Intel from fishery biologists Tim Bonvechio and Don Harrison in Georgia, Dr. Tom Kwak in North Carolina, and Aaron Bunch and Bob Greenlee in Virginia, helped provide In Fisherman readers the most up-to-date information available.
Population Dynamics of Fathead Catfish — Flathead catfish showed up in Georgia in the Flint River in the 1950s and in the Altamaha River in the 1980s. The populations were estimated at 175 pounds per acre in the Flint in 1985 and 294 pounds per acre in the Altamaha in 1995. In 2007 to 2009, the biomass had dropped to 21 pounds per acre in the Flint and 46 pounds per acre in the Altamaha. "Stabilized" in the fish world doesn't mean constant or without fluctuation, but it appears that flathead populations in both the Altamaha and Flint rivers have leveled out at a standing stock far below the populations levels during the early expansion phase. Growth rate has slowed in both populations.
Flathead catfish are less intensively monitored in North Carolina's coastal rivers, but routine sampling indicates the populations are abundant and fairly stable. In Virginia, the James and Pamunkey rivers support only modest numbers of flatheads, and most fish in the James River are 24 to 34 inches, suggesting limited recruitment. However, flatheads have expanded into interior rivers.
Population Dynamics of Blue Catfish — Blue catfish are relatively new invaders in Georgia. They were first detected in Lake Sinclair in 1996 and in Lake Oconee in 1997. In Lake Oconee, the population remained low until 2002 and then began a rapid rise. Individual fish grow fast, and the population appears to be expanding. Formerly abundant white catfish began to decline in 1998 and are now rare. It's not clear whether the apparent demise of white cats is a result of competition or predation by blues. Channel catfish abundance since the introduction of blues may now be trending downward as well.
Blue catfish were first detected in the Altamaha River in 2006. The young population is reproducing and rapidly increasing, and individual fish growth rates exceed those of blues elsewhere. Although Georgia DNR biologists report no declines of native catfishes, the Altamaha has already been impacted by flathead catfish. A limited food habits study indicates the diet of blue catfish is dominated by Asiatic clams, and fish over 24 inches are also eating introduced freshwater prawns. Fish are a minor component of their diet; unfortunately, most of the fish eaten were American eels, a species of special concern throughout the eastern U.S. These findings are quite interesting because clams and prawns are low-energy foods compared to fish and are not a diet conducive to fast growth.
Blue catfish numbers in North Carolina coastal rivers have fluctuated widely over time. Populations appear vulnerable to hurricane-generated floods and the low oxygen conditions that typically besiege coastal rivers when the torrential rains wash huge quantities of organic matter downstream and flush backwaters.
Blue cats were stocked into Virginia's tidal rivers in the 70s, but standardized monitoring did not begin until 2000. Although varying among rivers, the populations have peaked and seem to be trending downward. The trophy fishery in the James may be dwindling as growth rate slows. But new trouble is brewing in Chesapeake Bay where blue cat populations are presently exploding in tributaries, and a recent study by Virginia Institute of Marine Science reveals the salt-tolerant blue catfish may be impacting blue crab, blueback herring, and menhaden populations.
While blue cats don't appear to be as harmful as fish-gulping flatheads, serious conservation issues are surfacing. Throughout their range, the blue cat is known to feed on freshwater mussels. In some systems, they are consuming abundant non-native Asiatic clams (Corbicula) and troublesome non-native zebra mussels. This is a good thing. Unfortunately, native freshwater mussels are, as a group, the most endangered animals in North America, and blue cats don't appear to discriminate between "good" mussels and "bad" mussels. An interesting anecdote suggests blue catfish may preferentially feed on mussels. In Virginia's Mattaponi River, blue catfish growth slowed when mussels were no longer consumed. Virginia is keeping a close watch on freshwater mussels.
Flathead Catfish Maintenance Control — Flathead catfish were introduced into the Satilla River, Georgia, in the mid-1990s. Electrofishing of a 79-mile reach began in 1996. Six hundred and thirty-six hours of electrofishing during 1996 to 2006 (average 58 hours per year) removed 12,020 flatheads weighing 32,661 pounds. Despite this harvest, electrofishing catch rate measured as both numbers and weight kept increasing, indicating the newly established flathead population was expanding and removal wasn't keeping up. Electrofishing efforts were more than tripled beginning in 2007. From 2007 to 2009, catch rate sharply declined from 126 pounds per hour in 2007 to 44 pounds per hour in 2009, and the average size of fish removed declined from 5.8 to 1.3 pounds.
Populations fluctuate with environmental conditions, but it's apparent that flatheads can be controlled if a river is small enough and there is enough money and manpower available. That's good news. But's there's bad news, too. With the population held below carrying capacity, flathead growth rates have remained high and there is evidence, although sample sizes are limited at this time, that the remaining flatheads may be maturing at a smaller size. Simple reasoning warns that early maturity plus fast growth equals a population explosion if harvest effort stops.
Response of Native Fishes — In the Altamaha River, where flatheads are not removed but the population appears to have stabilized at a relatively low level, the redbreast sunfish population has rebounded. Unfortunately bullhead (brown, snail, and yellow bullheads) populations that declined sharply during the flathead expansion remain suppressed despite environmental conditions — high water and floodplain inundation — favorable for redbreast sunfish and bullheads.
In the Satilla River, electrofishing catch rates of redbreast sunfish decreased from an average of 125 fish/hour before flathead introduction (1991 to 1995) to 54 fish/hour after flatheads were established (1996 to 2007). During years of flathead catfish removal, redbreast sunfish catch rates fluctuated between 73 and 207 fish/hour. Anglers now are reporting impressive strings of redbreasts. Bullhead populations have fluctuated but averaged 14 fish per hour and are not trending down. As in the Satilla, river conditions have been especially favorable for redbreast sunfish and bullhead growth and survival.
Redbreast sunfish and native bullhead populations in North Carolina rivers remain depressed since flatheads invaded. Formerly abundant channel and white catfish remain rare in Virginia's tidal rivers where both blue and flathead catfish have become established.
The Real Problem: How to Manage
Fishery managers in eastern states where blue and flathead catfish have been introduced are in a significant predicament. All state fishery agencies have a similar mission: provide fishing opportunities for anglers while conserving fishery resources. If all they had to do was conserve, their decision would be easy: get rid of non-native catfish. Easy to say, virtually impossible to do. But even if eradication were possible, fishing license sales pay the bills, and managers truly enjoy providing satisfying fishing opportunities. So any actions must consider what anglers want or, more realistically, what they are willing to accept.
Fishery management attitudes have changed and the knowledge base has expanded greatly. Veteran Virginia Game and Inland Fisheries biologist Bob Greenlee stated, "While blue catfish introductions in the 1970s and 1980s were sanctioned by our agency, we would not consider doing the same today." I think most agencies agree, but self-centered and unknowing anglers created many of these populations. One effort all agencies support is educating anglers to stop spreading invasive predators.
The reality is these invading blue and flathead catfish are now in East Coast and eastern Gulf of Mexico rivers. Populations appear to go through an expansion phase and then stabilize at a lower level, but they are not going away. Flatheads have decimated a couple of native fisheries, but it appears that at least the redbreast sunfish can rebound, especially when the flatheads are aggressively harvested.
A significant step would be to encourage development of commercial fisheries, but consumption advisories in most rivers on the Atlantic coast may be a deal breaker. Tournaments may offer some assistance, but kill tournaments are a thing of the past, and catfish tournaments haven't taken hold in coastal rivers. So it really comes down to expending a lot of resources to sustain traditional fisheries or spend nothing, get an "F" in fishery conservation, and let a new fishery develop while the population stabilizes at a lower and less destructive level.
The situation doesn't seem as bad for blue catfish. Although their effects on channel and white catfish have been severe in one Virginia tidal river, they may not be a problem in all systems they have invaded, and some significant fisheries have developed. Nevertheless, regulations that encourage greater abundance of trophy-size fish may be desirable in shad-filled reservoirs but should be approached cautiously in rivers. However, assessing the effects of invasive catfish must look beyond other sportfish. Potential impacts on freshwater mussels in inland rivers and blue crabs and multiple forage fish species in Chesapeake Bay are rightfully significant concerns. –
*Dr. Hal Schramm, Starkville, Mississippi, is an avid angler, fishery biologist, and freelance writer. He frequently contributes to In-Fisherman publications on science topics.