Blue catfish boom threatens region’s river ecosystems
Predator accounts for 75 percent of all fish biomass in some places
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When a 102-pound, 4-ounce blue catfish was caught on the James River south of Richmond in May 2009, it took two men to land the behemoth. It was the largest blue catfish ever landed in a Bay tributary.
But it's a record that may not stand for long.
Blue catfish populations are booming around the Chesapeake. Overall numbers and average sizes of the predators continue to increase in the James, the Potomac and likely in several Maryland tributaries.
The lower James in particular has become nationally recognized for its production of trophy-size blue catfish, which support a multimillion dollar recreational fishery. Several guides work full time taking anglers to hot spots.
"People are coming from all around the country to fish for blue catfish in the James River," said Bob Greenlee, a fisheries biologist with the Virginia Department of Game and Inland Fisheries. "Their population is still continuing to increase."
Not a single blue catfish was present in the Bay watershed just four decades ago. Today, scientists say they account for 75 percent of all fish biomass in some places.
While electro-fishing in the Rappahannock River, Greenlee and his four-man survey crew have scooped as many as 6,600 fish per hour out of the river using their 16-inch dip nets.
"It is just unbelievable," Greenlee said. "You have to scratch your head and wonder exactly what is going on out there and what the ramifications are for other resources."
That has some scientists and fishery managers worried. The large blue catfish population, they believe, may add to the woes facing native fish such as American shad and river herring, whose populations are near all-time lows.
This month, the Atlantic States Marine Fisheries Commission is expected to approve a resolution supporting efforts to control blue catfish populations in the Bay watershed.
The Bay Program's Sustainable Fisheries Goal Implementation Team, which includes state and federal fishery managers, scientists and others, has been grappling with the issue and hopes to make recommendations for blue catfish management, perhaps this summer.
Blue catfish are the largest catfish species in the United States. They can live to be 20 years old, weigh more than 100 pounds and grow to lengths of more than 5 feet. They are native to the Mississippi River basin, but have been introduced to many other river systems over the years.
One of those systems was the James, where the state Department of Game and Inland Fisheries stocked around 300,000 small catfish in 1974. More stockings continued over the several years, expanding to the Rappahannock and later to the Mattaponi.
That was not unusual. Like kids turning goldfish loose in a local pond, fisheries managers have been moving fish to new areas for more than a century - especially freshwater species. "The history of freshwater fisheries management is like Johnny Appleseed with fish," Greenlee said.
Largemouth bass, smallmouth bass, channel catfish, flathead catfish, common carp, bluegill and brown trout are only some of the common nonnative species that dominate freshwater fisheries in the Bay watershed. Without introductions, "freshwater sportfishing wouldn't be much of a sport or viable industry," said Don Cosden, director of inland fisheries for the Maryland Department of Natural Resources.
Some popular nonnatives such as largemouth bass and rainbow trout continue to be reared in hatcheries and stocked around the Bay watershed.
The blue catfish expansion, though, has been rapid. They are now established in all of Virginia's tidal tributaries, and have colonized and are rapidly expanding in the Potomac. In Maryland, they have also been found in the Patuxent and Nanticoke rivers, as well as in the Upper Bay, including the mouth of the Susquehanna. Biologists say they have had reports of blue catfish in the Choptank River as well.
Populations are centered in the tidal-fresh portions of tributaries, where rivers are wide and deep, but their range has been steadily expanding. According to literature, blue catfish live in salinities of up to 12 parts per thousand. But in this region, they are found in water as salty as 14 parts per thousand, according to Greg Garman, director of the Virginia Commonwealth University Center for Environmental Studies. They may move into even higher salinity waters as populations continue to grow, some believe.
"I can't see why they wouldn't be in the Bay proper, well down the Bay," Cosden said.
The blue catfish, according to Garman, is not just a new species - it's an "apex" predator that rules at the top of food webs - like polar bears or Bengal tigers - and control abundance of species at lower layers, or trophic levels, of the web. But for the Bay's tidal fresh rivers, Garman added, "this isn't just at the top of the food chain, this is a whole new trophic level."
While some large predators such as striped bass visited those areas during spring spawning runs, tidal fresh rivers historically were not inhabited by large numbers of year-round predators. Instead, those areas were dominated by large numbers of smaller resident fish, as well as many migratory species such as American shad, river herring, hickory shad and other species that would either pass through on spawning runs, or use those areas to release eggs each spring.
Over the years, other predators have been introduced into those areas such as largemouth bass. But none are so large or numerous as blue catfish.
Using hydro-acoustic monitoring equipment near Turkey Point on the James River, Garman and colleagues once identified 2,200 "targets" more than a foot long in the water column of an area about the size of an Olympic swimming pool. It turned out that about 99 percent of those "targets" were blue catfish. "It is hard to imagine the densities of blue catfish," Garman said. "Particularly in the James and Rappahannock."
He and others worry that other species are becoming a moving smorgasbord. "The blue catfish is an opportunistic predator," Garman said. "It will eat whatever swims in front of it," he added, as long as it fits in its mouth.
Young blue catfish forage along the bottom for their first few years, eating clams, crustaceans and other bottom dwellers. As they get larger, their appetites expand to include fish, but they also eat crabs, insects, fish or almost anything else in the river. Gizzard shad, a common nonmigratory fish, seems to be a popular food, and it is commonly used for bait by anglers looking for big blue catfish.
Scientists believe that blue catfish are outcompeting native white catfish, whose numbers have declined in rivers as blue catfish increase. Some believe that the channel catfish, a nonnative introduced more than a century ago which has since become a popular recreational species, may also be declining in some areas because of blue catfish competition.
In the Mattaponi River, Greenlee said it appears likely that large numbers of blue catfish have dramatically reduced the freshwater mussel populations.
But the main concerns are focused on American shad and river herring, which include blueback herring and alewife. Massive numbers of those fish once migrated up freshwater rivers each spring to spawn, but their populations are now at all-time lows.
Tens of millions of dollars have been poured into stocking programs and fish passage construction to bolster populations of American shad, which once supported the largest commercial fishery in the Bay. Now, some worry, much of the spring spawning run may simply end up in the bellies of blue catfish.
Scientists also worry blue catfish could be eating other fish of conservation concern, including the Atlantic sturgeon, which has been recommended for federal listing as an endangered species, and American eels, whose populations are also thought to be near record lows.
Proving that is difficult. Blue catfish have rapid digestive systems, so only fish consumed within the past several hours may be found inside. And because numbers of river herring and American shad are relatively low compared to populations of nonmigratory gizzard shad and other species, the odds of finding them in a fish gut are low. "We don't know for sure," Cosden said. "We are theorizing it could be an issue."
Stable isotope analyses conducted by Garman and others a decade ago, which are used to study how carbon moves through ecosystems, indicated that carbon from marine systems was helping to fuel blue catfish growth. The most likely source of marine carbon in tidal fresh waters, he said, is migratory fish.
Greenlee agreed that blue catfish are almost certainly eating some shad and herring, but questioned whether it was a major factor in the shad's and herring's declines. He said a relatively small number of blue catfish grow large enough to eat a female shad that is ready to spawn.
And, he noted, shad and herring populations are in decline all along the East Coast - not just in rivers with blue catfish populations. "If you began to see recoveries in other populations with declines continuing here, you might point to predation," Greenlee said.
Further, he said, hickory shad numbers have rebounded from low levels over the last decade despite increased populations of blue catfish.
He suggested factors outside the Bay were at play. A number of fishery biologists have suggested that American shad and river herring caught in the bycatch of ocean fisheries may be hindering recoveries along the coast.
Cosden agreed that the current condition of American shad and river herring stocks were likely driven by factors other than blue catfish. Nonetheless, he added, with populations at such low levels, growing blue catfish numbers could hinder efforts to restore those species. "Our fear is that blue catfish are one more straw," he said.
But figuring out what to do about them is difficult.
Some have suggested that anglers who catch large blue catfish should be encouraged to kill, rather than release, them. Greenlee said that runs counter to the ethics of trophy fishermen. "If you come into a tournament and you have a dead catfish, you are basically ostracized for life." Besides, he added, "a few recreational anglers out there killing blue catfish might make you feel good. But is it going to impact the population? I don't think so."
In fact, only a very small number of blue catfish grow anywhere near trophy size; most are 2 feet or less.
It's possible that culling the numbers of smaller fish could actually benefit the trophy fishery. While blue catfish populations continue to grow in places such as the Rappahannock and York rivers, Greenlee said the number of giant fish appears to be decreasing - a sign that the density of the population is limiting their growth.
But there is no obvious way to control such a large population. Greenlee said the commercial catch of blue catfish, which targets fish less than 32 inches, saturates market demand at about 2 million pounds - a catch level that has failed to curtail population growth.
Marketability is also limited by consumption advisories. Tidal fresh segments of rivers tend to be located near large cities - that's as far as ships could navigate - and often have relatively high levels of toxics in the sediment. Because of their long lives, which begin as bottom feeders, blue catfish can accumulate harmful levels of toxins. On the James River, the Virginia Department of Health recommends no consumption of blue catfish longer than 32 inches, and no more than two meals a month of smaller blue catfish.
Garman said it might be possible to identify particularly valuable habitats for shad and herring, and work to control populations with intense electro-fishing programs. But such efforts would be expensive and, once started, would have to continue indefinitely to be effective, he added.
Also, any action or regulation perceived as harmful to blue catfish could stir conflict among angler groups. American and hickory shad have been prized by many recreational anglers for years, but only weigh a few pounds. Anglers seeking large trophy fish, like blue catfish, represent an increasingly popular part of the recreational fishery. As the website of Catfish Nation, which organizes catfish trophy tournaments, put it: "Why fish for bait when you can catch a beast?"
Still, most agree that raising awareness of potential impacts might at least help deter fishermen from intentionally moving blue catfish into new tributaries. "There is good reason to believe that these fish that showed up in the Nanticoke and the Patuxent didn't swim there," Cosden noted.
Moving fish, he said, has the potential to affect populations prized by other anglers, whether it's shad, white perch, yellow perch or something else. "Now you are impacting someone else's sport, it's not just us tree-huggers saying you shouldn't do this," Cosden said.
The DNR has been wrestling with whether to recognize blue catfish as a trophy fish out of concern that it legitimizes and promotes moving the fish into new systems. Right now, it does recognize blue catfish catch records, but Cosden said that will likely change in the future.
Nonetheless, he and others acknowledge that blue catfish populations are here to stay.
Indeed, while they may not be native to the Bay, they are ideally adapted to the nutrient-enriched estuary as it exists today, Greenlee said. Those nutrients have helped fuel growth of huge numbers of gizzard shad and other prey fish in tidal fresh areas of rivers that support larger predator populations.
"We have wholesale changes that have gone on out there," Greenlee said. "Blue catfish are not a cause. They are a symptom. Blue catfish thrive there because of the eutrophic systems that we've created. They are wildly successful in these systems."
- Category: Fisheries
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