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'Rock snot' invasive algae threatens Jackson River
BY CHARLES GARRATT • STAFF WRITER
 | | Fisheries biologist Paul Bugas shows how didymo, also called rock snot, is covering rocks in the tail waters of the Jackson River below Gathright Dam. The invasive algae covers the rocks to a depth of one-half inch or more, preventing the normal macroinvertebrates that trout feed on from finding food. The algae can also impact use of the river for recreation and could seriously reduce the trout population. (Recorder photo by Charles Garratt) |
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GATHRIGHT DAM - State fisheries biologists are concerned about the impact the invasive algae known as "didymo" or "rock snot" discovered in the tail waters of the Jackson River below Gathright Dam three years ago may have on the trout population in the river.
The rapidly growing algae have spread across the entire river just below the dam and extend down stream past Natural Well. A native of northern latitudes in North America, Europe and Asia, didymo has been expanding its range in recent years, often decimating trout habitat and limiting recreational use of normally pristine waters.
Didymo is a single-cell diatom, which can be spread in a single drop of water. The algae can grow rapidly and produce a tough stalk, which does not break down easily. After a large bloom, the bottom of an infected river or stream can appear to be covered with wet toilet paper.
Department of Game and Inland Fisheries biologist Paul Bugas said didymo has spread rapidly since found in the Jackson River in 2004. In the area near the dam, the algae covers most rocks from shore to shore and is found in high concentrations down to Natural Well, he said.
The brownish growth covers rocks to a half-inch or more, choking off the feeding and hiding places of many of the species of macroinvertebrates (visible animals without backbones) native to the river, Bugas said.
Last Friday, Bugas lifted a didymo covered rock from the Jackson and pulled back the mat of algae. Pointing to the nooks and crevices in the rock, he said a flat-headed mayfly could have lived under the rock and crawled around on it searching the crevices for food. But with the thick covering of rock snot, there is no place for the mayfly and similar creatures to live and feed.
That's could be bad news for the trout that live and breed in the Jackson. Mayflies and other bottom-dwelling animals native to the river are a primary food source for rainbow and brown trout.
Bugas and fisheries technician Jason Hallacher were on the river Friday to sample the section below the dam to gauge the health of the trout population. "In the good ole days we'd get 50 to 100 trout, mostly rainbows" in the section of the river between the dam and the first set of rapids. The rainbows, he said, could reach 16 inches and they would net an occasional brown trout 18 to 20 inches.
The sampling on Friday was cut short by an equipment failure but so far Bugas feels the trout population "looks as good as ever." DGIF has been sampling annually at six stations on the Jackson for many years and has good records to track any changes in the fish population.
While didymo is spreading across the river bottom, Bugas points to areas of small gravel the size of a dinner plate that can still be used by breeding trout.
The Jackson River below the Gathright Dam has not been stocked since 1997. The habitat is good enough to support reproducing populations of rainbow and brown trout. The Corps of Engineers operates the dam and releases water from different levels of Lake Moomaw to maintain the river at 60 degrees or less below the dam.
The dam and lake allowed the Jackson to become a world-class trout fishery, said Bugas, and he'd hate to see it take a hit from didymo. The algae are non-toxic, he noted, and while it looks slimy, it actually feels more like wet carpet or cotton wool.
Bugas hopes that if it takes over the colder part of the river near the dam, downstream where the water is warmer will stay open. Hopefully the tributaries and enough of the river will stay clear of the pest to allow the trout to continue to breed and feed, he said.
Didymo became an international problem when it was discovered in New Zealand in 2004, the first known infestation in the Southern Hemisphere. Since then it has spread to a number of pristine rivers in that country.
According to New Zealand Biosecurity, didymo came from North American, most likely on felt-soled waders, because didymo can last on them for months if they stay damp. New Zealand has taken drastic steps to protect fisheries, including banning fishing in high country spawning grounds and distributing spray bottles for use in cleaning equipment.
The impact of didymo on New Zealand could reach $30 million (NZ) per year, according to Biosecurity New Zealand.
In Virginia, the impact of didymo has not been calculated. It was found in the tail waters of the Smith and Jackson rivers last year. This year it has also been found in the Pound River, according to Bugas.
DGIF is working with the U.S. Forest Service, the Department of Conservation and Recreation and Trout Unlimited to prepare a large-scale education program to alert anglers and recreational boaters on the dangers of spreading didymo and how to clean boats, trailers and gear.
Large posters are being prepared for public access points, gear shops, marinas and other locations. A laminated fact card will be distributed as widely as possible so people will have the information on how to clean and disinfect gear in a waterproof, readily available form.
Even as Bugas talked about the education and awareness program, the difficulty of stopping the spread became obvious. A small amount of didymo clung tenaciously under his fingernail even after he wiped his hands clean.
Felt bottom waders are blamed for spreading didymo since the tiny cells can live a long time in the damp surface. The bottom of boats, trailer tires, clothing and anything else that gets in the water can carry the algae to a new location. As Bugas talked about the different ways didymo can be spread, he realized dogs could also spread the pest in thick wet fur.
"We are a victim of our own folly," Bugas said. Man created the ideal conditions for the algae when he used dams to create cold-water fisheries. Thanks to better equipment and faster travel, Bugas said an angler can fish waters in high country in British Columbia, jump a plane to Montana or Virginia or New Zealand, and be fishing in a new river or stream before the waders have a chance to dry, taking didymo and who knows what else along for the ride.
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