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Courtesy photo
Didymo ("rock snot") is a major problem in New Zealand, where it has choked some streams, as shown in this photo from several years ago. Fears of similar disasters have prodded concern in the U.S.
Monday, November 21, 2011

Invasive spillover in wake of Irene

In one of the strangest problems arising from this year’s extreme weather, flooding from Tropical Storm Irene has endangered hundreds of thousands of hatchery fish in Vermont due to possible contamination by the invasive algae “rock snot,” which is also a problem in the New Hampshire headwaters of the Connecticut River.

About 3,000 salmon from the federal White River Fish Hatchery in Bethel, Vt., some as large as 5 pounds, will be given to Native American tribes throughout the Northeast to be eaten, some as part of tribal ceremonies. The salmon were previously going to be stocked for fishing, mostly in western Massachusetts lakes as part of an ice-fishing program.

Another 3,400 smaller salmon will be released into parts of the Connecticut River basin that are already contaminated with the algae, officially called didymo, short for the species name Didymosphenia geminata.

As part of the devastation wrought by Irene, the hatchery was flooded by waters of the White River, which has had didymo for a couple of years. Parts of the hatchery were buried by 8 feet of mud, and it was unreachable for several days.

Officials fear the flooding might have carried microscopic bits of the algae into the holding tanks, and that these might be carried on salmon to new rivers. Since didymo thrives in cold, fast-running, clear water – just the sort of place where the salmon are stocked – they didn’t want to release the fish into places where the algae hasn’t been found.

It’s not clear what will happen to about 430,000 trout that were going to be stocked in Lake Ontario and Lake Erie as part of a lake trout restoration program. They are currently undergoing tests to determine whether they, and the water they are carried in, can be certified as being free of didymo.

“I just sent them samples from the Connecticut River to double-check the method, to make sure they would see the didymo that is here,” said Amy Smagula, exotic aquatic species coordinator for the state Department of Environmental Services.

“There was nothing definitive that clearly showed that didymo had gotten in (the hatchery) – they couldn’t find any DNA or other evidence,” she said. But Smagula agreed that caution was warranted.

Like many algae, didymo populations can explode overnight, leading to huge mats of material that can coat rocks and choke out much other life from small rivers.

It has spread around the world – it is a particular problem in New Zealand – and is found in a dozen places throughout the United States. It showed up in the Connecticut River two years ago, but so far has not spread very far in New Hampshire.

Didymo is one of a number of aquatic invasive species that has raised concerns in New Hampshire waters in the past two decades. Most, such as milfoil or water chestnuts, are prevalent in southern New Hampshire, but didymo seems unlikely to spread here from the North Country, partly because of the chemical composition of the water caused by soils, noticeable in the way local brooks are is often cola-colored from high tannin levels.

“They like places where you don’t usually expect to see a bloom – clear waters, lower nutrients. I don’t think a lot of our southern tributaries are concerns because they’re too colored,” Smagula said.

Didymo is thought to spread on equipment and clothing used by people fishing. This has led to a major controversy over wading boots that have soles made of felt. Fishermen like these soles because they are not slippery, but it’s very difficult to clean felt, which makes them more likely to spread the microscopic diatoms of didymo.

Vermont is one of several states that has banned felt-soled boots, but New Hampshire lawmakers have declined to follow suit.

Didymo has also been found in Hall Stream, Mohawk Brook and Indian Stream in New Hampshire.

Smagula said she has followed up reports from the Androscoggin and Baker rivers, “but we have checked extensively, and haven’t found any signs.”

She said people often mistakenly identify green filamented algae.

Some of the large salmon removed from the hatchery will be given to a Micmac band around Presque Isle, Maine, where they will be used as part of a ceremony to mark the 20-year anniversary of the tribe’s recognition by the federal government, according to press reports.

About 1,000 people are expected for the celebration. The salmon will be served along with moose, fiddlehead ferns and other traditional foods.

David Brooks can be reached at 594-6531 or dbrooks@nashuatelegraph.com.