Some scientists may be rethinking the idea that anglers spread didymo from stream to stream on the soles of their shoes, but don’t expect to see any “Never Mind” signs along creeks anytime soon.
Fishery managers and environmental advocates still say felt soles are a bad idea. For one thing, they say, even if the “rock snot” alga is native to the whole country, that doesn’t mean it’s present in each and every stream, and introductions may still be possible.
And besides, didymo is only one of the aquatic nuisances that thrive in damp felt soles. There may even be some we don’t know about yet.
“To me, the list of potential cold-water aquatic invasive species changes yearly,” said Dave Kumlien, director of Trout Unlimited’s national Aquatic Invasive Species Program. Kumlien ran a fly shop in Bozeman, Mont.. for 20 years and has been executive director of the Whirling Disease Foundation.
“We have no idea what the next threat will be, where it will come from, what the vectors for movement will be or what the impact will be,” he said. “To abandon or change our approach on clean angling is sort of myopic. We’ve gotten some people to care about their equipment and to be aware of the risks of moving plants and organisms.”
Soon after didymo blooms began appearing in blue-ribbon trout streams around the country in the mid-2000s, scientists and conservation departments said the likely reason was that anglers were unknowingly moving a new variant of the alga from stream to stream in the damp felt of their wading shoes.
The most prominent advocate of the idea was Max Bothwell of Environment Canada, author of a 2009 article in Fisheries magazine 2009 titled “On the Boots of Fishermen: The History of Didymo Blooms on Vancouver Island, British Columbia.”
The theory led several states to ban felt soles, and led the fishing tackle industry to all but eliminate them from their inventories, offering instead rubber-soled shoes designed to grip underwater rocks as effectively as felt.
But this year, Bothwell said further research has led him to change his mind. Environmental changes were causing the blooms, he said. Fly-fishers weren’t the Trojan horses of didymo after all.
Bothwell’s findings surprised the International Didymo Conference in Rhode Island in March. Trout Unlimited was a sponsor of the conference, and Kumlien was there.
“It was sort of gospel that anglers were moving it around, so that was a startling bit of news that he presented,” Kumlien said.
The New York Department of Environmental Conservation was on board with the felt soles theory of didymo and has posted streamside warning signs urging anglers to clean, check and dry their gear, especially their shoes.
The DEC plans no immediate change in its approach, said spokeswoman Lori Severino.
“Didymo cells, along with other living organisms, can potentially live in the moist felt of waders,” Severino said. “Therefore, it is still important to continue outreach and education on the importance to clean, dry, and when necessary, treat equipment between different water bodies so that they do not serve as a potential vector for spreading unwanted organisms between waters.”
Didymo may be native to all of North America, but Bothwell did say it may have been introduced to New Zealand, where it had never been found before 2004 — and where didymo blooms have caused significant damage to high-quality trout streams since.
So perhaps it can be moved around — and that’s why it may still be correct to think of didymo as a potential intruder, said Charles R. O’Neill Jr., coordinator for invasive species programs at Cornell University Cooperative Extension.
“It is possible that didymo is not present in all aquatic ecosystems in North America, but is, instead, being transported into those waterways by some form of human intervention,” O’Neill said. “In this case, an ecosystem-to-ecosystem introduction would fit part of the definition of an invasive species.”
Bottom line: consider switching from felt to rubber, and continue to check, clean and dry.