Rock Snot

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I hope it isn't coming to your fishing grounds:

Debate rages on ‘rock snot’
Tiny diatom causing big headaches for rivers worldwide

Sunday, November 13, 2005

Coming soon to a river near you.

Rock snot.

OK, so that doesn’t carry the fear factor of some other worldly creature. Nevertheless, didymosphenia geminata, commonly known as didymo (or rock snot from its slimy appearance) is confounding scientists and frustrating anglers.

Didymo is minute diatom that grows into slick brown algae mats that coat streambeds and river bottoms. If thick enough, the mats of algae threaten underwater bug life.

Once thought to be limited to cold-water lakes in the northern climes, the minute diatom has spread in recent years to such angling corners as Tennessee, Arkansas, Utah and even New Zealand.

It’s been suspected of choking out the insect life in rivers that fish live on. South Dakota blames didymo for a 90 percent decline in brown trout in some waters.

Colorado isn’t immune. First reported in the Fryingpan River in 1975, it’s also found in the Eagle and Gunnison rivers and didymo blooms have been documented at about 40 sites.

“It’s been in the Gunnison River since I’ve been a biologist here,” said Sherman Hebein, senior aquatics biologist for the Colorado Division of Wildlife. “We don’t have any real information on its range or distribution but I suspect it’s in all of our water. If it’s in the Gunnison it’s probably everywhere.”

Veteran angling guide Hank Hotze said he’s seen it in the Gunnison Gorge and below.

“Down the corner past the (Gunnison) Forks we have tons, and the stuff is absolutely a mat,” Hotze said. “This year the North Fork got to 6,000 or 7,000 (cubic feet per second) and the stuff just stayed there.”

A study done by Sarah Spaulding of the U.S. Geological Survey said didymo can blanket river bottoms with mats more than a mile long. As the colonies grow, they look like white to light brown tufts attached to rocks. The colonies eventually smother rock surfaces and trap fine sediment.

The dense mats, which look like toilet paper, exclude the growth of other diatoms, an important source of food for aquatic invertebrates. As a result, a decline in aquatic invertebrates causes a decline in food available for fish.

Hebein cautiously said that it’s unlikely the didymo would spread to where it’s a major concern.

“I would be surprised if we have severe problems with the stuff, but I have seen it coat the bottom of the Gunnison below Crystal Dam quite thoroughly,” he said.

Hebein said the algae likely benefitted from a recent confluence of favorable growing conditions, in part due to the drought that reduced water levels and increased water temperatures.

“Every organism has its preferred temperature, nutrient and light level, and at some time all those things line right up for organisms that have been in the background,” Hebein said. “Occasionally, when these conditions line up, (the organism) multiplies like crazy but when water temperature falls and the photo level changes, the organism kind of dies off and goes back to the way it was.

“I hope that’s what we are seeing with didymo.”

But Hotze isn’t too sure.

“Maybe it’s been there for a while but the interesting coincidence, if you read the research, they started identifying didymo as a problem in Canada in 1988 or ’89 and that’s exactly when this river became a petri dish and we all saw it bloom,” Hotze said. “Guides and everybody started seeing it, and it’s beginning to bother me.”

Hotze said didymo might throw off the delicate balance of Colorado’s prime fishing rivers.

“When (didymo) goes out of balance it covers the rocks and substrate and (eventually) kills the invertebrates,” he said. “If we lose them, we lose the fish.”

The didymo organism hangs from a thin stalk and spreads when broken loose by high water or carried by waders, boots, a boat bottom or even a float tube.

The New Zealand Recreational Canoeing Association warns on its Web site that didymo is “a major problem for kayaking” and “ river users risk a fine of up to $100,000 or five years in jail if they knowingly spread didymo.”

When discovered last year, the New Zealand government considered fighting the algae with bleach or even draining infected waterways.

It’s likely people — anglers and boaters — share in spreading the organism.

It’s doesn’t take much to spread didymo, as little as a drop of water containing one of the diatoms. Prevention, too, is relatively simple.

Washing your waders, boots or boats in a 2 percent bleach solution or allowing your equipment to air dry for several days are effective methods in killing didymo, said Jeff Shearer, aquatic ecologist with the South Dakota Game Fish and Parks.

“These preventative measures may be an inconvenience, but are important for controlling the accidental spread of didymo and other aquatic nuisance species, such as New Zealand mud snails or whirling disease,” Shearer said.

Hebein, the Western Slope’s top aquatic biologist, said it may be that didymo will subside or disappear when the regular weather cycles reappear and put more water in the rivers.

“I think it’s one of those transient things that will go away,” said Hebein.

Hotze, though, rolled his eyes at the news.

“I think it’s really bad news,” he said. “I see it more as the ‘what if?’

“If all things are perfect, then what happens?”