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Colorado's public lands are faced with new challenges but water and land management depend on working together. Read about the relationship between water and land in Colorado and how Coloradans are converging to restore Colorado's public lands in the Spring 2018 issue of Headwaters magazine.

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Water Education Colorado

What a Nuisance

Story by Lori Ozzello | Photographs by Kevin Moloney

Whirling disease seemed unbeatable.

The disease stumped aquatic researchers in the mid 1990s and decimated the state's wild rainbow trout population. It tolerated extreme temperatures and could lie dormant in silt for years. Biologists devised ways to rid state hatcheries of the invasive disease, but they struggled to somehow inoculate or protect the wild trout.

From the tiny worms that cause whirling disease in fish and deformities in frogs to New Zealand mudsnails that crowd out native mollusks to cheatgrass that causes wildfires and further fosters itself, nuisance species pose enormous biological and economical problems in Colorado and around the world.

One Cornell University estimate puts the annual cost at $137 billion. A Utah study puts an average pricetag for invaders at $1 million per species per year, but no one knows for certain what the amount really is, or how many invaders there are.

Cornell ecologist David Pimentel ‘is the only one to try to put a number to it,’ says Tom Stohlgren, branch chief at the U.S. Geological Survey's Fort Collins Science Center. ‘Even if he's off by a factor of two, it's bigger than hurricanes, earthquakes and fires combined.’

Some nonnatives are benign, but others push native species out, kill or sicken wildlife, destroy habitat and affect water.

‘Forecasting the weather is interesting, but we really need to forecast invasions,’ says Stolgren. ‘We're working on it, developing computer and spatial models, from where (invasive species) are now to their next step. We may have to take a more humble approach and stop these things, maybe one step at a time.’

Several state and federal organizations as well as more specialized groups are engaged in what may be a Sisyphean task: trying to keep nuisance species out; keeping tabs on the myriad ones already in Colorado; and trying to eliminate or contain the worst of them.

‘We're spreading things around,’ Stohlgren says. ‘Ecology used to be slow. We're kind of one big island now. Trade and transportation increases and it opens the door to sharing plants, animals and pathogens at a must faster rate.’

The Fort Collins group, he says, ‘is trying to be more optimistic and predictive. We want to learn more about early detection. We're treating it like an ecological wild fire. We have a smoke jumper mentality when something new comes into our state, our country or our backyard.’

Expelling the invaders often is next to impossible.

But for the whirling disease warriors, the story took a twist. A few years ago, fisheries researcher George Schisler and his colleagues at the Colorado Division of Wildlife caught an amazing break.

The Colorado researchers were acquainted with a Munich professor also studying whirling disease. They asked him for help. Not far from Munich, he found a breed of rainbow trout resistant to whirling disease. His discovery, in a Bavarian hatchery, may help restore the state's wild trout population.

‘We're working on developing strains of rainbow trout resistant to whirling disease,’ says Schisler, ‘and we're having quite a bit of success.’

The microscopic parasite that causes whirling disease is one of countless species that hitchhike to the state. The nonnatives arrive via shipments of seafood; on equipment and boats used in different waterways; and acts intended as kindness. Some are deliberately imported for use in agriculture or landscaping but escape into the wild.
‘Until the last few years, we hadn't given a lot of thought to what we could spread around,’ says Vicky Milano, a Colorado Division of Wildlife fish pathologist. ‘Anyone using water is a vector.’

People's increased mobility and global trade expansion make it easy to share an unprecedented number of plants, animals and pathogens, says Stohlgren. He supervises a staff of scientists who are federal employees, contractors and graduate students.

‘We've broken down the barrier,’ says Stohlgren. ‘Darwin used to go out in a boat to look for biodiversity. Now it comes to us. Every computer is a portal. … We move things around. We shared things in estuaries by moving seafood. We have diddled.’

Sometimes, it was unknowingly.

Whirling disease was first detected in the eastern United States about 50 years ago, traced back to a shipment of live fish from Europe to Pennsylvania. Whirling disease was accidentally introduced to Colorado sometime in the mid 1980s. By the 1990s, the disease had been confirmed in 13 of the state's 15 major waterways, including the Colorado, Gunnison, Rio Grande, South Platte and Arkansas rivers. Although whirling disease can affect other salmonids, the rainbows are most susceptible.

The parasite requires two hosts—trout and tubifex worms, common river bottom dwellers.
According to the DOW, when an infected trout dies and its body decays, a large number of hard spores are released. The spores are ‘hardy, resist freezing and drought and can remain viable for decades.’

‘Think of the tubifex worms as aquatic earthworms,’ says Schisler. ‘As they process the dead fish, they eat the spores, which reproduce in the worms' guts.’

Eventually, the worms rupture, scattering fine spores in the water. The spores, equipped with tiny hooks, latch onto passing fish and work their way into soft cartilage, causing nerve damage, skeletal deformities and death.

The parasite destroyed wild trout populations across the West and baffled researchers like Schisler. Nothing seemed quite able to kill it.

In the turn of events is some irony: Rainbow trout are themselves nonnative and the solution was imported.
Rainbows, a favorite of anglers in Colorado, are native to the West, but not to Colorado. Still, says Milano, ‘We've cultured them.’

Over time, breeds particular to Colorado, its climate and altitude developed. One is known as the Tasmanian rainbow trout.

Anglers elsewhere wanted rainbows and they were shipped out of the western United States to Europe in the late 1800s. Like Colorado's rainbows, they were bred for different purposes once they landed across the pond.

Schisler and other researchers studied whirling disease and shared what they learned. They knew brown trout, native to Europe, are resistant to whirling disease. Otherwise, he says, ‘We didn't have much.’

The Colorado researcher asked an overseas colleague, Mansour El-Matbouli, to look around for rainbow trout strains that showed resistance to whirling disease. The University of Munich biologist found one at the Hofer Hatchery near the southern German city. The catch: The Hofer rainbows had been developed as a food fish, not a wild river trout.

And getting Hofer eggs to Colorado took patience, paperwork and a quarantine. The imported eggs arrived in 2003 and, after more tests, Schisler and his colleagues began to cross breed them with the Tasmanians.

The fish—products of female Hofers and male Tasmanians nurtured in hatcheries—were stocked in 2004 in the Gunnison River. Some survived, and each year since, the survival rates improved. In the intervening years, CDOW stocked the South Platte, Arkansas, Fryingpan, Colorado and Rio Grande rivers with the Tasmanian-Hofer cross. So far, 75 percent of the anglers who've caught them can't detect the difference. The crossbred fish stocked in rivers reverted to wild habits. Schisler says there are indications they've reproduced in the Gunnison. DNA results are pending.

‘We're really doing good things,’ says Schisler. ‘With the wild trout, we're not quite there yet. When we see robust populations again, we'll say we've licked it.’

CDOW also stocked the crossbred fish in reservoirs. They won't reproduce there because rainbows require flowing water to spawn.

‘We don't care if those (reservoir) fish have wild behavior,’ says Schisler. ‘We want people to go out and catch them. What we're finding is the Hofers grow well and they're a great strain. We can produce catchable fish faster.’

Schisler points out water management techniques have a significant impact on whirling disease. Flushing flows, for example, alleviate sediment buildup, destroying mid generation tubifex that thrive in heavy organic silt.

‘We shouldn't look at the resistant strain as a cure all by themselves,’ Schisler says. ‘Water resources have a lot to do with all kinds of things for the fish. Just because there's water doesn't mean it's healthy.’

Stohlgren adds that groups like his are not only studying the invaders, they're trying to forecast species' next steps.

‘We've established an advanced invasive species modeling room,’ he says. ‘It's like a war room. We're developing maps of where Africanized honey bees are going to go because of weather, etc. We're training the next generation.’
New ecologists, he says, will have to know more math and computer science, develop maps and computer models.
Guessing at the future of invasive species, their next move and what to do is a lot like science fiction, he admits.

‘I gave a talk at NASA once,’ Stohlgren says. ‘I told them—we have a Hubble telescope. What we need is a Hubble microscope to look down on earth, tracking species that move and crawl and swim and carry very small organisms.’

Five Easy Steps to Prevent Aquatic Nuisance Species

1. Never release nonnative species into the wild.
2. Never move water, animals or plants from one body of water to another. (Boat hulls and motors should be cleaned after use to prevent the spread of snails and parasites.)
3. Learn to recognize common invaders.
4. Share your knowledge to prevent the spread of nuisance species.
5. Report invasive species. Call (970)842-6308.

CU Researcher Solves Frog Mystery
A University of Colorado researcher helped solve a frog riddle that vexed biologists for a decade. Pieter Johnson says deformed frogs, first discovered in the Great Lakes region in 1997, raised ‘lots of debate’ as their range and frequency increased.

In a National Science Foundation-funded study published in late September, Johnson reported the deformities are a result of nutrient runoff from farming and ranching, which fuel parasitic infections. Johnson believes the findings, which may also have some bearing on whirling disease, are emblematic of other issues likely to arise.
Amphibians are the most threatened group of vertebrates, suffering major declines on every continent because of habitat loss and diseases.

‘The frogs have extra legs or twisted legs,’ says Johnson, an assistant professor of ecology and evolution. ‘Our research has pointed to a flatworm parasite, also known as a fluke.

‘Frogs are used as second, intermediate hosts. From the evolutionary standpoint, deformed frogs are more susceptible to predators. We struggled with parasite abundance. What we finally started to see was that higher nutrient levels stimulate plant and algae growth, fueling higher abundance of the snails, which host more parasites. The snails are well fed and can produce more parasites.’

The major cause is a parasite known as a trematode. It prefers the red-eared radix, an exotic freshwater snail species that, like whirling disease-causing tubifex worms, thrives in silt and tolerates pollution and a range of temperatures. The snails, with plenty to eat, grow faster and get bigger, protecting themselves from predators.

The trematodes' complex life cycle involves three parts: the infectious stage in snails and a cyst stage in frogs. Then, they depend on wading birds to eat infected frogs and spread more parasites through defecation. Johnson says the distribution pattern follows the flyway.

The trematode larvae burrow into tadpoles' limb regions, disrupting normal development. The deformed frogs don't survive long in the wild.

The host radix snails, says Johnson, found in several sites in Denver, are larger than the New Zealand mudsnails causing alarm on the South Platte River.

‘Reducing the (nutrient) runoff is the biggest issue in my opinion,’ says Johnson. ‘The nitrogen and phosphorous in fertilizers cause toxic algae blooms, mosquitoes and possibly whirling disease.’

Nutrient runoff has ‘a broad potential to affect aquatic and human diseases, such as West Nile virus,’ Johnson says. ‘We just don't know how severely.’

To reduce adverse effects, people can apply fertilizer more efficiently, he says, in the proper amounts at the correct time of year. He also advocates buffer zones, such as trees, shrubs and grasses to absorb and filter nutrient runoff before it reaches water bodies.

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