Smallmouth surge: Nonnative fish thrive in drought, threaten native species

COLORADO DIVISION OF WILDLIFE—Andrea Sponseller, left, Jeffrey Behncke, center, and Andrew Nordick of the Colorado Division of Wildlife conduct an electrofishing operation in the mouth of a tributary stream along the Yampa River near Maybell. Nonnative species are plucked from the surface after all the fish in an area are stunned.

As drought conditions settle onto the Grand Valley, its human residents are not the only ones likely to feel the squeeze. As in other recent droughts, the several species of endangered fish that share our rivers, living in the water we use in our fields and cities, will face increased difficulty trying to spawn and increased threats from nonnative predatory fish.

Unlike during the previous major drought, however, new and better tools may be available to help keep those fish swimming.

When river levels dipped to dangerously low levels during the drought of 2002, the Colorado pikeminnow suddenly faced an existential crisis as shallower water made it more difficult to spawn. The razorback sucker, humpback chub and bonytail, all endangered fish native to the upper Colorado River, found themselves in similar situations.

Complicating their predicament, the same conditions that harm native fish benefit nonnative species such as smallmouth bass, according to biologists. These nonnatives tend to thrive in drought years, when warmer water temperatures and less competition from native species allow for a much more successful spawning season.

They also tend to prey on the young of the native species.

In past drought years, endangered fish like the pikeminnow “just didn’t have the habitat available to spawn and even if they did there was a large population of nonnatives that wiped them out,” said Dale Ryden, a fish biologist with the U.S. Fish and Wildlife Service office in Grand Junction.

Tom Chart, director of the Upper Colorado River Endangered Fish Recovery Program, said his program is “really concerned” about smallmouth bass this year. “They went crazy in 2002,” he said. “We’re sure (smallmouth) are going to have a good reproductive year this year.”

The low snowpack, early spring and fast runoff have led many to predict a drought at least on par with 2002.

“These years really favor the young of the nonnative fish,” Ryden said. If a big flow does not follow in the next couple years “to blow them out of the water,” the nonnatives will become adults and eventually develop into a critical mass that is here to stay, Ryden said.

That is what happened post-2002. The estimated smallmouth populations in the Colorado and Gunnison rivers exploded following that drought year — even as the total number of fish in the rivers dropped. U.S. Fish and Wildlife Service studies show smallmouth bass increasing from less than 1 percent of the total fish in the Colorado and Gunnison in 1999 to over 50 percent in 2004.

“2002 was a huge year for them and they’ve been problem ever since,” said Ryden.

Removing fish

He said a repeat of that smallmouth explosion is feared for this year, though it could also be a different nonnative species that takes the favorable conditions and runs with them this time around. Smallmouth are the most common nonnative fish around Grand Junction. Northern pike are prevalent around Craig, and walleye in the Green River.

Either way, biologists and wildlife officials are bracing for impacts on local endangered fish.

Part of the response to this onslaught will be reactive. Boats will go out to temporarily stun the fish within a radius in a process called “electrofishing.” Nonnative species like smallmouth or northern pike will be picked out from the fish that float to the surface and either euthanized or, in some cases, moved to fishing ponds.

The other is a more proactive method: ensuring enough water remains in the rivers so that endangered fish can spawn and nonnative predatory fish will not take over in the first place.

Despite having evolved to deal with drought, native fish now experience a different type of drought than in the past.

The Colorado River used to be a “very flashy system” with high peak spring flows and low summer flows, said Ryden. Now, the heavy regulation of the flows for cities, irrigation and other uses cuts off the extreme highs and, to a degree, lows, allowing for a much different, more steady river in which nonnative fish can get more of a foothold.

Moreover, although adult native fish can still survive droughts such as this year’s, their spawning is inhibited, meaning that even the hardiest of species would have trouble surviving an extended drought period. “It’s when we get into five, six, seven years like this, that it gets to be a problem,” Ryden said.

Flows, river users

The Recovery Program has been making flow recommendations since 1988 on how much water they think endangered fish in the Upper Colorado will need to be able to spawn and, eventually, recover.

Ideally, Chart said, around 800 cubic feet per second would be flowing during a dry year through the “15-mile reach,” the particularly vulnerable stretch of the Colorado leading up to where the river meets the Gunnison and in which endangered fish, especially the pikeminnow, can be found.

“But we were below 100 CFS in 2002,” he said, “and we may very well get there again this year.”

Part of his job is to work collaboratively with water users to try to find ways to meet the fishes’ needs. His team requests excess water, if it exists, to be released from reservoirs to benefit the fish, but it does not seem likely that any excess will be available this year.

So, rather than trying to advance endangered fishes’ recoveries, their goal this year will be less ambitious.

“We will just be trying to mitigate the drought’s impacts,” Chart said. “In a year like this, we’re not going to meet those minimum flow recommendations. The main concern this year is over an explosion of nonnative species.”

They will have new tools to help them with that work, at least.

In 2002, conservationists and water users realized there was no expeditious way for Coloradans with more water than they planned on using to temporarily donate those water rights to preserving riparian wildlife and habitat.

In response, an Instream Flow Program was set up in 2003 to do just that. The Colorado Water Trust is utilizing this tool for the first time this year, compensating water users “at fair market value” for putting water back into Colorado’s rivers and streams on a short-term basis.

This will avoid the hassle of going through water courts and “can be implemented much more quickly,” according to the trust’s executive director, Amy Beatie.

Water leases

She has been trying to explain the program to potential participants this month, including at a forum in the Roaring Fork Valley late last week.

“Lots of people seemed to have interest in the program,” Beatie said, though she noted they will not know how many participants they will have until the after the first round of applications are submitted on Friday.

Both Chart and Ryden had not yet had the time to dive into the complexities of the short-term water leasing program, but Chart said he thought it would have some impact.

He also pointed to another development spawned from the 2002 drought. Since then, they have learned a lot about how to more effectively and efficiently remove nonnative species before they can have serious impacts, both in terms of technique and timing.

Ryden, who helps coordinate that nonnative removal work around the Grand Junction area, expects this year’s efforts to begin a bit earlier than normal, possibly in early July.


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