Intrastate invasives

For the first time ever, aquatic invasive species were found in Wyoming’s largest body of water. Curly pondweed and New Zealand mudsnails were detected and verified in Flaming Gorge Reservoir in southwest Wyoming last summer. Both species were reported to the Wyoming Game and Fish Department from vigilant members of the public — and they are species of AIS that are already present in the state. Nonetheless, the discovery confirms that as much effort the department makes to keep AIS out — they are still spreading within Wyoming’s borders. It’s a call for more diligence from all recreationalists to take care of one of the state’s most prized resources — water.

In 2021 Game and Fish AIS personnel inspected more than 68,000 watercraft at check stations throughout Wyoming, which included 924 decontaminations. The goal of the inspection program is to keep AIS out of the state and to limit the spread within its boundaries, with a larger focus on preventing destructive zebra and quagga mussels from sneaking on a boat. Mussels  have not been found in any natural water in Wyoming to date. However, the discovery of curly pondweed and New Zealand mudsnails in Flaming Gorge is the latest example that AIS can and is being transported within state boundaries. This isn’t a new concern for Game and Fish, but it hammers home the issue since these were found in Wyoming’s largest reservoir, which features a diverse fishery and is popular among boaters and outdoor enthusiasts.

“The discovery of these AIS in the Flaming Gorge Reservoir highlights the need to re-engage our constituents recreating in multiple waters within the state in a short time period the importance of clean, drain, dry and self-inspecting of their own boats,” said Josh Leonard, Game and Fish statewide AIS coordinator. The impacts of curly pondweed and New Zealand mudsnails in Flaming Gorge are uncertain at this point, although early indications suggest impacts may be minimal. Yet, it reinforces the importance for public awareness and preventative measures to keep zebra and quagga mussels out of Wyoming waters, as their introduction could cost millions of dollars in damage to the environment and municipalities. “What is worrisome is if AIS like curly pondweed and New Zealand mudsnails are moving within the state then boat owners, anglers, waterfowl hunters — anybody that’s using water — still aren’t taking all the precautions we need them to take to stop the movement of these species,” said Robb Keith, Game and Fish regional fish supervisor in the Green River Region. “Ultimately, the introduction of quagga and zebra mussels is our greatest concern at the moment.”


Curly culprit

Flaming Gorge is the eighth-known lake or reservoir in Wyoming to have curly pondweed. Eric Hansen, Game and Fish AIS specialist in Green River, said it was found south of the Anvil Draw boat launch. Hansen did extensive monitoring, both on foot and by boat, and also discovered it near the Buckboard Marina area and up by the confluence with the Green and Black’s Fork rivers. “I didn’t find anything in large populations,” he said. “Most were floating, wind drift-type situations.” Hansen said that there have been historical reports of curly pondweed found on the Wyoming side of Flaming Gorge, but it’s presence has not been detected and verified until now.

Curly pondweed is native to Eurasia, Africa and Australia. It was introduced in the United States in the mid-1800s, and is found in almost every state in the continental U.S. It competes with native plants, reduces plant diversity and forms dense mats that impact water-based recreation. The invasive water weed was previously found in Lake Desmet near Buffalo in 2011, in the North Platte River between Seminoe and Pathfinder reservoirs in 2012, Boysen and Keyhole reservoirs in 2013 and in the Shoshone River near Cody in 2014. Hansen said low water and high temperatures at Flaming Gorge could have given curly pondweed the boost it needed to grow last year.

To try and remove curly pondweed at Keyhole Reservoir, Game and Fish has used rakes to manually remove the vegetation. Sometimes the invasive plant will grow so thick there have been instances where kayakers find themselves stuck in sections of the reservoir. Leonard said it is “close to impossible” to eradicate curly pondweed once it has established itself in a large reservoir system. It is more realistic to try and contain it to certain areas or reduce it from high-traffic areas like boat ramps to limit the spread to other waters. Additionally, it is against Game and Fish regulations to transport vegetation on a watercraft at any time. That regulation was made to help reduce the spread of vegetatvie AIS to and within the state. Chemical treatment is an option, but not one Game and Fish is planning to pursue in the near future. Grass carp is a potential biological tool to control curly pondweed because it is a food source. However, grass carp also feed on other aquatic plants and can destroy habitat. Mark Smith, Game and Fish assistant fisheries management coordinator, said Game and Fish has experimented with grass carp as a potential management tool for curly pondweed, but results to this point haven’t been promising.


Sneaky, small snail

New Zealand mudsnails originated from the island country of New Zealand, but are not new to Wyoming. There are populations in five rivers and creeks in Yellowstone National Park, the Snake River and Polecat Creek in Grand Teton National Park, Bass Lake in Fremont County and in the Bighorn, North Platte, Salt, Shoshone and Snake rivers throughout the state. The snails have been present in the lower Green River drainage (below Flaming Gorge Dam) for a while. Hansen said he found them in the Blacks Fork River arm of the reservoir, but none upstream of the reservoir in either river.  “In 2021 it was full bore, and we saw thousands upon thousands of them,” Hansen said. New Zealand mudsnails are 4 to 5 millimeters long and can be spread by fish and birds, natural downstream dispersal and upstream through rheotactic behavior. However, most frequently, it is people and pets that move these tiny creatures inadvertently. 

“Anglers going in and out of waters infested with New Zealand mudsnails can transport them on their waders or shoes and move them around unless they clean off their gear,” Leonard said. “That’s one theory on how they likely got to the U.S. from New Zealand.” The snails also can be transported from one place to another via drift boats and vehicle tires. New Zealand mudsnails can reproduce asexually, therefore only one individual is needed to start a new population. They displace native communities of snails and aquatic invertebrates, and can be a food source for fish, but not a good one for the trout in Flaming Gorge or in other Wyoming waters. “Most trout don’t have robust enough gill rakers to break down the snails within their digestive systems,” Leonard said. “The snails can live through a trout’s digestive tract. It is a negative gain for fish as they spend energy to eat and get no value out of it. That is concerning from a fish health and growth standpoint.”


What’s next

Game and Fish released rapid response plans for 23 Wyoming waters to identify steps that will be taken to contain quagga and zebra mussels if they are detected.  But what about AIS already found in Wyoming and preventing the spread to more waters? Wyoming residents, unless they are leaving the state or recreate at a reservoir with a roving inspector, don’t often have interaction with Game and Fish AIS inspectors, due to the nature of focusing inspection stations at the state borders. “What it highlights is our AIS inspection program is well structured at keeping AIS from coming into our state, but we are not well suited for keeping AIS that are already established in Wyoming from moving around to other water bodies within the state,” Leonard said. “We need to get the word out to all water users who will ultimately be impacted if mussels are established in Wyoming. We can’t be at every water body within our state all the time, so we educate the public and rely heavily on our constituents to understand the issue so they can help be the best stewards of their resources as possible.”

One advantage at Flaming Gorge is there are AIS check stations at the reservoir so inspectors can inform watercraft users about curly pondweed and New Zealand mudsnails as they come and go from the reservoir. It also gives Game and Fish another opportunity to educate people about all AIS. “Education and outreach is the No. 1 pillar of the AIS program,” Hansen said. “There’s no way we can keep everything out with our eyes. Having the public aware and educated on what to look for further helps our cause. It’s never a good thing to have a new species of AIS detected in a new water in the state, but it does bring a lot of attention to the people that love the Flaming Gorge — and there are a lot of them!”

— Robert Gagliardi is the associate editor of Wyoming Wildlife.

For more information about aquatic invasive species in Wyoming go to:

Photographer Info
(WGFD photo)

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