Zebra mussel spread prompts calls for more aggressive prevention strategies for aquatic invasive species
Since their introduction in the state less than a decade ago, zebra mussels have found their way into 13 bodies of water across South Dakota, most notably leaping westward into Pactola Reservoir last month. Some interest groups think the Department of Game, Fish and Parks could be doing more to slow the spread.
SIOUX FALLS, S.D. — Despite a ramped-up state effort to address the threat of aquatic invasive species, zebra mussel infestations this summer reached new ground in the northeastern and western parts of the state, prompting calls from interest groups for greater investment into prevention.
The presence of the invasive mollusk, which is usually no bigger than a fingernail, was confirmed in the Pactola Reservoir in the Black Hills on July 14 and Enemy Swim Lake in northeastern South Dakota on July 25.
“Game, Fish and Parks works with the resources that they have, we understand that. But we'd also like to see them help advocate for a stronger fight against invasive species, and that's gonna take more resources,” Dan Loveland told Forum News Service in a phone interview on Monday, Aug. 15. Loveland is president of the South Dakota Lake and Streams Association. “Ultimately, a dedicated funding mechanism for fighting invasive species is going to need to be put in place in South Dakota.”
Most states surrounding South Dakota have funding mechanisms specifically dedicated to the prevention of aquatic invasive species, which vary in cost and form but generally involve sticker fees for boat registration or add-ons to fishing licenses.
The discovery of zebra mussels at Pactola Reservoir west of Rapid City, which represents the furthest westward spread of the mollusk in the state, is being closely monitored by Wyoming and Montana, states which have thus far avoided infestation. Sara Dirienzo, the public information officer for the Wyoming Game and Fish Department, said the state closed LAK Reservoir on Aug. 1 “to limit the possibility of zebra mussel spread.”
Zebra mussels are a mollusk native to eastern Europe, making their way onto commercial vessels that traveled from the continent to the Great Lakes in the late 1980s. They have since spread across more than 30 states, mainly through the nation’s major river systems, though they can only spread to more isolated bodies of water by attaching to boaters.
In 2015, the mussels were discovered in South Dakota in Lewis and Clark Lake; since then, they have come to populate at least 13 lakes and river systems in the state. The small mollusk is a “filter feeder” that can alter lake ecosystems “from the bottom up” by consuming key food sources like algae. It can also damage water infrastructure and poses a danger to recreation due to its sharp edges.
A spokesperson for the Game, Fish and Parks department told Forum News Service in an email that “few options exist for extirpating zebra mussels from a waterbody,” and called these options “cost-prohibitive.”
“At present, no plans are in place to attempt to rid any waters in South Dakota of zebra mussels and efforts are focused on slowing the spread through outreach and education of users,” the spokesperson continued.
Boat inspections by GFP have increased rapidly, from 2,048 in 2019 to 14,556 in 2021. According to a report released July 25 examining current mitigation efforts for aquatic invasive species, boat inspections this year have increased by 16.6% compared to last year.
The 12 boat inspection sites across the state draw a major part of their funding from federal sources such as the Bureau of Reclamation and the Fish and Wildlife Service. However, some participants in a forum discussing aquatic invasive species on Aug. 12 near Lake Pickerel noted that relying on that funding has resulted in these sites being heavily concentrated in the western part of the state, due to federal interest in preventing infestation in national parks.
“More boat inspections need to take place, particularly in eastern South Dakota, where the vast majority of lakes are located,” said Loveland, whose organization sponsored the forum. “This is going to require an increase in staffing and refocusing their resources.”
Wyoming maintains around 60 boat inspection sites during the summer season.
Loveland added that, while zebra mussels have received a high amount of media attention, the investment in watercraft inspection is also needed to prevent the spread of other invasive species and plants. One concern mentioned by multiple sources is the Eurasian watermilfoil, an invasive plant in at least four lakes in South Dakota that can grow at a staggering rate and seriously affect recreation.
In a worrying combination for those fighting aquatic invasive species, zebra mussels and their larvae have begun attaching themselves to the stems of Eurasian watermilfoil, which can easily attach to boats, trailers and other vehicles.
“It's much easier to spread weeds than it is just a straight zebra mussel. So it's a whole other venue for spreading,” Kristopher Stahr, the aquatic invasive species program manager in Nebraska, told Forum News Service on Aug. 15 “A region wide approach has to discuss some of these things. I mentioned to some of our folks that we have zebra mussels attached to milfoil, and not many folks had heard of that.”