Muskrats love fluctuating water levels. Property owners, not so much.

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Muskrats exiting their home. Image: Tom Koerner/USFWS

By Marshall Lee Weimer

Before surveying muskrats along the St. Lawrence River as a master’s student, Alex Kua didn’t know they existed.

The aquatic rodent quickly captured his attention.

Little was known then about the impacts muskrats have on their environment, said Kua, now a researcher at the State University of New York. He wanted to know how muskrats shape their surrounding plant communities.

A greater understanding of their impact could help guide understanding of their dependence on Great Lakes water levels and their related ecosystem roles. Better understanding the connection between water levels and regulation practices could improve conservation projects in the region.

Kua partnered with John Stella and John M. Farrell, professors at the State University of New York’s College of Environmental Science and Forestry, in 2020 to study if muskrats enhance plant diversity on the St. Lawrence River.

“It was a good opportunity to see muskrats as ecosystem engineers,” Kua said.

Ecosystem engineers are animals that significantly modify their habitats and have an outsized influence on other organisms. They are crucial members of their ecosystems, maintaining the health and stability of the environment they reside in. Many animals can be ecosystem engineers, such as beavers and their dam-building.

Kua is the first person to link muskrat housebuilding to increased plant diversity. Muskrats remove invasive cattails and keep their homes drier than the surrounding area. The different conditions allowed a larger diversity of plants to grow in muskrat-occupied wetlands.

In large numbers, muskrats can also create “eat-outs,” Farrell said. They can change vegetation as they consume large swaths of plants, creating space for other wetland species. Eating all those plants combined with housebuilding can promote biodiversity, and more resilient wetlands.

Muskrats do not always engineer their ecosystems, Kua said.

“It is difficult to say muskrats are ecosystem engineers like beavers,” he said. They play their role best as an aid to restoration, encouraging large-scale change through small actions.

Muskrats change their engineering behavior under certain conditions. The most important condition is a high winter water level. Without it, muskrats will burrow in river channels instead of build houses on floodplains.

Under natural conditions, both Lake Ontario and the St. Lawrence River fluctuate. After the construction of the Moses-Saunders Power Dam at the northernmost tip of New York in 1958, the water levels were suppressed by the International Joint Commission, a Canada-US agency that prevents and resolves disputes over shared waters.

But as a result, large stretches of invasive cattails took over the wetlands, damaging the entire ecosystem.

The commission regulates water levels to balance complex interests, such as shipping, hydropower, recreation and biodiversity.

These interests create tradeoffs. And that creates controversies. In the case of the muskrat, biodiversity gains require high water. But high water creates big problems for lakeshore homeowners and communities, including Montreal.

After years researching how to best balance competing interests, the commission found that any deviation from the current plan would damage shoreline property, said Frank Bevacqua, a public information officer with the International Joint Commission.

“The study really polarized the community, no one liked what the report had to say,” he said. None of the plans could produce less flood damage, so the communities didn’t want change.

After years of organized community resistance to proposed plans, the commission created Plan 2014 – to encourage fluctuating water levels while minimizing property damage. The U.S. and Canada approved the plan in late 2016 to begin the following year.

“The timing could not have been worse,” said Jim Howe, chapter director for The Nature Conservancy in central & western New York.

In the spring of 2017, record rainfall caused flooding that damaged property. A similar flood occurred in 2019. Residents and some public officials, including New York Gov. Andrew Cuomo, blamed Plan 2014 for the floods.

No plan could prevent a flood in 2017 and 2019, Bevacqua said. The lake has always flooded, even before Plan 2014.

Low winter water decreases flood risk, but muskrats will not build houses then. That means they cannot engineer their environment and diversify the plant community. Their success in doing that also indicates the success of coastal habitats providing other ecological services.

Bevacqua said eliminating damages is beyond the control of the commission and is more reliably addressed through coastal resilience, the ability of a coastline community to recover naturally from major damage. Muskrats could help improve coastal resilience through their home building by stabilizing wetlands that would absorb flood damage.

Dissatisfaction with Plan 2014 is strong among shoreline residents, Howe said. Although an effective restoration tool, residents are against using fluctuating lake levels for conservation. But that does not mean shoreline residents oppose conservation of wetlands and watersheds in northern New York.

“You can’t keep the lake in a straitjacket,” Howe said.

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