Assessing Our Risks to Prioritize Our Activities

 

The resources to completely defend Lake Vermilion’s fishery and business community will never be available. We’re committed to deploying the resources we can muster on our highest priority risks as efficiently as we can.

Hybrid watermilfoil has moved up the list to our top spot. Little is known about crosses between invasive Eurasian watermilfoil and our native northern watermilfoil, but anecdotal reports suggest some genotypes have increased invasiveness and evidence of herbicide resistance. Ray Newman (MAISRC), in an ongoing study of the distribution of watermilfoil in Minnesota, has found 27 hybrid genotypes in 19 lakes. Some of those lakes had hybrid but neither parent, suggesting hybrid watermilfoil can be moved between lakes with suitable habitat.

In Lake Vermilion, native northern watermilfoil co-exists with other native vegetation. We have no known Eurasian watermilfoil – an indication our habitat may not be suitable. However, at this point, no one knows whether a specific hybrid genotype may find our water chemistry to its liking and overwhelm our native vegetation in specific bays.

Starry stonewort – a relative newcomer to Minnesota’s AIS roster – has been found in 13 lakes, including top-ten walleye lakes Upper Red, Cass and Winnibigoshish, five years after its discovery in Lake Koronis. This grass-like macro algae can produce dense mats, can interfere with recreation, and can alter habitat for young fish. It’s understandable that property values would decrease at lakes and along shorelines with starry.

Early research suggests our water chemistry may be generally low risk for starry. However, we’re early in the game and certain shallow, soft bottom bays may be suitable.

Zebra mussels, on the other hand, have been extensively studied. Zebras need sufficient dissolved calcium – about 20 milligrams per liter – to grow and reproduce. Most of Lake Vermilion is below 13 mg/l – well in the safe zone. An exception is East Two River, which flows into Vermilion’s east basin, with calcium above 20 mg/l at certain times of the year. However, its <7.0 pH prevents zebra mussels from becoming established. To be safe, we will continue to monitor east-basin water chemistry for a few years.

Our current risk assessment – including what we don’t know – is summarized below:

 

Species Introduction Risk Habitat Suitability Impact if Population Established
Fishery & Ecosystem Recreational Boating
Hybrid and Eurasian watermilfoil Eurasian high. Hybrid increasing as more lakes become infested. Generally low. May be suitable in specific bays. Serious stressor. Unknown impact on
each fishery.
Severe in bays with suitable habitat.
Starry stonewort Increasing as more Minnesota lakes become infested. Generally low. May be suitable in specific bays. Serious stressor. Unknown impact on
each fishery.
Severe in bays with suitable habitat.
Zebra mussels Very high. Low. Limited to calcium hotspots with suitable pH? Serious stressor. Filters zooplankton, limiting growth of fry. Negative but water clarity appeals to some.
Spiny waterfleas Found in Big Bay
in 2015.
High in
deep basins.
Serious stressor. Consume zooplankton, limiting growth of fry. Low. Gets tangled in
fishing or recreational gear
Curly-leaf pondweed Present in
4 small areas.
Moderate/high in specific bays. Stress on native plant diversity. Unknown impact on each fishery. May become severe in bays with suitable habitat.
Rusty crayfish Present in east basin and west to Niles Bay. High for sandy, rocky, rubble bottoms. Weed bed destruction impacting several
fish species.
Low to moderate.

 

In addition to the priority threats in the table above, we continually monitor other potential AIS threats with the assistance of RMB Environmental Labs. Examples include Brazilian waterweed, water soldier, brittle naiad, hydrilla, and water hyacinth.