Some impressive looking numbers
BY Dick Osgood– Guest Columnist
Maybe it is just me, but I am impressed by numbers. I have been piping off about the ills of zebra mussels for a long time now, about how quickly they expand and how bad they will be for the lake. However, I find numbers provide perspective.
Lake Mille Lacs has had zebra mussels longer than Lake Minnetonka, so it provides some guideposts for us to consider.
This year, 2012, represents the third year since zebra mussels were discovered in Lake Minnetonka. This year, we have all begun to actually see zebra mussels – littered along the lakeshore, clinging to weeds and attached to underwater structures.
In Lake Mille Lacs, zebra mussels were measured at densities of only one per 420 square-feet in 2007, the third year following their discovery. However, by 2012, the eighth year following their discovery, zebra mussels averaged 1,300 per square-foot – more than a 500,000-fold increase in five years! And they are still increasing.
At this density, zebra mussels are filtering the entire volume of Lake Mille Lacs several times each year. The “stuff” filtered by zebra mussels include algae and other single-celled organisms that form the base of the food chain. The Minnesota Department of Natural Resources reports that perch numbers are down as well as other “feed” fish. And walleye numbers are the lowest in 40 years. Coincidence? I don’t think so.
What will Lake Minnetonka look like five years from now? Of course Mille Lacs and Minnetonka are two different lakes, but the magnitude of impacts, I expect, will be similar.
Note that zebra mussel densities are reported differently for the two lakes. In Mille Lacs, the densities are actual densities of zebra mussels on the lake bottom and in Minnetonka, the densities are reported (recently by the Minnehaha Creek Watershed District) from test plates, so they cannot be directly compared.
So, we have not yet seen how bad zebra mussels will be in Lake Minnetonka. I hope that we do not become complacent and think that now that we have had zebra mussels for three years, this ain’t so bad?
This ought to motive us to redouble our resolve to keep new AIS out.
I was also disappointed (although not surprised) that the DNR reported finding zebra mussels in Rose and Irene Lakes (near Alexandria) following an early detection and aggressive rapid response in 2011.
At the international meeting of the North American Lake Management Society earlier this month, I chatted with numerous colleagues about this and the consensus was that AIS are notoriously difficult to detect early and in most cases, practically impossible to eradicate. According to an internationally noted aquatic plant ecologist, unless we are prepared for the ‘nuclear option’ (heavy chemical treatments), we cannot eradicate new invasive plant infestations.
This should provide another motivation to redouble our resolve.
These zebra mussel numbers impress me, albeit not in a good way. There are more impressive numbers: The number of additional aquatic invasive species heading our way (about two dozen) or the cost of controlling the AIS now in our watershed (at least $1 million per year – Lake Minnetonka accounts for 84 percent of that). Or how about this one, the surcharge for a boat owner to help pay for AIS management in Minnesota — $1.67 per year.
Dick Osgood is Executive Director of the Lake Minnetonka Association. The Lake Minnetonka Association is the voice for Lake Minnetonka lakeshore owners and businesses. Dick is a Certified Lake Manager and Past-President of the North American Lake Management Society. See LMAssociation.org.