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    Saint Croix

    National Scenic Riverway WI,MN

A Surprising Discovery

June 29, 2012 Posted by: Park Ranger Linda Krings

If you move at a rivers pace, the St. Croix can share many stories and reveal surprising mysteries in its brown-tinted waters. 

Several days ago one of these appeared as I stopped on an island south of The Dalles. As I exit my kayak I have a habit of immediately scanning the ground for tracks….signs of who or what had been there before me.  

Almost immediately I spotted a small freshwater mussel in the shallow water, and as I tried to identify the species I realized I was looking at a young heelsplitter. (This species gets its name due to having a very long, narrow, and almost pointed edge on one side.) In eleven years of working on the St. Croix I have seen a number of living heelsplitter's, but never a young one. This was amazing! As I scanned the sandy area I spotted a second, and then the empty shell of a third.

Each native freshwater mussel species has a preference for the habitat in which it lives. While one species may prefer an area with calm water and a gravelly bottom, a different type might only be found in areas of moving water with a muddy substrate. Typically they do not choose live in deep sandy water.

Why were these in this area?

My best guess is that recent floods displaced them from their normal habitat. I know the mussels of the Saint Croix face many challenges, yet they take care of the river by filtering impurities out of the water which is just one of the reasons I have grown fond of them. It may sound strange, but finding these two juvenile heelsplitters was an amazing and unexpected experience which I will treasure.

The difficult part of that day was realizing that these heelsplitters may not survive where they landed. The mussels of the St. Croix are protected and are not to be disturbed by humans. Park staff may rmove mussels as part of approved research, or move them a short distance on rare occasions when they become stranded above water due to severe drought; it is not OK to remove them or move them to a completely new location. Even the shells of dead mussels are protected within the Riverway.

I feel fortunate to have seen these young heelsplitters, and I when I pass this island in the future I will continue to ponder this amazing species of wildlife.


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Did You Know?

What looks like a striped fish with several tails is actually the opening of the mussel shell which is hard to see.

Mussels rely on fish to carry their young around until they are old enough to drop to the river bottom. To attract the fish and attach their young, mussels put on displays that make fish think they are fish or other food. The mussel shell, which is all we normally see, is now barely visible.