What the tide rolled in…

5 Aug

After a beautiful day of camping and cherry-picking on the scenic Door County peninsula, we strolled down to the Nicolet Bay beach to bask in a colorful sunset – and got a big, slimy surprise.   As little Lake Michigan waves lapped at the shore they littered the sand with tiny shiny bodies.  More silvery slivers bobbed in the water.  The afternoon’s sandcastle moats filled with the bodies of stinky, fishy intruders.  There was a fish kill of alewives (members of the herring family), and thousands of them were washing up on the beach.  Not just our beach!  We found out later, from a walk around and news report, that large parts of Lake Michigan was being coated in a crusty ring-around-the-shoreline of decaying minnows.

Dead alewives wash into a forgotten sandcastle.

Alewives are a non-native fish that hold a bitter-sweet position in the Great Lakes food chain.  Salmon love them – good for the big sport fish.  But alewives are bad news for native lake trout!  They eat the young lake trout when they’re small.  And then, to add insult to injury, when trout grow up and eat the alewives, chemicals in the alewives skin can cause vitamin deficiencies and disrupt trout reproduction.

An article in the Appleton Post Crescent says all the dead fish “might be a sign of a healthy lake”.  I was motivated to look a little deeper into the ecology of the die-off when one of my fellow-campers wondered how on earth tons of dead fish meant a healthy lake.  After a bit of digging I think they may have oversold the healthy lake issue in an attempt to offer reassurance to beach-goers.

Alewives wash ashore with the Lake Michigan waves.

Sure, alewife die-offs are nothing new and, apparently, nothing to cause alarm.  Check out this article in Time Magazine about an alewife die-off in the 1960’s – just imagine bulldozer-loads of tiny dead fish stinking up a sunny beach!  There are various theories about the causes of alewife kills – from minor temperature fluctuations, to localized oxygen depletion when populations boom, or changes in harmful algae populations.  Apparently alewives are a bit delicate in their non-native environment.

It seems perfectly true, an alewife die-off would be a sign of a thriving alewife population.  But, given the trade-off between salmon health and lake trout harm, I’m not convinced that a booming alewife population is the best thing for the overall ecology of the Great Lakes.

In any case, I’m darned glad we got some good swimming time in earlier in the afternoon before the tide-o-death rolled in.


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