Salmon are the symptom
Lake Michigan salmon fans are all abuzz with the recent announcement that beginning next spring 68 percent fewer king salmon will be stocked in Lake Michigan. Why? Because the best science says there are so many salmon in the lake they are going to eat all the alewives. (Alewives are the small baitfish king salmon depend on for food.)
There are many reasons for this impending disaster and plenty of fingers pointing in many directions. Some opine the Lake Michigan states have long been over-stocking the lake. Many point their finger to Michigan’s upper Lake Michigan tributaries, which have proven to be great places for king salmon to reproduce.Some pin the blame on wild-spawned Lake Huron kings, which now migrate under the Mackinaw Bridge to forage in Lake Michigan, having eaten all the alewives in their lake.
An over-abundance of salmon, however, is only the symptom of the problem. The actual blame should go to zebra and quagga mussels. These closely related invaders from eastern Europe were first found in the Great Lakes in 1988 and quickly spread throughout the system. Since they are mussels, they live on the bottom of the lakes and have sucked the life out of the bottom of the food chain.
Places where there once was only soil or rocks on the bottom of the lake are now coated with mussels. And that’s nearly everywhere in Lake Michigan. Every bit of algae consumed by a zebra mussel and every tiny zooplankton sucked in by a quagga is one less bit of food for tiny native fish and alewives. Sure, salmon eat a lot of alewives, but the mussels' control over the bottom of the food chain is the reason so few alewives are available for the salmon to eat.