According to a rather lengthy report by the Michigan DNA, most of which is over my head.
The decline of Alewives in Lake Huron is the cause.
I've been told that they are moving over to Lake Michigan which has not had a decline of Alewives.
The salmon were introduced to control the Alewife population and the report aludes to their as being a plus for our native fish.
Hopefully one of you can decifer the report and tell the story better.

Jack