Remember, alewife are naturally a sea run fish. They are much like striped bass or American shad(who are closely related to them). They live most of their lives out at sea where they feed on small shrimp, fish larvae(of saltwater species which over many centuries of evolution have evolved to this predation) and once they mature, they make spring spawning runs into freshwater rivers where they spawn. The YOY stay in the estuary of the river and then migrate out to the ocean the next year to start the cycle all over again... In a lake environment, fish found in these lakes have not evolved to this type of predation and alewife are not completely evolved to lake life. Often having mass winter die offs not found in sea run populations. I have fished lakes with alewife which have great fishing for game fish. Raystown Lake in Pennsylvania rings a bell. It is loaded with alewife but has a healthy population of walleye, lake trout, stripers, SMB, LMB and others... However, other than the LMB and SMB, the others are almost entirely maintained by annual stockings of advanced fingerlings.
