Recent Changes in the Inshore Forage Fish of Lake Michigan

Abstract

Concerns have been expressed that increasing predatory pressure by salmonids may change the forage fish community of Lake Michigan. A decline in alewife (Alosa pseudoharengus), the major forage fish, would be a forewarning of such a change. Our 1973–82 surveys showed that alewife declined 86% in 1980–82; concurrently, rainbow smelt (Osmerus mordax) and yellow perch (Perca flavescens) increased threefold and fivefold, respectively. Spottail shiner (Notropis hudsonius) and trout-perch (Percopsis omiscomaycus) showed no long-term changes. Bloater (Coregonus hoyi) increased 24-fold since commercial fishing was prohibited in 1976. These trends imply that (1) alewife declined from predatory pressure, (2) alewife suppressed rainbow smelt and yellow perch, presumably by preying on their pelagic larvae, (3) alewife did not substantially affect spottail shiner and trout-perch, presumably because their demersal larvae escaped alewife predation, and (4) overfishing, more than the alewife, suppressed bloater.