EVIDENCE FOR ALEWIFE (ALOSA-PSEUDOHARENGUS) PREDATION ON THE EUROPEAN CLADOCERAN BYTHOTREPHES-CEDERSTROEMI IN NORTHERN LAKE-MICHIGAN

Stomach contents of 10 alewife (Alosa pseudoharengus), 3 bloaters (Coregonus hoyi), 1 rainbow smelt (Osmerus mordax), 4 chinook salmon (Oncorhynchus tshawytscha), and 1 lake trout (Salvelinus namaycush) were examined for the presence of the European cladoceran, Bythotrephes cederstroemi. Fish were collected commercially (by gillnetters and sport charters) in July and August of 1988 in the North Manitou Island area of Lake Michigan when B. cederstroemi were abundant. The zooplankter was found in all alewife examined and its remains normally filled the entire stomach cavity. The only other evidence for fish predation on B. cederstroemi was found in the stomach from a 0.5 kg chinook salmon. A few caudal spine fragments were found in the stomach of one bloater yet because the stomach was full of the bent hie amphipod, Pontoporeia hoyi, it was hypothesized that the fish acquired the remains from the sediments. Stomachs of other fish were either empty or did not contain B. cederstroemi. Although limited, these data are the first conclusive evidence that the economically important alewife prey upon the exotic B. cederstroemi in the open waters of the Great Lakes. © 1990, International Association for Great Lakes Research. All rights reserved.