Abstract

Abstract The exotic cladoceran Bythotrephes longimanus is an important food resource for eastern Lake Erie rainbow smelt Osmerus mordax. Bythotrephes possesses a long, chitinous caudal spine that is generally used to quantify its presence in fish diet studies despite concerns that it may be retained within fish stomachs longer than other prey items. We investigated spine retention in rainbow smelt collected in the eastern basin of Lake Erie in June (day and night), July (night), and October (night) of 1998 and 1999. To assess differential retention of Bythotrephes spines in rainbow smelt stomachs, we compared counts of Bythotrephes caudal spines to direct counts of Bythotrephes bodies or mandible pairs. Retention of caudal spines was evident in yearling and older (age-1+) rainbow smelt caught during the day in June as well as in age-1+ fish caught at night in July and October and in young-of-year fish captured at night in October. Smelt stomach fullness decreased with time after sunset, indicating lower n...

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