First‐Year Growth, Condition, and Size‐Selective Winter Mortality of Freshwater Drum in the Lower Missouri River

Abstract

Abstract We compared first-year growth and relative condition (Kn ) of the 1997 and 1998 year-classes of freshwater drum Aplodinotus grunniens among three sites in a 235-km reach of the channelized Missouri River and tested for the occurrence of size-selective overwinter mortality during the first winter. Prewinter mean length was 15 mm greater, mean weight was 8 g greater, and mean Kn was 5% greater at the upstream site than at the downstream site. The prewinter mean length of age-0 freshwater drum was significantly greater in 1997 (115 mm) than in 1998 (109 mm), but Kn was significantly greater in 1998 (107) than in 1997 (102). There was no evidence that density-dependent interactions influenced prewinter growth and Kn. Size-selective overwinter mortality of the smallest size-classes of freshwater drum occurred at two of three sites during the 1997–1998 winter, and Kn decreased 9–15%. Size-selective overwinter mortality of the 1998 cohort of freshwater drum did not occur during the 1998–1999 winter, and...