Energy Content of Young Alewives in Eastern Lake Michigan and Muskegon Lake, a Connected Drowned River Mouth Lake

Abstract

Energy content is an important determinant of an individual fish’s condition and a key input variable for bioenergetics applications. Energy content of young fish can change rapidly during ontogeny; given the numerical abundance and high mass‐specific metabolic rates of young fish, it is particularly important to obtain detailed information on their energy content. To this end, we quantified the total body energy content and energy density of economically and ecologically important young (age‐0–1) nonnative alewives Alosa pseudoharengus collected during 1998–2003 in eastern Lake Michigan and Muskegon Lake, a connected drowned river mouth lake. Our analysis demonstrates that energy content of young alewives varies across years, seasons, lakes, and ontogeny. Consistent with previous observations of size‐dependent overwinter mortality, young alewives deplete a large amount of body energy between late fall and late spring (i.e., declines in length‐specific energy content and energy density occur overwinter). Interestingly, unlike several past studies of young fish in their native range, size‐specific energy content of young alewives does not appear to increase over the summer and fall (there is no evidence of increased energy storage in preparation for the resource‐scarce winter period). Finally, our measured values are similar to the few previously published energy density values for age‐0 alewives. The high degree of variation in the energy content of young fish emphasizes the necessity of using appropriate energy measures for bioenergetics applications to inform fisheries management.