Early life history of Lake Michigan alewives (Alosa pseudoharengus) inferred from intra-otolith stable isotope ratios

We apply a robotic micromilling technique to the sampling of young-of-the-year (YOY) and 1+ otoliths from alewives (Alosa pseudoharengus) captured in different habitat types of Lake Michigan during 2001–2003. δ18O values of otolith cores of YOY alewives from Muskegon Lake (a sheltered, drowned river mouth lake connected to Lake Michigan), Muskegon Channel (which connects Muskegon Lake to Lake Michigan), and Lake Michigan proper are compared with δ18O values of ambient water from different potential early life habitats. Otolith core δ18O values used in conjunction with δ13C values serve as good discriminators of nursery areas. The majority of YOY alewives captured in Muskegon Lake emerge and grow in this habitat, whereas the majority of YOY alewives captured in Lake Michigan emerge and grow in Lake Michigan. In addition, early-life movements of alewives between the two lakes are documented but limited. Even if drowned river mouth lakes are more favorable for alewife growth and survival, their contribution to the Lake Michigan population could be limited because all of the 1+ alewives were individuals that spent their early life in Lake Michigan. The application of high-resolution isotope analysis of small otoliths of forage fish for fish population dynamics studies appears promising.