Physical and biological influences on daily growth rate of larval alewife (Alosa pseudoharengus) in Lake Michigan

Abstract

Alewife is an invasive fish species in the Great Lakes that serves as prey for top piscivores but also causes reproductive failure of some native species. Environmental conditions generating variability in annual abundance of young alewife are poorly known, but are hypothesized to occur during the sensitive larval stage through advection of larvae into, or away from areas that support rapid larval growth. We modeled transport of alewife larvae from capture to hatch locations, and tested the hypothesis that daily growth of larval alewife can be predicted from environmental conditions. We analyzed growth rates of larval alewife that were sampled from multiple sites in Lake Michigan in July 2015, and estimated their ages and daily growth rates by counting and measuring daily increment widths of their otoliths. We used a Lagrangian particle dispersion model to conduct a backwards trajectory analysis of known-aged larvae from their capture locations to their hatch locations. The trajectory results indicated that larvae collected from sites in western and eastern Lake Michigan hatched at locations along the eastern shoreline. We paired trajectory paths with environmental conditions predicted from a biophysical model. We used a mixed model and found a significant positive relationship between larval daily growth rate and temperature, detritus, and zooplankton concentrations. These results suggest areas and environmental conditions that are favorable to young alewife growth in Lake Michigan.