Sara Prendergast's Thesis Presentation

Event Date: 
Thursday, August 8, 2019, 3:00 pm

Concept Development Room
4840 S. State Road
Ann Arbor, MI

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



Dr. Karen Alofs, Chair

Dr. Mark Rowe

Dr. Ed Rutherford



 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 state 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 were hatched only at locations along the eastern shoreline. We paired trajectory paths with environmental conditions predicted from a biophysical model. There was a significant relationship between larval daily growth rate and temperature, phytoplankton, detritus, and zooplankton concentrations, and the interaction with larval age. As phytoplankton concentrations decreased, larval growth rates increased. The other variables were positively related to larval growth. Negative larval growth rates were realized under two observed conditions: temperatures below 12.5 °C and phytoplankton concentrations above 154.25 µg L-1, when all other variables were held at their mean. These results suggest areas and environmental conditions that are favorable to young alewife growth in Lake Michigan.