Local genetic adaptation and homing behavior in anadromous fish favors the formation of local populations across their geographic range of distribution. Spawning- and natal-site fidelity repeated over generations restricts gene flow and allows genetic differences to accumulate resulting in reproductive isolation. This leads to progressive genetic differentiation and population structuring among different river populations.
Alewife, Alosa pseudoharengus, are anadromous fish which are estimated to have high rates of reproductive fidelity and hence might show population structuring among different breeding streams. Alewife are fish of economic importance since they have both commercial and recreational value. Alewife populations have been declining over the past decades and conservation measures to restore the populations have been implemented. Since maintaining genetic integrity of natural populations is one of the main concerns, identification of population structure can assist in designing appropriate restocking programs.
In this study, I used microsatellite markers developed for shad to study population structuring in alewife. Samples were collected from two sites in Connecticut and one in Lake Michigan and genetic differentiation among these populations was estimated using five microsatellite loci. My studies indicate that microsatellite loci developed for shad can be used for alewife. Results from this preliminary study indicated subtle but significant genetic differentiation among populations. This suggests that care should be taken when restocking alewife from different sites in order to maintain genetic diversity among these populations
