Evaluating the potential for pre-zygotic isolation and hybridization between landlocked and anadromous alewife (Alosa pseudoharengus) following secondary contact

The recent increase of river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of pre-zygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith derived age estimates. In addition, we analyzed long-term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3% to 13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The ...