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The range-wide stock and population genetic structure of alewife and blueback herring is currently unknown, but recent research using newly developed Single Nucleotide Polymorphisms (SNPs) for specimens collected across their entire geographic range should provide this vital information. Prior research to inform the spatial scale of stock structure has used genetic markers (i.e., microsatellites), life history information, and morphometric data. To date, genetic data suggests evidence of regional stock complexes for both alewife and blueback herring, even though many rivers comprise genetically distinguishable groups.  Migration and mixing patterns of alewives and blueback herring in the ocean are currently unknown, though regional stock mixing is suspected, and efforts are currently underway to better understand river herring marine ecology. Otolith microchemistry may help inform stock structure where molecular markers provide only course resolution, and important efforts have occurred. When considering a rangewide perspective, standardized approaches to stock structure are important for providing comparable datasets.

The river herring Technical Expert Working Group (TEWG) Genetics/Hybrids/Landlocked Subgroup has considered issues related to the above specific to rangewide stock structure. Also, this subgroup has considered possible effects from hybridization, understanding the effects of stocking on genetic diversity, and any impacts landlocked populations may have on anadromous forms via introgression following dam removal and fish passage improvement projects. Additional information on these discussions, including identified research needs to inform the topic and ongoing efforts can be found at: