Genetics and Juvenile Abundance Dynamics Show Congruent Patterns of Population Structure for Depleted River Herring Populations in the Upper Chesapeake Bay

River herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) populations have declined dramatically along the U.S. Atlantic coast. Conservation efforts are currently inhibited by an incomplete understanding of stock structure for the upper Chesapeake Bay, which once supported some of the largest spawning runs across the species’ ranges. We collected genetic samples from 512 adult river herring from five rivers and used microsatellites to explore genetic differentiation and population structure. Juvenile abundance indices were also evaluated for spatiotemporal patterns using time series analyses. Statistically significant allelic heterogeneity was observed among most collections, and we identified genetically distinguishable groups for each species. Regression analysis indicated stable or declining juvenile abundance, and empirical orthogonal function analysis supported groupings of tributaries based on temporal patterns in abundance. Results suggest a divide between eastern shore and western shore tributaries, with the Susquehanna River and the head of the bay showing similarities to both groups and possible temporal shifts in genetic structure due to straying. The Patuxent River likely represents a third genetic group for Blueback Herring. Cumulatively, our results suggest at least two genetically distinguishable groups of spawning populations for Alewives and at least three for Blueback Herring; these groups should be considered separately for conservation and management.

Received December 22, 2016; accepted June 3, 2017 Published online August 31, 2017