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

Abstract

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

Environmental DNA reveals anadromous river herring habitat use and recolonization after restoration of aquatic connectivity

“…The apparent positive association between agriculture and detection probability could be driven by the fact that Alewife eDNA detections, which were more common overall (98 Alewife to 62 Blueback Herring), were much more likely on the eastern shore (Plough et al, 2018), which is more agricultural than the western shore. However, when restricting the analysis to the eastern shore dataset, the percent of cropland was no longer in the top three most important variables (Table 4) making it difficult to determine whether the observed effect in the full dataset is driven by differences in land use between shores, by genetic stock structure (Ogburn et al, 2017), or other factors. Habitats proximal to agricultural land may harbor more river herring because of increased productivity driven by high nutrient inputs (Jordan et al, 1997).…”

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“…from pre-industrial times) supported more river herring due to any number of physical, biological, or habitat features of the particular rivers that we sampled, which may be completely unrelated to recent human activities. Genetic differences between eastern and western shore stocks of both alewife and blueback herring have also been observed using microsatellite markers [ 87 ], adding additional uncertainty in the potential causes of patterns in abundance.…”

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