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

ACKNOWLEDGMENTS

We thank R. Aguilar, M. Goodison, A. Hines, M. Kramer, K. Richie, and P. Roberts (Smithsonian Environmental Research Center [SERC]) for assisting with sample collection in the Choptank and Nanticoke rivers; R. Aguilar for helpful feedback on early drafts of the manuscript; B. Richardson and C. Stence (MD-DNR) for supplying fin clips from the Susquehanna and Patuxent rivers; E. Durell for providing juvenile abundance data; and C. Schlick and K. de Mutsert (George Mason University) for providing fin clips for the Potomac River. S. Blinebry and R. Thomas provided technical support with genotyping at the Marine Conservation Molecular Facility, Duke University Marine Laboratory. Two reviewers supplied comments that improved the manuscript. Funding for this work was provided by National Fish and Wildlife Foundation awards to M.B.O. (Award Numbers 0104.12.034809, 0104.13.040321, and 0104.14.045567) and E.P.P. (Award Numbers 0104.14.041425 and 0104.10.036436), the Atlantic States Marine Fisheries Commission (Award Numbers 15-0105 and 15-0102), and the Smithsonian Institution Office of the Under Secretary for Science. E.P.P. was partially supported by funding from the National Oceanic and Atmospheric Administration’s Cooperative Institute for Marine Ecosystems and Climate. M.B.O. was partially supported by a SERC Postdoctoral Fellowship.