Life History Traits and Population Dynamics of River Herring, Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis in Potomac River Tributaries




Schlick, Catherine Jean Carroll

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Anadromous river herring, Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis, were valuable fisheries that declined to such an extent that moratoria were established throughout much of their range, including all of the Chesapeake Bay. The presumptive causes of decline are overfishing and habitat degradation. The goals of this research were to examine the life history traits of river herring in Potomac River tributaries and determine if the tributaries serve as successful spawning and nursery habitats after years of habitat alterations. A stage-based model of populations in Potomac River tributaries was developed with site-specific growth rates, mortality rates, and maturity schedules. Adults were collected in Pohick Creek, Accotink Creek, and Cameron Run, juveniles in Gunston Cove and Hunting Creek, and larvae in all locations. Otoliths were extracted to estimate age (adults in years and young-of-year (YOY) in days) and scales were collected from adults to estimate spawning age. Of the eight growth models tested, the best-fit model was the logistic for adults and the von Bertalanffy for YOY; however best- and worst-fit models were <2% different. Adult females grew faster, larger, and matured earlier than males for both species. Growth differed between years for both species of YOY, and between monthly cohorts for Blueback Herring YOY. Mortality was more variable for Alewife than for Blueback Herring. The model was a good fit for YOY Alewife but not for Blueback Herring. The model predicted that year class strength was variable for both species, with surviving juveniles replacing 13.8%, 130.4%, and 6.5% of spawning Alewife, and 1.8%, 0.5%, and 0.4% of adult Blueback Herring each year from 2013 to 2015. However, the models were sensitive to the juvenile mortality rate and both populations were increasing when lower juvenile mortality rates, similar to other Virginia rivers, were utilized. This dissertation provides needed life history characteristics for all stages of development for river herring found in Potomac River tributaries.



Environmental science, Ecology, Chesapeake Bay, Growth rates, Mortality rates, Nursery habitat, River herring, Von Bertalanffy