FRESHWATER INFLUENCES ON STRIPED BASS POPULATION DYNAMICS 



J. A. Mihursky, W. R. Boynton, E. M. Setzler-Hamilton, and K. V. Wood 



University of Maryland, Center for Environmental and Estuarine Studies 

 Chesapeake Biological Laboratory, Solomons, Maryland 



and 



T. T. Pol gar 



University of Maryland, Center for Environmental and Estuarine Studies 

 Chesapeake Biological Laboratory, Solomons, Maryland, and 

 Martin Marietta Corporation, Environmental Center 

 Baltimore, Maryland 



ABSTRACT 



A population dynamics study of 

 striped bass ( Mo rone saxatilis) was 

 conducted in the Potomac Estuary from 

 1974-1977. Investigations included 

 measurements of hydrodynamic char- 

 acteristics; water quality, phyto- 

 plankton; zooplankton; and striped 

 bass egg, larval, juvenile, and adult 

 stages. Larval and juvenile food 

 habit data were also developed. 

 Biological data indicated that 

 striped bass year-class success, as 

 measured by juvenile abundance, was 

 not closely correlated to abundance 

 of spawning stock, number of eggs 

 deposited or early, non-feeding 

 Larva] stages. These results sug- 

 gested that densi ty- independent as 

 opposed to density-dependent mech- 

 anisms controlled the erratic pat- 

 terns of year-class success of this 

 species. Climatic data were compared 

 to available juvenile abundance data 

 for a 25-year period. Strong year- 

 classes were correlated with colder 

 than average winters (December) which 

 were followed by above average spring 

 (April) freshwater runoft to the 

 estuary. Larval food habit studies, 

 coupled with earlier work concerning 



larval transport suggested that high 

 densities of zooplankton at the time 

 of first larval feeding and the spa- 

 tial distribution of the spawning 

 stock contributed to larval survivor- 

 ship and consequent establishment of 

 year-class strength. In order to 

 provide projected freshwater supplies 

 for human activity in the Washington, 

 D.C., metropolitan region a number 

 of engineering devices have been 

 proposed, including upstream reser- 

 voirs, inter-connections to existing 

 reservoirs, deep-well additions and 

 advanced waste water treatment and 

 reutilization. A number of the 

 above devices have the potential to 

 change hydraulic regimes in the 

 Potomac. The effects of these 

 changes are discussed and evaluated 

 with regard to maintenance of the 

 striped bass stock. 



'•'•"Contrib. 1024, Center for Environ- 

 ment and Estuarine Studies of the 

 University of Maryland. 



INTRODUCTION 



The striped bass is an important 

 commercial and recreational fish 

 native to the East Coast of the 

 United States. It is an anadromous 

 species that migrates during the 

 spawning season from coastal high 

 salinity areas to the fresh or 



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