by the Chaffee Amendment provides for 

 an emergency 3-year study of striped 

 bass populations. This new amend- 

 ment recognized that "this species 

 is experiencing a grave crises" and 

 calls for two major efforts: (1) to 

 monitor the status of existing popu- 

 lations, and (2) to identify factors 

 responsible for the decline in 

 stocks. The major emphasis of the 

 former deals with describing egg, 

 larval, and juvenile stocks, while 

 the latter deals with toxicological 

 investigations . 



While contaminants may be im- 

 portant factors in some areas, we 

 hypothesize that in the Potomac 

 Estuary extrinsic climate factors in 

 combination with spawning behavior 

 largely determine year-class 

 strength. Our purpose here is to 

 present data in support of this hypo- 

 thesis and to speculate on possible 

 impacts on striped bass stocks re- 

 lated to changes in the volume and 

 timing of freshwater discharges. 



As part of the power industry's 

 response to projected electricity 

 demands, a nuclear steam electric 

 station was proposed at Douglas Point 

 on the Potomac Estuary, a location 

 that has been identified as part of 

 the Potomac striped bass spawning 

 grounds (Figure 1). The Maryland 

 Department of Natural Resources, 

 initiated a target species approach 

 to examining the possible damage 

 factor to the striped bass fisheries 

 of the Potomac. The major issue con- 

 cerned the effect of increased mor- 

 tality rates of egg and larval stages 

 caused by pumped-entrainment activity 

 of the proposed power plant cooling 

 water system on future fishable 

 stocks. Thus a population dynamics 

 study was conducted between 1974 and 

 1977 and included investigations of 

 river hydrology, water quality, 

 phytoplankton and zooplankton distri- 

 butions, and quantitative character- 

 ization of the temporal and spatial 

 abundance of egg, larval, juvenile 

 and adult stages of striped bass. 



POTOMAC ESTUARY STUDY 



The Potomac Estuary (Figure 1), 

 a subsystem of the Chesapeake Bay, 

 was declared a national estuary by 

 President Johnson. The estuary has 

 been utilized for transportation, 

 recreation, fisheries exploitation 

 and sewage disposal since colonial 

 times. Industrial activity is rel- 

 atively low compared to most East 

 Coast estuaries. Population growth 

 in the Washington, D.C. metropolitan 

 area, located in the upper tidal 

 Potomac, has been substantial in the 

 last few decades. This growth has 

 caused increased demands for 

 electricity, domestic water supplies 

 and has resulted in the release of 

 increasing amounts of treated-sewage 

 effluent to the upper Potomac 

 Estuary. 



Summarized in Figure 2 are striped 

 bass egg and larval densities typical 

 of all years of our study. Several 

 key points can be made from these 

 time-space depictions. While egg 

 deposition occurred throughout most 

 of the study area, highest egg densi- 

 ties appeared progressively upriver 

 from those areas where spawning was 

 initiated. This pattern was sup- 

 ported by data from adult stock 

 assessment studies (Jones et al. 

 1978). Secondly, despite an average 

 net downstream transport of several 

 centimeters per second, peak densi- 

 ties of all larval stages persisted 

 through time in the same area of the 

 estuary or showed a slight upstream 

 movement. It appears that the stable 

 position of peak larval densities was 

 the result of the successful recruit- 

 ment of eggs deposited late in the 

 spawning season at upriver loca- 

 tions. Lastly, there was an abrupt 



151 



