determining the nutritional history of a given group of larvae is not readily 

 obtainable. Even where data are available on the spacial distribution and 

 density of potential food organisms, the frequency with which larvae actually 

 encounter suitable prey can never be known with any degree of accuracy (1 1). 



In assessing the effects of power generating plants on striped bass 

 populations, it is necessary to estimate the rates of natural and plant induced 

 mortality among the pelagic larvae. Life-stage duration estimates, coupled with 

 estimates of stage-specific vulnerability to plant entrainment, may be used to 

 determine the extent of losses that may be attributed to the operation of a 

 particular plant. 



Larval mortality rates in nature are frequently estimated on the basis of the 

 relative frequency of occurrence of larvae of various presumed age -classes in 

 ichthyoplankton collections made throughout the period of larval abundance 

 in the water column. The results of this study suggest that the occurrence of 

 large numbers of early post yolk sac larvae in such collections may be a 

 reflection of a period of suspended or slowed growth among larvae which are 

 being subjected to heavy competition for the available food. Without some 

 knowledge of hatching time, temperature regime, and feeding history, there 

 appears to be no way that such larvae may be aged accurately on the basis of 

 size and/or structural development alone. 



The use of fixed stage duration estimates in predictive models, especially for 

 that stage immediately following yolk absorption, could lead to serious errors 

 in the resulting estimates of stage-to-stage mortality rates. 



ACKNOWLEDGEMENTS 



This study was performed while under contract to the U.S. Environmental 

 Protection Agency (Contract #68-03-0316). The authors wish to thank Janice 

 Steele for typing the manuscript, and Margaret Leonard for drafting the 

 figures. 



REFERENCES 



l.Albrecht, A.B. 1964. Some Observations on Factors Associated with 

 Survival of Striped Bass Eggs and Larvae. CaUf. Fish & Game 

 50(2): 100-11 3. 



2. Bayless, J.D. 1972. Artificial Propagation and Hybridization of Striped 

 Bass, Morone saxatilis (Walbaum). S.C. Wildlife and Marine Resources 

 Dept., 135 pp. 



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