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 (11). 
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 
1. Albrecht, A.B. 1964. Some Observations on Factors Associated with 
Survival of Striped Bass Eggs and Larvae. Calif. Fish & Game 
50(2): 100-113. 
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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