A SIMPLE MODEL FOR ASSESSING 

 THE POTENTIAL LOSS OF ADULT FISH 

 RESULTING FROM ICHTHYOPLANKTON 

 ENTRAINMENT 



W. PETER SAUNDERS, JR.* 



Environmental Research and Technology, Inc., Concord, Massachusetts 



ABSTRACT 



A mathematical model for estimating potential survival of fish eggs and larvae to 

 reproducing adults is examined in the context of predicting the potential loss 

 from power-station entrainment. It is demonstrated that violating one 

 assumption of the model can result in gross underestimates of potential adult 

 loss. High rates of natural mortality occurring during the egg and larval life stages 

 are considered in relation to the assumption that all exploitation by the powder 

 plant occurs instantaneously at spawning or hatching. The sensitivity of 

 potential loss estimates to various time— mortality-rate regimes is examined on 

 the basis of the natural mortality rates observed in young life stages of several 

 species. An alternative model is proposed, and its sensitivity to underlying 

 assumptions is examined. This model is shown to consistently overestimate loss 

 of equivalent adults. The magnitude of the overestimation depends on 

 species-specific conformity of the model assumptions to actual planktonic 

 mortality and first-year survival. 



Many aquatic species that produce planktonic eggs and/or larvae have 

 very high mortality of the young organisms. Of the many thousands 

 of offspring initially produced, only a few individuals survive to 

 reproductive maturity. Since we are usually familiar with the portion 

 of a population potentially subject to exploitation by a fishery, the 

 entrainment loss of large numbers of planktonic young may be more 

 meaningful in the impact assessment process if considered in relation 

 to the numbers of reproducing adults that could potentially result 



♦Current address: Massachusetts Cooperative Fisheries Research Unit, 

 University of Massachusetts, Amherst, Mass. 



49 



