SIMPLE MODEL FOR ASSESSING POTENTIAL LOSS 



57 



100.0 



10.0 



0.001 



0.0001 



Fig. 2 The ratio (r) of predicted to actual loss when planktonic 

 mortality comprises a specific proportion (p) of the mortality 

 assumed by the alternative model. 



The potential relationships of Sea to Sq can be examined by 

 comparing Sea to Sq values calculated with the Leslie Matrix 

 (Vaughan and Saila, 1976). Table 3 shows the results of comparisons 

 for seven species [I used the method described by Horst (1978) to 

 estimate the range of Sea! » along with the quantity r, the ratio of 

 predicted to actual loss. The information in Table 3 indicates that 

 Sea is highly variable in its ability to estimate Sq , but it appears that 

 in most cases use of Sea to approximate Sq will not result in large 

 overestimates of impact. 



DISCUSSION 



In proposing a revised form of the equivalent-adults model, I 

 have introduced several new assumptions that must be considered 

 when using the model: 



1. Survival corresponds to an exponential model during all 

 planktonic life stages. 



2. All mortality during the first year of life occurs during the 

 planktonic life stages. 



3. Vulnerability of plankton to entrainment remains constant 

 throughout the planktonic life stages. 



4. Plankton that are the victims of natural mortality are not 

 entrained. 



5. Survival from egg to adult is an approximate estimator of 

 first-year survival, Sq . 



Assumption 1 is relatively straightforward and requires no 

 discussion, and assumptions 2 and 5 were examined in the sensitivity 

 analysis. 



