11-103 



Evaluating total entrainment losses (cropping) under worst- 

 case conditions, i.e., assuming 100% mortality, and using seasonally 

 averaged egg and larval densities, reported for the years of maximum 

 abundance, the impact in terms of numbers of individuals killed may be 

 roughly estimated by taking the "worst case" conditions and multiplying 

 the average densities by the demand of the cooling water intake for the 

 entire period of egg or larvae occurrence. Results of such computations 

 are shown for the 16 representative species in Table 11-3. 



Estimates of the nximber of eggs and larvae entrained during a 

 year of maximum abundance range from several tens of thousands to 

 several hundred million, depending on the species in question. Though 

 any attempt to interpret such losses in terms of the ultimate impact on 

 the adult population is imprecise, it is useful to compare these approx- 

 imate entrainment losses with those that might be expected to result 

 from natural causes — starvation, predation, and disease. Leggett 



(1969) estimated a 0.001% survival rate from egg to adult for the Amer- 

 ican shad on the Connecticut River? similarly, Kissil (1974) reported 

 0.004% survival from eggs to sea-r\inning juvenile alewives. Winter 

 flounder, which at about 8C require 49 days to develop from egg to 

 juvenile (Laurence, 1975) undergo natural mortality of 20% per day as 

 early larvae and 4% per day as post larvae (Pearcy, 1962) . Pearcy 



(1962) estimated total mortality for larval and juvenile stages of 

 winter flounder at 99.98-99.99%. If such survival ratios are generally 

 applicable to other species, then the loss of 10 inillion eggs through 

 passage through a power plant cooling water system would be equivalent 

 to the loss of 10 to 14 thousand juvenile to adult fish, 



Jones and Hall (1973) developed a computer simulation model 

 for the growth and survival of haddock {Melanogrammus aeglefinus) 

 larvae which indicated a mortality rate of 10% per day. A comparable 

 modeling effort by Gushing and Harris (1973) , showed a mortality of 5% 

 per day (80% per month) for plaice {Pleuronectes platessa) . Utilizing 

 these estimates, and assuming a hypothetical average larval density of 1 

 per m , the number of larvae lost in nature per day throughout New Haven 



o o 



Harbor (volume at mean sea level, 1.2 x 10 m ) would be 6 to 12 million. 



