TABLE 12. Annua] mean densities (number per 1000 m ) of lobster larvae in entrainment samples 

 during their season of occurrence and annual entrainment estimates with 95% C.I. for MNPS from 

 1984 through 1987. 



Mean densities are calculated as the S-mean (see Delta Distribution Section and Pennington 

 1983). 



Unit 3 began commercial operation 



density of larvae in the cooling waters and total 

 cooling water volumes; since Unit 3 requires al- 

 most double the cooling water demand of Units 

 1 and 2 combined, a doubling of the estimated 

 number of lobster larvae entrained was expected 

 when all units were operating during the larval 

 season. Projecting the impact associated with 

 lobster larvae entrainment to the population level 

 (adult lobsters) was difficult due to the lack of 

 knowledge regarding larval and post-larval stages 

 of lobsters (Phillips and Sastry 1980). Given that 

 lobsters require several years of growth to reach 

 a trappable size, our studies of adults would not 

 detect 3-unit entrainment effects until 5-6 years 

 after an impact occurred. 



During 1986, 6.5% and in 1987, 3.8% of the 

 lobster larvae survived after passing through the 

 plant's cooling water system suggesting that en- 

 trainment mortality may be lower than the as- 

 sumed 100%. Similar findings at other power 

 stations have been reported. ColUngs et al. (1981) 

 reported 14"/o survival for lobster larvae (Stage 

 II) collected at the Canal Electric Company, Sand- 

 wich, MA. 



Impingement 



Impingement of lobsters on the Unit 1 and 2 

 intake screens has been summarized for the period 

 1975 to 1985 in NUSCO (1987a). Throughout 

 these studies several measures were investigated 

 to mitigate impingement losses, including the use 

 of underwater barriers, acoustic and light deter- 

 rents and more recently fish return systems 

 (sluiceways). In 1983, a sluiceway system was 

 installed in the Unit 1 intake structure which re- 

 turned 100% of the lobsters caught on the screens 

 back to Niantic Bay. A sluiceway was also con- 

 structed at Unit 3 and operated during 1986 and 

 1987 (NUSCO 1987b). 



The estimated number of lobsters impinged at 

 Unit 2, which does not have a sluiceway, was 676 

 and 825 in 1986 and 1987, respectively (Table 

 1 3). These values were within the range of values 

 reported for impingement at Unit 2 (261-1220). 

 The impingement of lobsters was highest during 

 the summer months and coincided with peak 

 catch in traps (NUSCO 1987a). 



The mean sizes of lobsters impinged during 

 1986-87 were 55.7 and 55.8 mm CL, respectively, 

 which were within the range of pre-operational 

 values 48.6 to 64.9 mm CL and continued to be 



Lobster Population Dynamics 



139 



