Table 17. Annual impingement estimates ' for lobster collected at Units 1 and 2 from 1975 to 1985, 



Unit 1 



1975 734 



1976 479 



1977 240 



1978 245 



1979 323 



1980 368 



1981 665 



1982 938 



1983 999 



1984 b 



1985 b 

 Total 4991 6368 11359 



' Values for the 1975-76 estimates are based on 7 days of sampling per week. The 1977-83 values are 

 based on 3 days of sampling per week and are extrapolated based on flow rates to represent the estimated 

 total number impinged. 

 Unit 1 sluiceway began operating December 1983. 



The mean sizes of lobsters impinged during the period 1975-85 have ranged from 48.6 to 64.9 mm 

 CI, and were smaller than the trap catch values (NUSCo 1982, 1983, 1984, 1985, 1986). Smaller lobsters 

 may enter the screen house through the course bar racks more readily than larger lobsters which are seldom 

 impinged. Since 1982, when we began recording the sex of impinged lobsters, male to female ratios ranged 

 from 1.0:0.47 to 1.0:0.58 and were similar to those reported for the inshore Jordan ("ove and Intake 

 stations (NUSCo 1982, 1983, 1984, 1985, 1986). The percentage of culled lobsters was always greater in 

 impingement samples (30-50%) when compared to trap catch values (wood 9-17%; wire 10-16%) and is 

 probably related to the high pressure (80 psi) wash used to remove debris from the screens (NUSCo 1982, 

 1983, 1984, 1985, 1986). 



A fish return system (sluiceway) was constructed at Unit I and began operating in December 1983. 

 Prior to the sluiceway operating at Unit 1, and presently at Unit 2, 100% mortality occurs to organisms 

 impinged at MNPS on non-impingement sampling days. On those days that impingement counts were 

 made, survival of lobsters impinged at Units 1 (1975-83) and 2 (1975-1985) ranged from 64-80% (NUSCo 

 1982, 1983, 1984, 1985, 1986). Generally, highest mortality of lobsters occurred during the peak molting 

 period when lobsters are soft and easily damaged and during the later summer months when water 

 temperatures are highest (NUSCo 1982, 1983, 1984, 1985, 1986). The design and operation of the Unit 

 3 traveling screens should improve survival and minimize damage to lobsters associated with the 

 impingement process at MNPS. A low pressure (10 psi) screen wash will be used to remove organisms 

 from the screens. The organisms are carried from a fish trough to a sluiceway which returns the organisms 

 back to Niantic Bay. 



34 



