TABLE 11. Summary of lobster larvae entrainment data from 1984 to 1987. 



Stage I 



Stage II 



Stage III Stage IV 



Total 



Day 



Night 

 lota! 



Day 

 Night 

 Total 



Day 



Night 

 Total 



Day 



Night 

 Total 



samples was high, similar to findings by other 

 researchers working with lobster larvae (Bibb et 

 al. 1983; Lux et al. 1983; Blake 1984). The con- 

 tagious distribution of lobster larvae has been as- 

 sociated with surface water circulation patterns 

 (Fogarty 1983), which generate sea surface 

 "fronts". These fronts, visible on the surface wa- 

 ters as "scum", "foam", or "slick" lines, occur in 

 the vicinity of MNPS, and were reported to con- 

 tain high densities of planktonic organisms, in- 

 cluding lobster larvae (Cobb et al. 1983; M. Blake 

 personal communication). 



Night samples contained more larvae than day 

 samples in 3 of the 4 study years. This may be 

 due to the design of the intake structures, which 

 have curtain walls extending about 2 m below 

 MLW. This means that cooling water is drawn 

 from 2 m below the surface. Since the early 

 stages of lobster larvae are photopositive and dis- 

 perse from surface waters during darkness 

 (Templeman 1939), they are more susceptible to 



entrainment at night regardless of tidal stage. 

 However, during daylight hours lobster larvae 

 predominate in surface samples (Fogarty 1983; 

 Fogarty and l^wton 1983). Therefore larvae 

 avoid entrainment during the day due to their 

 photo-behavior and the intake structure design. 



The density of lobster larvae in the MNPS cool- 

 ing waters was estimated as the 5-mean (see Delta 

 Distribution Section of this report and also 

 Pennington 1983). The annual 5-mean density 

 (number per 1000 m ) of lobster larvae collected 

 in entrainment samples was higher in 1986 (0.88) 

 and 1987 (0.63) than 1984-85 densities (0.42-0.43, 

 Table 12). The estimated number of lobster 

 larvae entrained through the MNPS cooling water 

 systems in 1986 and 1987, was 548,635 and 

 304,694, respectively. The higher estimates in 

 1986-87, relative to 1984 and 1985 values of 

 79,511 and 138,820, respectively, were related to 

 the fact that Unit 3 began operating in 1986. 

 Fntrainment estimates were based on both the 



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