TABLE 5. The seasonal 5-mean density (no. per 500 m ) of abundant fish egg taxa collected at EN by report period (June- 

 May)^ 



Taxon 79-80 80-8! 81-82 82-83 83-84 84-85 85-86 86 



Taulogolabnis adspersus 

 Tautoga onitis 

 Anchoa spp. 



'Data seasonally restricted to May 23-July 22 for Tautogolabrus adspenrus, to May 24- August 19 for Tautoga onitis, and to 

 June 16-Ajgust 4 for Anchoa spp. . 



Data seasonal restricted to July-September for Anchoa spp. , to March-June for Pseudopleuronectes americanus, to December- 

 April for Ammodytes americanus , and to February-May for Myoxocephalus aenaeus. 



Althougli impingement has decreased at Unit 2, 

 potential impacts could still occur there which 

 would go undetected because of the elimination 

 of routine monitoring. Therefore, a procedure 

 was established so that operations personnel will 

 examine and record all large impingement events 

 (over 300 fish m a 24-hour period). Mitigative 

 measures to reduce impingement impacts from 

 MNPS have been incorporated and include the 

 addition of a fish-return sluiceway at Unit 1 and 

 continued modification of the fish-return system 

 at Unit 3 to increase its efficiency. 



Ichthyoplankton 



Ichthyoplankton studies at MNPS have pro- 

 vided entrainment estimates, seasonal density in- 

 dices, and species composition. Over 50 taxa of 

 ichthyoplankton have been collected (Appendix 

 I). The additional mortality due to entrainment 

 could affect local fish populations since natural 

 ichthyoplankton mortality rates are one of the 

 most important controlling factors of adult fish 

 stock abundance (Gushing and Harris 1973; Ban- 

 nister et al. 1974; Gushing 1974; May 1974; 

 DeAngelis et al. 1977). 



S-mean densities were calculated for the most 

 abundant fish egg and larval taxa entrained (Tables 

 5 and 6). Gunner eggs and anchovy larvae have 

 consistently been the most abundant taxa col- 

 lected. For all dominant larvae collected at EN, 

 there appeared to be a general pattern of high 

 abundance in the late 1970s or early 1980s fol- 

 lowed by a decline to present levels that were 

 similar to the mid 1970s. Gunner, tautog, and 

 anchovies have accounted for over 93% of eggs 

 collected at EN; and anchovies, winter flounder, 

 sand lance, and grubby have accounted for over 

 85% of the larvae collected at EN (Table 4). 

 These taxa were selected as potentially impacted 

 and discussed in greater detail following this sec- 

 tion, except for winter flounder (see Winter Floun- 

 der Studies section). 



ITie dominant ichthyoplankton taxa collected 

 at EN were compared to taxa collected in the 

 trawl and seine programs. Except for winter floun- 

 der, few adults of abundant ichthyoplankton taxa 

 were collected by trawls or seines. Adult ancho- 

 vies, cunner, and tautog apparently were not very 

 susceptible to our demersal trawl or shore-zone 

 seine sampling. Adult abundance, or stock re- 

 productive capacity, for these three taxa was prob- 

 ably best measured by seasonal egg abundance. 

 The early life history stages of scup, windowpane, 

 skates, and silversides were rare in ichthyoplankton 



266 



