To predict the long-term effects of larval entrainment at MNPS, an impact assessment model for winter 

 flounder is currently under development, which includes hydrodynamics and population dynamics 

 submodels. The function of the submodels is the estimation of the fraction of total larval production lost 

 to entrairmient at the plant and the measurement of any resulting population changes, respectively. A 

 newer, more accurate and detailed hydrodynamics submodel is under development at the Massachusetts 

 Institute of Technology. Larval behavior will be simulated to correspond more realistically to observations 

 made in the field. A stochastic age- structured population submodel will incorporate the three-parameter 

 stock-recruitment relationship, which includes a measure of compensatory mortality and the introduction 

 of realistic environmental variability. 



Results from both larval analyses and the three-parameter stock-recruitment relationship showed that 

 year-class strength was related to events in the early life history stages, with colder winters associated with 

 better reproductive success. Greatest winter flounder mortality took place during Stage 2 of development, 

 during which density- dependent mortality probably occurred. 



Exposure Panel Program 



The Exposure Panel Program was designed to assess the effect of Millstone Nuclear Power Station (MNPS) 

 on the abundance and distribution of marine woodborers, and the associated rate of wood-loss. To achieve 

 this objective, fouling organisms, woodborer densities and wood-loss arc being monitored at five dock sites 

 and three thermal plume sites (100, 500 and 1000 m from the quarry discharge). Results presented in this 

 report cover the initial period of 3-unit operation and provide a comparison to data collected during 2-unit 

 operation. 



The fouling community on wooden exposure panels showed no clear response to 3-unit operation, but 

 this community has correlated negatively with shipworm recruitment throughout the study. Fouling 

 assemblages continue to be diverse, and the abundance and distribution of the component species remain 

 patchy. Patterns of abundance and distribution of several prevalent fouling species were consistent between 

 2-unit and 3-unit operational periods, i.e., Cryptosula pallasiana and Laminaria saccharina at sites not 

 influenced by the undiluted thermal plume and Mylilus edulis within tlie undiluted plume. Changes in 

 the densities of juvenile barnacles and Balanus crenalus between the two operational periods were attributed 

 to a sliglitly later set during the 3-unit operational period. The large percentage of cover and density of 

 Balanus balanoides, an intertidal barnacle on subtidal panels during 1986 and 1987, were similar to incidental 

 occurrences reported for this species in 1970 and 1971. 



Shipworm densities showed the most consistent differences between 2-unit and 3-unit operation. During 

 the furst six-month collection period of 3-unit operation (May to November 1986), there was an increase 

 in density of the shipworm, Teredo navalis, and an increase in the amount of wood-loss at the White 

 Point and Fox Island sites. At our reference site. Giants Neck, shipworm density decreased. The largest 

 increases in shipworm densities and wood-loss occurred in panels at our undiluted effluent sites during 

 3-unit operation. These increases were caused by Teredo hartschi, a non-native species collected at efQuent 

 sites since 1975. The reason for this change is unclear. Because water temperatures at our effluent sites 

 remain very similar between 2-unit and 3-unit operating conditions, some other mechanism was responsible 

 for these observed increases. Possibl> , altered water circulation patterns in the effluent quarry allowed 

 more larvae to reach these panels, which were suspended more than I m above the bottom. 



Panels placed at 100, 500, and 1000 m from the quarry cuts showed decreased recruitment of T. navalis 

 at increasing distances from the quarry cuts. This was consistent with past results. Teredo bartschi was 



Executive Sunmiary 



