arine portion has a MLW (mean low water) volume 

 of 123.4 x 10 6 m 3 , a tidal volume of 56.2 x 10 6 m 3 , 

 and a mean summer flushing time of 4-5 wk 



DAMARISCOTTA 



DAMARISCOTTA RIVER 



LOCATION MAP 



1 ,5 1 



NAUTICAL MILES 

 1 .5 1 2 



KILOMETERS 



- 44" 00' 



- 43* 55' 



43* 50' 



(McAlice 1977). The estuary is stratified near its 

 head but approaches a well-mixed condition further 

 seaward. Tides are semi-diurnal with a mean range 

 of 2.7 m and a tidal excursion of about 2.8 km (Lee 

 and McAlice 1979). 



Monthly plankton samples were collected during 

 daylight at station D7 (Fig. 1) from October 1969 

 to June 1970 and then biweekly until September 

 1977. Plankton tows were 10-15 min oblique hauls 

 with #20 mesh (76 /im) nets of 0.5 m mouth diam- 

 eter equipped with centrally mounted flowmeters. 

 Maximum depths of tows were 10-15 m (4-5 m above 

 the bottom). Boat speed was 1-2 m s -1 . Samples 

 were immediately fixed in 4% buffered Formalin 2 . 



Laboratory subsampling followed the method 

 recommended by Frolander (1968). The concen- 

 trated plankton was diluted to a known volume, 

 thoroughly stirred, and a 1 mL aliquot removed with 

 a Stempel pipette. Initial counts on samples taken 

 from June 1974 to September 1977 did not distin- 

 guish among taxa of larval bivalves. We therefore 

 took an additional subsample, determined the per- 

 centage of Mytilus in 50 bivalve larvae, and multi- 

 plied this by the total veliger abundance to obtain 

 Mytilus densities for each sampling period. 



Several key publications (Loosanoff et al. 1966; 

 Chanley and Andrews 1971; DeScweinitz and Lutz 

 1976; Lutz and Hidu 1979) containing photomicro- 

 graphs and descriptions were used to identify 

 Mytilus edulis larvae. The differentiation of Mytilus 

 edulis larvae from other mytilid larvae (Modiolus 

 modiolus and Geukensia demissa) at the straight 

 hinge stage was achieved by comparing the length 

 of the hinge line as well as total shell length and 

 height. The early and late umbo larvae of Geuken- 

 sia were easily distinguishable by their elongated 

 appearance; Mytilus larvae tended to be less 

 elongate, though pointed anteriorly (Chanley and 

 Andrews 1971). The differentiation of Modiolus 

 modiolus larvae and Mytilus edulis larvae was based 

 mainly on the characteristics described by 

 DeSchweinitz and Lutz (1976); hinge line lengths, 

 total shell length in the 95-105 ycm range, shell shape 

 of umbo stage larvae, presence of an eye spot in 

 specimens <270 yxn, and the presence of a functional 

 foot in larvae <295 \xm. Further positive identifica- 

 tion of late stage Mytilus larvae was achieved by 

 examining the hinge teeth of disarticulated valves 

 (Lutz and Hidu 1979). 



Spawning dates were estimated by subtracting the 

 approximate age of the larvae from the sampling 



69' 35' 



69'30' 



Figure 1.— Location map. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



996 



