METHODS AND MATERIALS 



The samples on which this report is based were collected in two loca- 

 tions in Narragansett Bay (fig. 1) s Wickford Harbor, approximately 1 

 mile long, with an irregular shoreline and an average depth at mean low 

 water of 2 to 3 feet 5 and Greenwich Bay, rectangular in shape about 2-1/2 

 miles long and 1 mile wide, with an average depth of about 10 feet. 



Salinities in both places are usually within the 25 to 30 parts per 

 thousand range. Current velocities are uniformly low, the greatest being 

 about 1 knot. Many of the plankton samples and other supplementary obser- 

 vations were taken by Thomas F. Kane, Fishery Aid. 



All samples from Greenwich Bay were taken with a rotary pump powered 

 by a small gasoline engine. Wickford Harbor samples were taken with the 

 pump when possible and with a 12-quart bucket otherwise. When time and 

 facilities permitted, at least two samples, surface and bottom, were obtained, 

 and occasionally other levels were also sampled. A sample consisted of 35 

 to 50 gallons of water strained through a No. 18XXX net with mesh openings 

 approximately 75 microns on a side. The net was equipped with a detachable 

 plankton bucket. The samples were transferred to plastic-topped jars, 

 brought back to the laboratory, and preserved with 1 percent formalin 

 neutralized with borax. 



Each sample was concentrated to a definite volume, either 10 or 20 ml., 

 depending upon the abundance of material, and 1 ml. was removed with a 

 pipette. This subsample was placed in a Sedgewick-Rafter cell and the 

 larvae were counted and assigned to one or more of the following size cate- 

 gories; (1) Up to 135 microns, greatest diameter, or straight-hinge stage; 

 (2) 136 to l6o microns, or early umbone stage; (3) l6l to 185 microns, or 

 medium umbone stage; and (h) 186 microns and up, late umbone or larvae 

 approaching setting stage. This size grouping was designed for Venus 

 larvae, but is serves adequately for Mya larvae also. There is evidence 

 from the literature that bivalve larvae tend to patchiness in their verti- 

 cal and horizontal distribution. Because of this it would seem that the 

 level with the highest count of larvae in its sample would best represent 

 the degree of spawning success in the area. Consequently the samples with 

 the highest counts for each of the two kinds of larvae from all levels 

 sampled at any one station were taken as representing that station on t hat 

 particular date. 



In this report, only categories 1 and h are presented. The graphs 

 were prepared as follows: The average highest sample count for the size 

 category under consideration was obtained for each week and was plotted 

 as a bar covering the middle 3 days of the week. For -example, during the 

 week of June 11-17, 1°50, six samples were taken at the Wickford Habor 

 station. Four samples, of 35 gallons each, contained Mya larvae of size 

 category 1 as follows; 5,960, 5,160, 5,h00, and 2,960. The average number 

 per sample is It, 870. On figure 3 this is plotted as a bar covering June 13, 

 lU, and 15. Five samples, of 35 gallons each, contained Venus larvae of 



