ENVIRONMENT AND GROWTH OF THE SOFT CLAM 



283 



Table 1. — Average growth of clams in test areas 

 [Values based on samples taken November 1951 to March 1952] 



Tested in— 



Soil type 



Transplanted from- 



Soil type 



Mean 

 growth 



Proportion 



recovered 



alter 1951 



growing 



season 



Bedroom Cove. 



Sagadahoc Bay 



Rohinhood Cove. 



Falls Cove 



Plum Island Sound 



Sandy silt. 



Sand 



Silt 



Gravelly silt . 

 Sandy silt 



Western Beach 



Meetinghouse Cove. 



Sagadahoc Bay 



Bedroom Cove 



Western Beach 



Meetinghouse Cove. 



Sagadahoc Bay 



Bedroom Cove 



Western Beach 



Meetinghouse Cove.. 



Sagadahoc Bay 



Bedroom Cove 



Western Beach , 



Meetinghouse Cove. 



Falls Cove 



Western Beach 



Meetinghouse Cove. 

 Plum Island Sound - 



Sand 



Silt- 



Sand-- 



Sandy silt 



Sand-. 



Silt 



Sand--- - 



Sandy silt 



Sand-- - 



Silt --.. 



Sand.-- 



Sandy silt 



Sand 



Silt 



Gravelly silt. 



Sand 



Silt -- 



Sandy silt 



Mm. 

 3.99 



6.18 

 2.42 

 3.55 

 17.09 

 20.30 

 14.48 

 18.36 

 14.69 

 18.03 

 11.74 

 16.21 

 2.26 

 3.87 

 2.85 

 ' 19.03 

 > 19. 14 

 ' 19. 69 



Percent 



56.0 



50.7 



56.7 



50.0 



38.7 



24.7 



67.3 



40.7 



3.2 



7.6 



5.4 



5.6 



31.3 



66.7 



6.5 















' Growth at Plum Island Sound is based on shell readings of clams that were dead at time of recovery. 



To increase the geographical scope of the experi- 

 ment, additional experimental plots were estab- 

 lished in Robinhood Cove and Falls Cove in 



-Maine, and in Plum Island Sound in Massa- 

 chusetts (fig. 3). The design of the experiment is 

 summarized in table 1. 



EXPERIMENTAL PROCEDURE 



Soft clams with an approximate lengtii of 25 

 mm. were used in the experiment. This initial 

 length was chosen because clams near this size 

 were available in all areas and because (the 

 growth rate of small clams being rapid) differences 

 between areas or plots would be greater than if 

 large clams had been used. Another reason for 

 choosing clams about 25 mm. long was that growth 

 rates would be comparable with those listed by 

 Belding (1930). 



Each clam was marked with Volger's opaque 

 ink to ensure identification of origin. Previous 

 experiments have shown that this ink remains 

 visible on transplanted clams for a period of 2 to 4 

 years. Origins were designated by symbols in 

 red or black ink so placed as to cover check marks 

 on the shells that niiglit later be confused with the 

 planting check. Care was taken to avoid injury 

 from contact of the ink with the mantle or other 

 soft parts. 



Clams from each origin were planted in a 

 separate row containing 13 plots spaced 1 yard 

 apart. Twelve of these plots were 1 stjuare 

 foot in area and contained 50 clams each, for 

 monthly .samples. The thirteenth plot in each 

 row was approxinuitely 4 square feet in area and 

 contained a reserve supply of about 200 clams. 



409441 O— 57 2 



The rows were parallel, 1 yard apart, and so 

 located that all plots were at the same tidal level 

 and were exposed to the same tidal current. All 

 clams were carefully inserted part way into the 

 substrata to prevent them from being washed 

 away before they became established in the 

 sediment. In discussion of the experiment, each 

 row containing clams from a single origin is termed 

 a "group". 



One plot from each row in Sagadahoc Bay and 

 in Bedroom Cove was dug each month during 1 

 year. The high mortality of test clams in the 

 other experimental locations prevented adequate 

 sampling during the entire year, but monthly 

 samples were taken as long as survival permitted. 



At the time of recovery, all clams were meas- 

 ured to the nearest millimeter with vernier 

 calipers for planted length and total length. The 

 planted length was determined by measuring the 

 length of clams at the check mark on the shell 

 caused by transplanting. Mean growth for each 

 plot was computed from the planted and total 

 lengths. Summaries of growth, by montlis. in 

 the five test areas are given in appendix A; the 

 mean growth for each area, based on select "d 

 samples, is shown in table 2. 



