FISHERY BULLETIN: VOL. 81. NO. 4 



TABLE 6. — Regression statistics for microgrowth increment counts on days in monitored 

 growth periods of short- term experimental Mercenaria mercenaria a = Y-intercept, b = 

 regression coefficient (slope); t s = Mest statistic for// ; P = 1.00 vs. H : : ft ?= 1.00; r = 

 correlation coefficient. 



Group 



Collection 

 period 



(V 



6±95% C.L 1 



Tl Summer 1980 12 



T and Tl Spring 1980 to 



summer 1981 58 



T and Tl Spring to 



fall 1980 31 



TandTI Winter 1980 to 



summer 1 981 27 



1 C.L = confidence limits. 



I40 



I20 - 



I00 



CO 



I- 



U 



or 

 o 



20 40 60 80 I00 



DAYS (0 = 30 MAY I980) 



1 20 



Fic.l'RE 3. — Average (horizontal bar) and range (vertical bar) of the 

 number of microgrowth increments formed by Tl series hard clams, 

 Mercenaria mercenaria, during summer 1980 after induced growth 

 disturbance of 29-30 May 1980. Zero on abscissa equals 30 May 

 1980. Solid line = regression; dashed lines = ±9595 confidence 

 limits on regression coefficient (Table 6). 



increment during each solar day for the 4 summer 

 months. 



T and Tl Series, From 16 October 1979 



obscure the fact that 85% of hard clams collected 

 during or after winter 1980 had distinct winter 

 growth cessation marks within the light band at the 

 shell margin (as in Figure 2D). Growth cessations of 

 varying durations should reduce regression (6) and 

 correlation coefficients (r) in an analysis based on 

 counts from hard clams collected during or after win- 

 ter 1980 compared with one based on counts from 

 hard clams collected from spring through fall 1980. 

 Results from such analyses (Table 6; Fig. 4) revealed 

 neither significant differences between the two re- 

 gression coefficients (F s = 0.50, P> 0.25) or signifi- 

 cant differences of both from 1.00. However, con- 



600- 



500- 



CO 400- 

 Ll) 



UJ 



or 

 o 



300- 



— 200- 



100- 



SPRING - FALL 1980 



WINTER 1980- 

 SPRING 1981 



r 1 1 



200 300 400 500 600 700 



DAYS (0= 16 OCTOBER 1979) 



T and Tl hard clams collected from spring 1980 to 

 summer 1981 also tended to form one increment for 

 each solar day of activity. Regression analysis 

 revealed a strong linear relationship between num- 

 bers of increments formed and days since 1 6 October 

 1979 (F= 177.25, P< 0.001; Table 6). Furthermore, 

 the regression coefficient was not significantly dif- 

 ferent from 1.00 (Table 6). These statistics tend to 



FIGURE 4. — Average and range (as in Figure 3) of the numbei of mi- 

 crogrowth increments formed by T and Tl series hard clams, Mer- 

 cenaria mercenaria, from fall 1979 to summer 1981 in hard clams 

 collected after April 1980 to June 1981. Increments were counted 

 from growth disturbance caused by transplantation in October 

 1979. Zero on abscissa equals 16 October 1979. Regression 

 analyses based on 3 1 hard clams collected from spring to fall 1980 

 and 27 clams collected from winter 1980 to summer 1981. Solid and 

 dashed lines as in Figure 3 (see also Table 6). 



704 



