FISHERY BULLETIN: VOL. 80. NO. 1 



Modified exponential and logistic growth 

 equations were fitted to mean back-calculated 

 lengths at age, from the July 1978 samples (Table 

 3), using the asymptotic regression and nonlinear 

 least squares computer programs BMD06R and~ 

 BMD07R, respectively (Dixon 1977; Fig.. 3). 

 Few aged shells were as large as those recap- 

 tured (Tables 2, 3). Growth functions generated 

 from aging data were thus extrapolated to the 

 size range of recaptured specimens and results 

 compared with annual growth increments pre- 

 dicted from mark-recapture (Figs. 2, 3). An age- 

 size point necessary to initiate the mark-recap- 

 ture growth function was computed from growth 

 equations fitted to age-length data generated in 

 shell banding experiments; the mark-recapture 

 equation was then iterated to encompass most 

 shell lengths present at the marking site (Figs. 

 4,5). 



SL„,= 20811 +09802 SL 



60 



50 



40 



£ 30 



ui 



X 



C/5 



20 



10 



SL = 7568-81.31 (0.9056) 



AGE 



o OBSERVED 



■• PREDICTED 



6 8 10 12 



AGE (YEARS) 



14 



16 



18 



Figure 3.— Observed and predicted shell lengths at age for 

 small ocean quahogs sampled during July 1978 near lat. 40°25' 

 N. long. 72°24'W. in the Middle Atlantic Bight. 



Length-Weight 



Shell length-drained meat weight relation- 

 ships were computed for samples taken during 

 August 1979 and February 1980. Laboratory 



28 



SHELL LENGTH 

 MEAT WEIGHT 



10 20 30 40 50 60 



AGE I YEARS) 



80 90 100 



Figure 4.— Predicted shell lengths (millimeters) and drained 

 meat weights (grams) at age for ocean quahogs at lat. 40°25' N, 

 long. 72°24'W, in the Middle Atlantic Bight. Growth in length 

 is described by an equation derived from studies of external 

 banding patterns of small individuals (left of dot), and the 

 Ford-Walford equation from mark-recapture data (right of 

 dot). Weights at age are derived by applying the overall length- 

 weight equation presented in Table 5 to calculated mean 

 lengths at age. 



and statistical methods are given in Murawski 

 and Serchuk (1979). Equations for recaptured 

 and unmarked specimens from August 1979 

 were compared by covariance analysis to assess 

 effects of marking (Table 4). Presumably, if 

 physiological processes of the animal were sig- 

 nificantly disrupted by the marking procedures, 

 the adjusted mean of the length-weight equation 

 might be statistically lower than that of controls. 

 Seasonal variability in length-weight was in- 

 vestigated by comparing summer and winter 

 equations (Table 5). 



RESULTS AND DISCUSSION 



New shell growth of recaptured individuals 

 was clearly discernible in small specimens (<70 

 mm) not only at the mark, but all along the 



Table 4.— Ocean quahog shell length-meat weight regression 

 equations, and analysis of covariance for marked and un- 

 marked individuals sampled at lat. 40°25' N, long. 72°24' W, 

 in the Middle Atlantic Bight, during August 1979. 



n.s. = P>0.05. 



