FISHERY BULLETIN: VOL. 86, NO. 3 



Table 3.— Size-specific survival rates for marked 

 Mya arenaria from the Stonington population. P 

 = probability of an individual from size-class / sur- 

 viving one year; N^ = number of live clams; Nqq 

 = number of dead clams sfiowing growth. 



Table 4.— Size-specific survival rates for marked 

 Mya arenaria from the Westport population. P = 

 probability of an individual from size-class / surviv- 



ing one year; 



Na = 



number of live clams; N, 



DG - 



number of dead clams showing growth. 



Size-class Size (mm) 



N^ 



N. 



DG 



of surviving one year for adult clams at Stonington 

 (30 -1- mm in shell length) is significantly higher than 

 at Westport (20+ mm in shell length) (P < 0.001, 

 X^ test). 



Age-specific survivorship estimates (Table 5) were 

 calculated by assuming that 20-30 mm clams at 

 Stonington survivied with the same probability as 

 30-40 mm clams and that 90-100 mm clams at Ston- 

 ington survived with the same probability as 80-90 

 mm clams and application of Equation (4) using the 

 empirical distributions in Appendix Tables 1 and 2. 



Table 5. — Age-specific survival rates for marked 

 Mya arenaria from the Westport and Stonington, 

 CT populations. P^ = probability of surviving 

 from age-class x to age-class x + ^. 



Age-class 



(yr) 



Westport 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 



0.6390 

 0.6442 

 0.6625 

 0.6680 

 0.6595 

 0.6422 

 0.6128 

 0.5991 

 0.5021 



Population Dynamics 



The age-specific survivorship and fecundity sched- 

 ules for M. arenaria are combined in Hfe table form 

 in Tables 6 and 7. Since rates of larval survivorship 

 are difficult to measure for species with planktonic 

 larvae, simplifying assumptions are necessary for 

 estimating survivorship probabilities of larvae (age 

 0). In order to complete the life tables the equilib- 

 rium settlement rates (rj were calculated using 

 the method of Brousseau et al. (1982). Our choice 

 of r^ implies that the net reproductive rate, Rq, 

 which is defined by Rq = ^l^m^, were Ij = sur- 

 vivorship and m_c = fecundity, equals one for both 

 populations. This is not meant to imply however, 

 that the populations studied here are considered to 

 be in equilibrium. Rather, it is used simply as a 

 theoretical construct in which to examine possible 

 consequences of differing fecundity and mortality 

 schedules on the two populations of M. arenaria. 



Table 6.— Life table for the Westport, CT Mya arenaria 

 population, assuming equilibrium conditions, i^ = 

 survivorship to beginning of age interval x, or /^_, x 



Pj, . , when X > 1 ; 



m^ = fecundity during age interval x. 



1 /, = r, X (probability of surviving from 2 months to 1 year). 



Table 7.— Life table for the Stonington, CT Mya are- 

 naria population, assuming equilibrium conditions. 1^ 

 = survivorship to beginning of age interval x, or /,_, 

 X P^_, when x > 1; m^ = fecundity during age inter- 

 val X. 



' /, = r^ X (probability of surviving from 2 months to 1 year). 



572 



