. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . 50 100 miles I I 175 170 165° 160° Figure 66-19. Qualitative distribution of Clinocardium ciliatum taken in the southeastern Bering Sea by van Veen grab (Federetal. 1980). recruitment apparent in individual samples. Using the number of individuals calculated from the curve rather than the actual catch, the percent mortality at each age is estimated. The numbers at age from the curves are calculated using the expression: where N = number of clams, z = mortality coefficient, t = time, t +
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . 50 100 miles I I 175 170 165° 160° Figure 66-19. Qualitative distribution of Clinocardium ciliatum taken in the southeastern Bering Sea by van Veen grab (Federetal. 1980). recruitment apparent in individual samples. Using the number of individuals calculated from the curve rather than the actual catch, the percent mortality at each age is estimated. The numbers at age from the curves are calculated using the expression: where N = number of clams, z = mortality coefficient, t = time, t + 1 = time at the next year, and the constant e = The mortality curves were drawn by a Honeywell 66/40 computer, a modification of Gruffydd's technique (1974) in which the curves were plotted by eye on semilog paper. RESULTS Growth Increases in shell length of mm/yr occur in the small species Nucula tenuis, Nuculana fossa, Yoldia amygdalea, and Macoma calcarea (Tables 66-12 to 66-15, Figs. 66-27 to 66-30, 66-34 to 66-37), and mm/yr for the larger clams Spisula polynyma (Hughes and Bourne, Chapter 67, this volume) and Tellina lutea (Tables 66-16 and 66-17, Figs. 66-31 to 66-33, 66-38, and 66-39). The small clams are relatively long-lived; N. tenuis and N. fossa reach 9 years of age and 13 and 21 mm in shell lengths, respectively, Y. amygdalea reach 13 years and 32 mm, and M. calcarea 11 years and 49 mm (Figs. 66-34 to 66-37). The larger clams grow at faster rates and seem to live even longer; S. polynyma and T. lutea live 14 years and attain 135 and 83 mm in shell length, respectively (Figs. 66-38 and 66-39). Hughes and Bourne (Chapter 67, this volume) have reported a 19-year-old S. polynyma at 123 mm. No radical differences in size and age within each of the six species of bivalves examined were observed relative to their point of collection on the southeastern Bering Sea shelf (Tables 66-11 to 66-17, Fig. 66-26). Age composition The age analyses of those
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