FISHERY BULLETIN: VOL. 71, NO. 3 



dissection microscope. The patterns created by 

 the radial sculpture and the concentric growth 

 lines of the valves are invaluable aids for 

 aging P. staminea by the annular method 

 (Figure 3). 



During the winter increase in shell size is 

 negligible, and growth at the shell margin 

 consists of a series of closely spaced concentric 

 lines which form a winter annulus. Spring 

 growth results in a progressively increasing 

 distance between these lines; as summer pro- 

 gresses the distance between these lines grad- 

 ually decreases until a new annulus is formed 

 the following winter. True annuli extend from 

 near the umbo anteriorly and merge with the 

 hinge structure posteriorly. False checks may 

 also appear as an aggregation of fine concentric 

 lines; however, such checks generally fail to 

 merge dorsally, and do not fit within the pattern 

 of gradually increasing and decreasing distances 

 between the concentric growth lines mentioned 

 above. 



Size-frequency distribution histograms can- 

 not be used to accurately age P. staminea from 

 Galena Bay (Figure 5). The individual dif- 

 ferences in yearly growth within age groups, 

 even when taken from a single 0.25-m'- plot, 

 result in a considerable overlap in size distribu- 

 tion. As a result, an aging error of 1 or 2 yr 

 may occur if a clam were assigned an age 

 based on size alone. Fraser and Smith (1928) 

 found a similar disparity in the range of sizes 

 within annular age groups for P. staminea 

 from British Columbia, and Quayle (1952) 

 reports that length-frequency distributions could 

 not be used to determine age groups for 

 Veiierupis pullastra in Scotland. 



Growth 



Our study indicates that P. staminea grows 

 much more slowly in Galena Bay, Prince 

 William Sound, than in British Columbia 

 (Fraser and Smith, 1928). The average length 

 for P. staminea at the end of its first year in 

 Galena Bay is approximately 2 mm (Table 2, 

 Figure 6) while in British Columbia it is ap- 

 proximately 12 mm (Table 3). Slow growth in 

 Alaskan waters is probably the result of severe 

 winter conditions which reduces clam-feeding 



activities at this time. The adverse effect of low- 

 water temperatures on growth rate has been 

 reported for a number of bivalve molluscs in- 

 cluding Pinctada martensii (Kobayashi and 

 Watabe, 1959), Crassostrea virgurica (Loosa- 

 noff, 1958), Mytilus edulis and Mercenaria 

 mercenaria (Pratt and Campbell, 1956). 



Both Fraser and Smith (1928) and Smith 

 (1928), working in Canadian waters, observed 

 that the most favorable growth occurred on 

 beaches near strong tidal currents while poor 

 growth took place on beaches at the heads of 

 quiet bays. An examination of older specimens 

 of P. staminea from Galena Bay supports this 

 observation (Feder, unpubl. data). The cumula- 

 tive growth curve (shell length) for littleneck 

 clams from Shell Beach is nearly a linear 

 expression (Figure 6). This beach, the most 

 exposed study site, is subject to strong tidal 

 currents (Table 1). On the other hand, cumula- 

 tive growth plots for Eater Beach and Indian 

 Creek Flat, protected locations with little cur- 

 rent or wave action, provide more standard 

 growth curves which become asymptotic at 

 about age 10 (Figure 6). 



Recruitment and Distribution 



The differences in year-class strength of 

 P. staminea noted in Galena Bay (Figures 7, 8) 

 have also been observed for other bivalve 

 species, e.g., Saxidomus giganteus (Fraser and 

 Smith, 1928), Cardium edule (Hancock, 1970), 

 and Venerupes pullastra (Quayle, 1952). There 

 are a number of interrelated factors affecting 

 larval production in bivalve molluscs, but in 

 general the most important ones appear to be 

 the number and physical condition of mature 

 females and the temperature requirements 

 necessary for the liberation of the larvae 

 (Hancock, 1970). Survival of larvae in the 

 plankton and successful settlement are also 

 affected by several environmental conditions, 

 especially temperature, adequate food supply, 

 predation, and favorable conditions for settle- 

 ment (Thorson, 1966, 1971; Christensen, 1970; 

 Hancock, 1970). Data on most of these condi- 

 tions are not available for P. staminea in 

 Prince William Sound. 



Hancock (1970) working in England noted 



674 



