PAUL and FEDER: LITTLENECK CLAM IN GALENA BAY 



Figure 3. — The use of shell sculpture as a means of 

 aging Protothaca staminea. Above: Photograph of a 

 5-yr-old P. staminea illustrating shell sculpture. Below: 

 Graphic illustration of the shell sculpture between two 

 annuli A = annulus (winter growth). B = radial sculp- 

 ture line. C = concentric growth line. A' = annulus. 

 A to C = increasing distances between concentric growth 

 lines C to A' = decreasing distances between concentric 

 growth lines during late summer and fall growth. 1, 2, 3, 4, 

 and 5 = successive annuli. Clam length = 1 1 mm. 



with an IBM 360 Computer. Several additional 

 programs were designed to arrange and plot 

 the data. A one-way analysis of variance was 

 used to test the accuracy of the annular aging 

 technique. 



RESULTS 



Aging 



Annuli on valves less than 20 mm in length 

 were quite distinct. False checks-* which super- 



"* False checks are series of concentric growth rings, 

 resembling annuli, formed in spring and summer when 

 growth is normally most active. These checks are also 

 termed disturbance checks. 



ficially resemble annuli (see first section under 

 Discussion for comments), although present, 

 could be readily distinguished from true annuli. 

 Although false checks and shell abrasion made 

 aging more difficult for clams greater than 

 20 mm in length, specimens from all three 

 study sites were aged. The oldest clam col- 

 lected in Galena Bay was 15 yr old with a 

 length of 47.6 mm. 



The validity of the annular aging method 

 was examined with a standard one-way analysis 

 of variance, utilizing the individual shell heights 

 within each age class from Shell Beach as a 

 basis for comparison (Snedecor, 1956). The 

 calculated F ratio indicates that, in general, 

 age classes, as defined by shell heights, are 

 statistically distinguishable (P = 0.01; N — 

 368). Similar data plotted for Eater Beach 

 further indicate the integrity of the aging 

 method used (Figure 4). In addition, annuli 

 for 3 yr of growth have been validated by the 

 recovery and subsequent examination of over 

 100 marked P. staminea from Galena Bay 

 (Feder and Paul, unpubl. data). 



Histograms plotting size and age indicate 

 that age classes form fairly distinct but over- 

 lapping groups (Figure 5). 



8 10 12 



Length (mm) 



14 



16 



la 



Figure 4. — Average length and height plotted as a func- 

 tion of age for specimens collected on the Eater Beach 

 transect. Galena Bay. Each point represents a mean 

 value for specimens of a given age group collected at a 

 single station. 



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