station. Sample locations were selected at random with the diver 

 sampling a square-meter area, moving about 10 to 15 feet away for the 

 next sample. The divers introduced little bias in the selection of 

 sample sites because visibility was usually limited to 5 feet or less, 

 the bottom was homogenous, and clam siphons were not visible. The 

 sample was collected in the mesh bag, brought to the boat, and examined 

 for clams. The clams were then measured and returned. The remainder 

 of the sample was put into jars and preserved in 10 percent Formalin 

 solution. 



The spatial dispersion of Pismo clams at each of the locations was 

 determined by a chi-square test of the variance to mean ratio (see App.) 

 (Elliott, 1971). Small (less than 39 millimeters) and large (greater 

 than 39 millimeters) clams were separated by length for comparison and 

 testing dispersion because of different sized sampling units. 



3. Results . 



The intertidal and subtidal population densities, mean densities, 

 and 95 percent confidence limits (C.L.) are given in Table 1. The mean 

 densities at each location were tested between 1972 and 1973 for signifi- 

 cant deviation by one-way analysis of variance (Woolf , 1968) . No 

 significant differences in mean density were found at any of the locations; 

 however, in all cases subtidal densities were lower than intertidal 

 densities. Moss Landing had the largest subtidal population with a 

 density of 0.4 clams per square meter. The greater intertidal densities 

 were at Monterey Bay Academy and Sunset State Beach. Densities decreased 

 north and south of these beaches. A single juvenile clam was found at 

 Santa Cruz; no clams were found south of the Salinas River which includes 

 Marina Beach and the beaches at Fort Ord and Monterey. The densities at 

 the different locations were tested for significant deviations by using 

 a Student-Newman-Keuls multiple range test (see App.) (Woolf, 1968). 

 The results are given in Table 2. Density of small and large clams was 

 greater at Monterey Bay Academy in both years. Density of small and 

 large clams at Sunset State Beach in 1972 and 1973 was next highest. 

 Clams were also surveyed on 13 December 1973, at Pismo Beach, California, 

 for comparison with densities in Monterey Bay. The mean density of large 

 clams at Pismo Beach was 0.7 clams per square meter (95 percent C.L. ± 

 0.46). This was similar to the 1973 densities at Rio del Mar, Moss 

 Landing, or Zmudowski State Beach (Probability, P = less than 0.01), but 

 significantly less than the densities at Sunset State Beach and Monterey 

 Bay Academy. The mean density of small clams at Pismo Beach was one 

 clam per square meter (95 percent C.L.), which was similar to the 1973 

 densities at Monterey Bay Academy or Zmudowski State Beach (P = less than 

 0.01), but significantly higher than the densities at Moss Landing, 

 Sunset State Beach, and Rio del Mar. 



The size- frequency structure of the clam population is given in 

 Figure 2. Small clams 10 to 35 millimeters long were abundant only at 

 Monterey Bay Academy and Sunset State Beach in the summer of 1972, and 



10 



