in 1973 probably comprised the 40- to 70-millimeter-size classes. Most 

 o£ these clams were probably spawned during the summer of 1970. The 

 number of juvenile clams 10 to 35 millimeters long on these two beaches 

 was significantly less in 1973 than 1972, suggesting a poor year for 

 survival (Mann-Whitney U test (see App.), P = <0.05). 



In testing the vertical distribution of clams, seven intertidal 

 heights ranging from the -0.2- to 3.4-foot tidal level were sampled at 

 Monterey Bay Academy to determine if clams were more abundant at different 

 tide levels. The results (Fig. 3) showed no clams above the 2.6-foot 

 level. Densities of clams from levels -0.2 to 2.6 feet were tested for 

 significant differences with the Student -Newman- Keuls multiple range 

 test (Woolf, 1968). There was no significant deviation in densities 

 among levels which indicated very little change in densities within the 

 vertical range. 



Results of the spatial dispersion studies are given in Table 3. All 

 clams less than 39 millimeters long and most clams more than 39 milli- 

 meters long were randomly dispersed except for an apparently contagious 

 dispersion of clams from Rio del Mar in 1972 and Monterey Bay Academy in 

 1973, and a regular dispersion of clams from Moss Landing in 1972. The 

 test used in the analysis of the variance-mean ratio is only used 

 effectively as a comparative index' of dispersion when the means and 

 number of clams for each sample are similar (Elliott, 1971J. Since the 

 means and number of clams were not similar in this test, comparisons 

 could not be made among the various beaches; the degree of clumping in 

 the samples which showed contagious dispersion patterns could not be 

 determined. Most of the clams were randomly dispersed, and in a few 

 instances where this was not the case, additional data to test the 

 significance or degree of departure from randomness were not available. 



4. Discussion . 



During the study period, Pismo clams in Monterey Bay occurred between 

 the Salinas River and Rio del Mar with the heaviest concentrations at 

 Sunset State Beach and Monterey Bay Academy. No clams were found south 

 of the Salinas River, and only one clam was found at Santa Cruz. The 

 aerial survey of Monterey Bay conducted in 1969, by the California 

 Department of Fish and Game (Dahlstrom, 1973, personal communicationj 

 showed a similar distribution of clammers. Most of the clammers were 

 concentrated near beaches where the highest densities of clams were 

 recorded during the study period. No clammers were found at Santa Cruz 

 or south of the Salinas River. 



Surprisingly, the density of large Pismo clams south of Monterey Bay 

 at Pismo Beach, known among sports fishermen for its large clam popula- 

 tion, was significantly lower than at Sunset State Beach and Monterey 

 Bay Academy. During the years of commercial clamming, more than 10 times 

 as many Pismo clams were harvested at Pismo Beach as in Monterey Bay 

 (Herrington, 1930) . The reason for the lower density of Pismo Beach is 



15 



