not known, but it is believed to be the result of heavy fishing. It 

 is also possible enough samples were not taken to adequately estimate 

 the density. Although density is lower at Pismo Beach, the number of 

 clams available to clan„ners may be greater due to a larger surface 

 exposure during low tides. This area is a result of a flatter beach 

 slope at Pismo Beach in comparison to the beaches of Monterey Bay. 



Large populations of subtidal Pismo clams were not found in Monterey 

 Bay as reported by Fitch (1965) at Zuma Beach in southern California. 

 The highest density, 0.4 clams per square meter, was found at Moss Landing 

 which is considerably lower than the six clams per square meter found by 

 Fitch (1965) at Zuma Beach. Diving observations during the clam 

 collection for the reproductive study suggested the density at Moss 

 Landing may have been higher than 0.4 clams per square meter. As many 

 as six clams were frequently collected from an area of approximately 

 1 square meter. Large numbers of subtidal clams were also found at 

 Pismo Beach where 20 clams were collected on one occasion out of an area 

 estimated to be smaller than 2 square meters. 



Densities of Pismo clams did not deviate significantly at seven 

 different intertidal heights; however, the different levels were only 

 sampled on one beach. Weymouth (1923) and Baxter (1961) reported that 

 1-year-old Pismo clams were mainly found in the middle part of the 

 intertidal range; the tide level at the middle part of the tidal range 

 was not reported. During this survey, very few clams of that age (10 to 

 39 millimeters long) were found at any tide level (Fig. 3). But this 

 could be an artifact of sampling only one beach. No clams were found 

 above the 2. 6- foot tidal level in Monterey Bay. 



In most areas surveyed Pismo clams were randomly dispersed. This 

 type of dispersion has also been found in other bivalves, i.e., 

 Sarobicularia plana (Hughes, 1970), Mulina lateralis (Jackson, 1968), 

 Gemma gemma (Jackson, 1968), Cardium edule (Kosler, 1968), and Maooma 

 baltioa (Kosler, 1968). Large Pismo clams and other bivalves regularly 

 dispersed have been reported in other studies. Tellina tenuis, for 

 example, is regularly dispersed in low densities and randomly dispersed 

 in high densities (Holme, 1950); Mya arenavia shows a clumped dispersion 

 pattern (Gaucher, 1965) . 



5. Conclusions. 



The highest intertidal densities of Pismo clams in Monterey Bay were 

 found at Monterey Bay Academy and Sunset State Beach. Densities 

 decreased to the north and to the south of these beaches. No clams were 

 found south of the Salinas River; only one juvenile clam was found at 

 Santa Cruz at the north end of the bay. The density of large clams 

 south of the bay at Pismo Beach was significantly less than densities at 

 Monterey Bay Academy or Sunset State Beach. The mean densities of Pismo 

 clams at seven intertidal heights did not differ significantly indicating 

 there was no vertical preference. In most of the surveys the clams were 



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