available energy, indicating the kinetic energy (velocity) of the 

 depositing agent [i.e., waves) (Sahu, 1964). Beaches with a steep slope 

 and large mean grain size represent a high energy beach; beaches with a 

 gentle slope and smaller mean grain size represent a low energy beach. 

 Therefore, the beaches without clams may be characterized as high energy 

 beaches, and beaches with clams as low energy beaches. This does not 

 imply a cause and effect relationship because additional parameters 

 affect Pismo clam distributions. 



There was no significant difference in sorting coefficients between 

 beaches with clams (0.55 ±0.34) and beaches without clams (0.50 ±0.28). 

 The value of sediments ranged from well sorted to moderately sorted 

 according to a verbal scale of sorting by Folk (1966). The higher the 

 sorting coefficient, the poorer the sediment is sorted. Interestingly, 

 there was significant correlation between the sorting coefficients and 

 number of clams, with a higher number of clams associated with a higher 

 sorting coefficient (Table 4) . The highest correlation was found in the 

 greater than 39-millimeter class range, which represented the first-year 

 class of Pismo clams. 



5. Conclusions . 



There are correlations between grain size and slope of beaches with 

 and without Pismo clams in Monterey Bay. Beaches with clams have a 

 smaller grain size and beaches without clams have steeper slopes. 



IV. SEA OTTER PREDATION ON PISMO CLAMS 



1. Introduction . 



Sea otters (Enhydra Zutris) were rarely observed in the Moss Landing 

 area before the spring of 1973. After the arrival of a substantial 

 number of otters during the spring and summer of 1973, broken Pismo 

 clamshells were found on the surface of the sand in both intertidal and 

 subtidal zones. Since Pismo clamshells are thick and resistant to 

 breakage by the surf, the increase in the number of broken clamshells was 

 probably due to the sea otters. The following September, a feeding rate 

 was taken for the sea otters observed feeding on Pismo clams at Moss 

 Landing. Densities of Pismo clams in this area were obtained during the 

 presence of the sea otters and after departure the following fall. The 

 effect of sea otters on the clam population was then estimated by 

 comparing these densities with the estimates of clam density taken in 

 1972. 



2. Methods and Materials . 



The density of Pismo clams was determined by methods described in the 

 preceding section. Observations of the sea otters feeding on Pismo clams 

 were made during September 1973, using a Bausch and Lomb 15-60X zoom 

 telescope. During each observation, the time and location of feeding, 

 estimated size of clam, and prey item were recorded. 



24 



