EFFECTS OF ENGINEERING ACTIVITIES ON 

 THE ECOLOGY OF PISMO CLAMS 



by 

 James Nybakken and Mark Stephenson 



I. INTRODUCTION 



The Pismo clam (Tivela stuttoruni) is an important sports and 

 commercial bivalve mo Husk inhabiting open sand beaches from Half Moon 

 Bay, California, to Socorro Island, Mexico (Herrington, 1930) . This 

 study covers the gonad and spawning cycle, distribution, and reproduction 

 cycle of the Pismo clam, summarizing the results obtained during a 2-year 

 study from January 1972 to January 1974. However, because of vandalism 

 and weather, the growth shelter section is incomplete. 



II. DISTRIBUTION 



1. Introduction. 



Before this study, information on the qualitative and quantitative 

 distribution of Pismo clams in Monterey Bay was limited. The California 

 Department of Fish and Game provided an aerial survey of Monterey Bay 

 conducted during low tide on 15 January 1969. At that time 87 clammers 

 were found between the Salinas River mouth and Elkhorn Slough, 57 between 

 Elkhorn Slough and the Pajaro River, 156 between the Pajaro River and 

 Monterey Bay Academy, and 62 between Monterey Bay Academy and Rio del Mar 

 (Dahlstrom, 1973, personal communication) . Assuming that clammers are 

 found where clams are, a rough estimate was made on the location of clams 

 in Monterey Bay. 



The only quantitative data available were obtained by the California 

 Department of Fish and Game in 1968. Transects were used to acquire the 

 data by digging a 6-inch-wide by 6-inch-deep trench from high tide level 

 down to low tide level. Six clams at Sunset State Beach, four clams about 

 1 mile and six clams about 1.5 miles south of Sunset State Beach, and 

 three clams at Zmudowski State Beach (Dahlstrom, 1973, personal communica- 

 tion) were obtained from these transects. However, the transects were 

 of limited value for estimating the density and dispersion patterns due 

 to the small area surveyed and the lack of replicates. It was necessary 

 to devise a new system to adequately sample the clam population so these 

 estimates could be made. Since the California Department of Fish and 

 Game surveys covered only a few areas, it was also necessary to sample 

 representative sites for clams around the bay. 



Although there were rumors of extensive subtidal populations of 

 Pismo clams in various localities in Monterey Bay, these beds were not 

 documented. Determination of the beds is important for protection from 

 exploitation or damage from dredging or dredged material if the 



