clams at Pismo Beach developed into the ripe stage 1 month earlier than 

 intertidal or subtidal clams at Moss Landing. 



The partly spent stage (Fig. 14) is important because it indicated 

 onset of spawning and difficult to distinguish from the late active stage 

 because in both stages the gonad was not completely full of eggs. Clams 

 in the partly spent stage were found from May to December with the 

 greatest occurrence from June to September (Fig. 15). 



The spent stage of the clam was dominate from October to December 

 (Fig. 15) although some clams were found in this stage throughout the 

 year. The few ova remaining in some of the ovaries were usually 

 completely resorbed by April, with the exception of subtidal clams from 

 Moss Landing. In these clams the ova persisted longer and, in a few 

 cases, were found in clams that were in the early stage of gametogenesis . 



The inactive stage predominated from December to March but some 

 clams were in this stage from October to May (Fig. 16). 



b. Sex Ratio and Size at Maturity . Of the 289 clams examined, 142 

 were male, 144 were females (Fig. 17), and 3 were hermaphroditic. The 

 small clams (less than 44 millimeters) and the large clams (more than 



44 millimeters) have a sex ratio that is not significantly different from 

 1:1 (chi square, 0.50<P<0.30) suggesting that sex, once determined does 

 not change with age. 



Most clams reached sexual maturity at a length of 20 millimeters 

 (Fig. 17); however, one clam reached this maturity when 13 millimeters 

 long. 



c. Hermaphroditism . Although three hermaphrodite clams (Fig. 18) 

 were found during the study, an analysis of the rate of occurrence of 

 hermaphroditism was not made. A complete cross section of the foot 

 would have to be examined to adequately check for hermaphroditism since 

 usually only a few follicles are of the opposite sex (Coe, 1947). 



4. Discussion . 



The main spawning period of Pismo clams at Pismo Beach and Monterey 

 Bay occurred during September and October with some occurrences from June 

 to August. Similar results on Pismo clams at San Diego were obtained by 

 Coe (1947) . The results were in contrast to the late spring or summer 

 spawning common in the family Veneridae. Ansell (1961) reported that 

 spawning in the European clams, Venus orata and Venus aasi-na, occurred in 

 May, Venus fasaiata from February to July, and Venus striatuta in summer. 

 Mercenavia mevoenavi.a ^ the northern quahog, spawns in summer (Loosanoff , 

 1937; Porter, 1964), Venevupis japoniaa and Protothaaa staminia on the 

 coast of British Columbia, spawn in late spring (Quayle and Bourne, 1972), 

 the European Venus pultastva spawns in June (Quayle, 1952) , and Saxidomus 

 giganteus , smooth Washington clam species, spawns in April and May 

 (Fraser and Smith, 1928). 



35 



