Moss Landing. Observations of sea otters feeding on Pismo clams and the 

 increase of broken clamshells on the beach strongly suggest the sea 

 otters are the principal cause of the decline. 



Fortunately, there are still small clams at Moss Landing. In the 

 past there have been enough clams for Moss Landing to be the mainstay 

 of a commercial fishery for Pismo clams in Monterey Bay [Herrington, 

 1930). Whether the population will return to prior levels will depend 

 upon the satisfactory recruitment in future years from clam populations 

 not depleted by the sea otters. 



Although the density of Pismo clams has declined at Moss Landing, 

 the lowered density may be the more natural density. Before man exter- 

 minated the sea otter from Monterey Bay and the early commercial fishing 

 began, the otters may have fed upon Pismo clams with regularity, keeping 

 the density at a lower level. 



5. Conclusion . 



During the spring and summer of 1973 sea otters feeding on Pismo clams 

 were observed at Moss Landing, California. Densities of Pismo clams 

 before the sea otter's arrival at Moss Landing and after their departure, 

 catch-per-unit effort data in the collections of clams for reproduction 

 study, and clammer interview data all indicate a decrease in the density 

 of large Pismo clams at Moss Landing. Direct observations of the sea 

 otters feeding on Pismo clams and the increase in broken clamshells on 

 the beach suggest that sea otters were the principal cause of the decrease. 



V. REPRODUCTIVE CYCLE 



1 . Introduction . 



Previous studies on the reproduction of Pismo clams covered southern 

 California and several locations in Baja, California (Mexico] (Coe, 1947; 

 Coe and Fitch, 1950). These studies suggest the reproductive cycle in 

 Pismo clams is extended in the southern part of its range and somewhat 

 restricted in the northern part. A restricted spawning season in the 

 northern part of an animal's range, which is not uncommon in many inter- 

 tidal animals (Giese, 1959), has also been found in the bivalves Mya 

 avenaria (Ropes and Stickney, 1965) and Meroenaria mercenaria (Porter, 

 1964). Since Monterey Bay is near the northern limit of the Pismo clam's 

 range, there was concern that spawning would only occur during the 

 warmest years or would not occur at all and the clams would depend on the 

 recruitment of larvae from more southerly populations. Previous informa- 

 tion concerning the reproductive cycle in Monterey Bay (Giese, et al., 

 1967) showed the weight of the gonad increased during the spring, reached 

 a maximum from June to September, and then rapidly decreased. No 

 evidence was presented to show whether the clams spawned their gametes or 

 resorbed them. The spawning of subtidal populations of clams which were 

 found in large numbers at Zuma Beach (Fitch, 1965), Pismo Beach, and 



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