UC San Diego Library – Scripps Digital Collection

Commercially the Pismo clam (Tivela stultorum)ranks first in importance in California among the clams and third among all the mollusks, being exceeded only by the oyster and the abalone. A second reason for considering this species is that there has been such evidence of depletion as to lead to increasingly more stringent protective laws, all of which have been urged by the residents of the county in which the clam is most abundant. In 1911 the legal size, below which no clam might be taken, was fixed at 13 inches in circumference and the bag. limit, or maximum number permitted to one person, at 200 per day. In 1915 the legal size was reduced to 12 inches in circumference and the bag limit to 50. In 1917 the legal size was changed to 4¾ inches in greatest length (a slight reduction). In 1919 the bag limit was further reduced to 36 per day. In 1921 the bag limit became 15. An accurate study of the cause and extent of this apparent diminution must await knowledge of at least the fundamental facts of the life history of this clam. This lack the present study attempts to supply. The more important features are considered to be: the habits, enemies and mortality of the adult; the rate of growth and the factors affecting it; the age at certain significant periods, particularly at sexual maturity and at the time when the legal size is reached; the most common age of clams forming the commercial catch; the season of spawning and the productivity; and the habits, enemies and mortality of the young. Some answer to each of these questions will be attempted.