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Abstract

Pismo clams, Tivela stultorum, were observed at Rincon Beach, CA to find patterns of abundance and size distribution along a depth gradient from the intertidal, where recreational clammers have access on foot, to the subtidal, where clammers only have access with more specialized snorkeling or SCUBA equipment. Size and abundance patterns were compared between the intertidal and subtidal regions. A heuristic model was created to predict the effects of predation and wave action on clam density. Clam abundance was significantly greater in the intertidal than the subtidal and displayed a Gaussian distribution across the entire distance sampled. While Pismo clam abundance was greater in the intertidal region, the mean clam size was significantly greater in the subtidal region. Moreover there was no difference in the distribution of sublegal clams between regions. However, there were significantly more legal sized clams in the subtidal than the intertidal. Our results suggest that recreational fishing pressure and exposure to the wash zone, in addition to other factors, influence the distribution of clams at Rincon Beach, CA. Further elucidating the patterns and mechanisms contributing to the distribution trends of the Pismo clam could aid in overall population estimates and the future management of the Pismo clam fishery.

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