Tivela stultorum, (Mawe, 1823)
Tivela stultorum, also known as the Pismo clam, is a species of large, edible, saltwater clam, a marine bivalve mollusk in the family Veneridae, the Venus clams. This species is native to the eastern Pacific Ocean. As the name implies, the Pismo clam lives in Pismo Beach, California. It has been found at least as far south as 300 miles (480 km) south of the US–Mexico border in Baja California on the Pacific Ocean side, where strong surf sometimes washes ashore live clams. The indigenous peoples of California used this species for food.
The clam has two thick shells that share a large, symmetric triangular structure. A prominent hinge ligament connects the two shells. Its coloration varies from pale tan to dark brown, and some specimens have chocolate brown rays that start from the umbo. Shells can measure up to about 7.25 in (18.4 cm) in length.
Pismo clams typically inhabit exposed, sandy shorelines and can also occur near the entrances of bays, sloughs, and estuaries. They generally remain within the top 6 inches (15 cm) of sand. Although usually found in intertidal zones (most notably around Pismo Beach, Morro Bay, and Monterey Bay), they have been found to extend into deeper waters of up to 80 feet (24 m). In Southern California waters, larger clams predominantly reside at depths exceeding 20 feet (6.1 m).
Geographically, the species is found along the coast starting from central California and extending south into Magdalena Bay, Baja California Sur. Reported range limits vary by source: Fitch (1952) identifies Half Moon Bay as the northern limit, whereas Coan et al. (2000) document occurrences as far north as Stinson Beach.
This species is a filter feeder. Pismo clams are consumed by numerous animals, including marine and terrestrial predators such as crabs, sharks, humans, and sea otters. In the past, local clam declines along the California coast were attributed in part to sea otters, but a statewide intertidal survey in 2018 and 2019 did not find otter presence to be a predictor of clam presence at a regional scale.
The sexes are separate and occur in approximately equal numbers. Pismo clams can begin reproducing within their first year of life, well before reaching the legal harvest size. Individuals may live for several decades.
Pismo clams have long served as a food resource for Indigenous coastal communities in California, including the Chumash, who have harvested this species along the California coast for thousands of years. Between 1916 and its closure in 1947, California’s commercial fishery harvested a total of roughly 6.25 million pounds of the species. The Pismo clam was also subject to a recreational fishery, which continued until well into the 1980s. Pismo clam populations experienced substantial declines after historically intensive harvesting. Researchers have tried to explain these declines through excessive harvesting and unsuccessful recruitment.
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