Reproduction, body condition, age, and growth of a large sandy intertidal bivalve, Tivela stultorum

Abstract

The iconic Pismo clam Tivela stultorum (Mawe, 1823) once supported a thriving commercial and recreational fishery in California, but populations have declined statewide in recent decades, in part due to overfishing. To manage and restore populations, fishery managers need accurate life history information, but critical data on reproductive cycles, maturity, and growth rates is either unknown or many decades old. This project aimed to (1) determine annual reproductive cycles and body condition of Pismo clams; (2) identify environmental drivers of reproduction and body condition; (3) determine size-age relationships among clams in California; and (4) estimate growth rates. Up to 70 clams mo-1 were collected from Pismo Beach, CA, for histological analysis to determine reproductive stage, measure a body condition index, and estimate ages from shells. Additional clams and shells were collected from sites north and south of Point Conception to compare growth and age at legal size between these 2 major oceanographic zones. Data suggests that reproductive timing deviates only slightly from historical records, with clams spawning later in the year than decades ago. Body condition indices correlate with reproductive stage 3 Ripe, providing an inexpensive proxy to monitor Pismo clam reproduction. Growth was faster in warmer Southern California compared to Central California, but still substantially slower than historical estimates; we estimate that Pismo clams reach the current legal size (114 mm) in 11.1 yr, several years later than previous estimates. Collectively, these data are critical to improve and guide management decisions for this once-abundant species.