Pismo clam populations fluctuate dramatically due to a variety of natural influences. A fragile and valuable resource, Pismo clams may be taken under the following regulations: Clammers must have a fishing license and an accurate (rigid) measuring device in possession. Only Pismo clams at least 4.5" in length may be possesses. Undersized Pismo clams must be immediately reburied in the area where dug. Big limit is 10 Pismo clams. Hours of clamming are 1/2 hour before sunrise to 1/2 hour after sunset.