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 possessed. Undersized Pismo clams must immediately be reburied in the area where dug. Bag limit is 10 Pismo clams. Hours of clamming are 1/2 hour before sunrise to 1/2 hour after sunset.