Creature Feature: Gaper Clams

gaperclamBoth the Pacific gaper clam and the fat gaper clam may be found on California beaches statewide. They prefer fine sand or firm, sandy-mud bottoms, especially in bays, estuaries, and more sheltered outer coastal areas.  Humboldt Bay, Bodega Bay, Tomales Bay, Drakes Estero, Elkhorn Slough, and Morro Bay are popular digging areas.

  • Distinguishing Characteristics
    Largest clam in California.
  • Relatively thin, whitish shells with thick brown varnish-like coating that is often eroded. May be stained black in mud habitat.
  • Black siphon extremely long, with a pair of flaps at the end.
  • Siphon cannot be withdrawn into shell.

Life History & Other Notes
Gaper clams feed on plankton and bits of food they filter from the water. In intertidal clam beds, feeding occurs during the high tide period.

In central California reproduction occurs year-round. The young swim freely until they settle onto the sea floor, after which they move downward into the sediments. Gaper clams grow about one inch per year for the first four years, after which the growth rate begins to slow.

Clammers generally use shovels to dig for these clams, which may be found as deep as four feet in sand or mud. In muddy areas, three-foot lengths of PVC pipe about 12 to 15 inches in diameter are often used to prevent holes from caving in. Gaper clams are generally used in clam chowder or fried and served as a main dish.

 Gaper Clams Quick Facts

Scientific Names

Pacific gaper clam – Tresus nuttallii

Fat gaper clam – Tresus capax

Other Common Names: horseneck clam, horse clam

Range & Habitat : Statewide in sand or firm, sandy-mud bottoms

Length & Weight: To 10 in. and 5 lb.

Life Span: To 17 years

Diet: Feed on suspended plankton and detritus

Excerpt from the California Finfish and Shellfish Identification Book. Single copies of the book are available to California residents free of charge by emailing a request to

For complete clamming regulations, see the current Ocean Sport Fishing regulations booklet.

The California Department of Public Health coordinates a routine monitoring program along the California coast to sample mussels and other shellfish like clams and scallops for the presence of Paralytic Shellfish Poisoning (PSP) and domoic acid toxins. If toxin levels are high enough, warnings and quarantines are issued to protect the recreational fishing public and shellfish consumers. The California Department of Fish and Wildlife posts these warnings and quarantine notices on the Marine Region website. It is a good idea to check the California Department of Public Health’s Shellfish Biotoxin Information Line at (510) 412-4643 or toll-free at (800) 553-4133 before going clamming.