Geoduck and Horseclam biology

Geoducks and horse clams are bivalves characterized by hinged shells.  Bivalves include commercially important clams, oysters, mussels and scallops.  Geoducks are among the oldest living animals in the world. The age of many clams can be estimated by the growth rings or annuli on the shell, similar to the rings of a tree trunk.  From 1993 to 2006 UHA and DFO researchers have collected about 26,000 geoducks from surveys conducted throughout the B.C. coast.  This research has uncovered the oldest geoduck aged to date in the world, a 168 year old geoduck from Tasu Sound on the west coast of the Queen Charlotte Islands.   Horse clams reach estimated ages of 20 years or more.  

Geoducks and horse clams are among the largest bivalves as well.  The geoduck is the largest intertidal clam in the world with an average weight of approximately 1 kg (2.2 lbs) in B.C. and a shell length to 195 mm (7 ¾").  Huge geoducks have been recorded weighing up to 4.5 kg (10 lbs) with larger denizens of the deep reported by fishermen in the field.

There is one species of geoduck in B.C., Panopea abrupta and two species of horse clams, the pacific gaper, Tresus nuttallii, and the fat gaper, T. capax.  Divers identify these three species underwater by their "shows" (visible exposed tip of a siphon or dimple left in the sand from a retracted siphon).  Commercial geoduck harvesters are expert "show readers" in high visibility conditions and zero visibility conditions where they feel for shows.
There are commercial fisheries for geoducks in B.C., Washington and Southeast Alaska.  There is also a growing aquaculture industry for geoducks in Washington and B.C.  
There are a number of other Panopea clam species throughout the world.  Panopea japonica in Japan and Korea,  Ponopea zelandica and P. smitha in New Zealand, Panopea abbreviate from the southern part of South America (Argentina and Chile), and Panopea globosa in Mexico.  Detailed biological information available is Panopea zelandica, the New Zealand geoduck clam.  P. zelandica is smaller than the Pacific geoduck, weighing up to 1.3 lbs and reported in lower densities than abrupta.  

There appears to be two Panopea species being harvested in Baja Mexico, Panopea globosa mostly from the Gulf side of the Baja (limited numbers from the Pacific side) and Panopea abrupta only from the Pacific side.  The discovery of potential commercial quantities of Panopea abrupta on the Pacific side represents a significant range extension for this species.

 To learn more about where geoducks live, what they eat and what they do for sex go to DFO's Fish Stocks of the Pacific Coast: Online Book at: http://www-comm.pac.dfo-mpo.gc.ca/publications/speciesbook/invertebrates/geoduck.html