Geoduck Clam    Panopea abrupta (generosa)

Would you believe that the geoduck clam which has a maximum weight of 20 pounds and in 9 inches across the shell is not the world’s largest clam?  It’s true.  The largest clam is the south pacific giant clam called Tridacna.  It can grow to 4 ft and weigh more than 500 pounds.  But for our part of the Pacific Ocean, the geoduck is the largest.

The animal is so large that it cannot retract the siphon into it’s shell.  The siphon of a large geoduck clam can be some 3 ft in length when extended.  By the way the siphon of a clam is the way they view the world.  Whether it’s short (cockle) or long (geoduck) it acts as a two way super highway.  One section of the siphon handles water coming into the clam from which it gains oxygen and food as it passes through the gills.  Waste water is then sent out the other section.  Another part of the of clam anatomy that is often seen is the foot.  It is used for digging.  The geoduck foot is rather small as they are not fast diggers, only digging deeper as they grow bigger.  Some clams such as cockles have a huge foot that not only allows fast digging but can be use to flip the clam to escape predators.

Research by the Washington Department of Fish and Wildlife in the 1980’s showed that the average geoduck age was around 70 years old with some as old as 160 years.  Once the clam grows large enough the dig below the top several inches of sediment few predators could attack it successfully.  The one shown in the photograph is about 2 ft long.

The clam is very popular in several asian countries leading to high prices for clams commercially harvested in Washington.  Currently most of the attention is directed at culture of geoducks in the intertidal zone.  This has generated considerable controversy about the environmental impact of such operations.  Contact the Department of Fish and Wildlife and the Department of Natural Resources for more information.