The intertidal culture of clams is also carried out by farmers who 
own the beds or lease tidelands from the state. Most of the farms are 
small, not exceeding 50,000 pounds per year—with a total annual harvest 
of 2 to 3 million pounds. Individuals or families with beachfront 
property may supply commercial farms with clams on a part-time basis, 
especially in the summer. 
Puget Sound supports substantial subtidal clam fisheries. All 
harvesting operations occur on leased lands managed and controlled by the 
state. The geoduck clam fishery, which began in the 1970's, accounts for 
the majority of the present 5 million pound per year harvest. 
Finally, within the last 10 years, the raft culture of blue mussels 
( Myti1 us edul i s ) in subtidal and intertidal waters by farmers in central 
Puget Sound has begun to make a small but growing contribution to the 
state shellfish production. 
Types and Sources of Contamination 
Shellfish that strain the seawater for all or a portion of their 
food, such as clams, oysters, and mussels are very efficient feeders, and 
can readily remove from the water small particles, such as bacteria (or 
bacteria-laden silts). When bacteria, or particles containing toxic 
chemicals, are ingested by the shellfish, the edible shellfish meats 
become contaminated. Numerous areas throughout Puget Sound have been 
closed to commercial shellfishing (Table 1 and Figure 2), with the vast 
majority of these closures being related to bacterial contamination. 
Bacteria 
Water that has been polluted by human sewage is hazardous because 
several diseases are transmitted through human wastes, such as typhoid, 
cholera, dysentary and hepatitus. Usually, disease causing viruses are 
not measured directly in the water. Instead, the numbers of indicator 
bacteria, i.e., total coliform, fecal coliform, and fecal streptococci, 
are measured. These bacteria are known as indicator organisms because 
they are supposed to indicate the presence of sewage and ideally are 
correlated with the number of pathogens in a water sample. All 
commercial shellfish growning areas are monitored for these indicator 
organisms by the Washington Department of Social and Health Services 
(DSHS). 
50 
