Investigation of Pacific oyster mortalities was carried
out over a six-year period in major northern and central
California oyster rearing areas. Effort was directed toward
defining areas of high oyster mortality and determining
possible etiologies of observed losses through monthly monitoring and sampling of experimental and commercial oyster populations in Morro Bay, Elkhorn Slough, Drakes Estero, Tomales Bay and Humboldt Bay.
Hydrographic data was collected in all areas and a two year
study of phytoplankton and water quality in Humboldt Bay
was initiated to observe relationships with oyster mortality
patterns.
Research undertaken to develop methods to alleviate losses among Pacific oyster populations included an oyster seed source study, investigation of optimal oyster culturing
techniques and preliminary efforts to develop a mortality
resistant strain of oysters in Humboldt Bay. The cause of
mortality among Pacific oyster populations in Humboldt Bay
remains uncertain but a bacterial etiology correlated with
elevated water temperatures is suspected. The best method
of circumvention of losses appears to be the culturing of
"domestic" seed sources on racks. (55pp.
