| Summary: | Investigation of Pacific oyster mortalities was carriedout over a six-year period in major northern and centralCalifornia oyster rearing areas. Effort was directed towarddefining areas of high oyster mortality and determiningpossible 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 yearstudy of phytoplankton and water quality in Humboldt Baywas initiated to observe relationships with oyster mortalitypatterns.Research undertaken to develop methods to alleviate losses among Pacific oyster populations included an oyster seed source study, investigation of optimal oyster culturingtechniques and preliminary efforts to develop a mortalityresistant strain of oysters in Humboldt Bay. The cause ofmortality among Pacific oyster populations in Humboldt Bayremains uncertain but a bacterial etiology correlated withelevated water temperatures is suspected. The best methodof circumvention of losses appears to be the culturing of"domestic" seed sources on racks. (55pp.)
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