Summary of Oyster Studies Along the Texas Coast - Survey of Oyster Populations and Associated Organisms

Both seed oyster Crassostrea virginica stock and market oyster stock continued to decline in Aransas, San Antonio, Matagorda, and Galveston Bays. Losses appeared to be most severe in the Aransas Bay area, diminishing up the coast to Galveston Bay. Much of the loss in the middle coast was attributed to Aransas Bay disease which affected young seed oysters as well as the older market oysters. The disease was found in 1963 in Aransas Bay and was apparently associated with the moralities in San Antonio and Lavaca Bays. During 1964 the disease spread into Copano Bay, most of San Antonio Bay, Lavaca Bay, and Matagorda Bay. The organism responsible for Aransas Bay disease was identified by Dr. J.G. Mackin as an intre-cell organism similar to that associated with Malpeque Bay disease in Canadian waters. Sever moralities in Tres Palacios Bay appeared to be caused by Dermocystidium marinum judging by the high infection incidence found in samples during the late summer. However, the catastrophic losses among seed oysters was more characteristic of Aransas Bay disease. In Galveston Bay Dermocstidium spread further up the bay than in 1963 and was assumed to be the primary cause of oyster moralities. Tray studies at two stations showed an annual mortality rate of approximately 50 percent, both in 1963 and 1964. Most of the mortality at each station was due to Dermocystidium. Oyster production, in spite of high moralities, set a new record during the 1964-65 season. Most of the harvest came from Galveston Bay where heavy fishing pressure compensated for the relatively low abundance of market oysters