Mortality and condition of the American oyster in Galveston Bay, Texas.




Soniat, T.M.
Smith, L.E.
Brody, M.S.

Journal Title

Journal ISSN

Volume Title



Mortality and condition of the American oyster, Crassostrea virginica, were studied on sixteen 0.1-hectare sites on reefs in Galveston Bay, Texas. Oyster mortality was evaluated by three methods- the box-count method (number of articulated empty shells/number of articulated empty shells plus live oysters), the catch-curve method (log frequency versus size), and by tray experiments in which open tray, closed tray, and predator- inclusion trays in which an oyster drill, Thais haemostoma was enclosed in each) were used. Estimates of average annual mortality based on the catch-curve method (0.76) and open-tray analyses (0.61) were similar but these methods contrasted with box counts. Mortality determined by the catch-curve method did not correlate significantly with oyster density; however, mortality was high and density values were low at the extremes of oyster distribution. A weight/volume condition index was positively correlated with salinity whereas intensity (i.e., weighted incidence, WI) of infection by Perkinsus marinus was positively correlated with salinity. The glycogen values of oysters from reefs with greater than a light infection level (WI> 2.00; n= 7) showed a significant negative correlation with WI. High mortalities were apparently the result of frequent flooding at low salinity sites, but appeared to be caused by the oyster drill and disease (due to the protozoan P. marinus) at high- salinity sites. Percentage of boxes is likely related to short- term mortality, whereas mortality estimated by the catch curve method is a measure of longer term mortality. Percentage of boxes was highest at the highest salinity sites where disease was most prevalent. Glycogen concentrations decreased as salinity increased, which may be related to more favorable conditions in fresher waters and/or higher levels of disease in saltier water.


p. 77-94.


American oyster, oysters, oyster fisheries, Crassostrea virginica, body conditions, mortality