Feasibility of suspension culture of oysters at an offshore site on the Texas coast
The feasibility of off-bottom oyster culture at a petroleum platform offshore from High Island, Texas was investigated. Oysters were dredged from a natural reef in upper Galveston Bay at a spoil area adjacent to the Houston Ship Channel at Morgan Point. Experimental and control oysters were suspended in plastic mesh Vexar bags. Control oysters were held in the estuary at two levels in the Galveston Ship Channel at Pelican Island, Galveston. Experimental oysters were held at five levels in an initial (20-month) experiment and at two levels in a second (12-month) experiment. In the initial (20-month) experiment all control oysters were lost to vandalism. During the initial, 20-month study, the growth and condition of offshore oysters was similar at the five levels. Oysters had growth rate of 1.2 to 1.4 mm per month representing an increase in length of 94% to 150%. Oysters increased in weight 80 to 130g representing an increase of 94% to 150% for the 20 months. The condition was best in June 1973 after 5 months placement offshore (condition index of 14.8, 15.5, 14.7, 13.5 and 13.2 for levels 1-5, respectively). The condition was lowest in June 1974 (2.2, 2.1, 1.3, 1.4 and 1.5 for level 1-5, respectively). Offshore ninety oysters were lost due to mortality during the initial (20-month) experiment. Sixty-three percent were from the upper two levels. One hundred forty-five oysters were lost through disappearance (ie., bag failure, theft, etc.). Fifty-eight percent were from the bottom two levels. Most oyster disappeared in February 1974 (47% of all disappearances). During the second (12-month) experiment, change in length was not significantly different between stations, but change in weight was significantly greater at the estuarine control station (645 g vs 464 g). The lower level, for both sites, showed significantly greater increase in length (202 mm vs 144 mm). The average weight increase was greater at the upper level offshore and at the lower level at the estuarine station. The condition was better for oysters at the estuarine station. The chlorophyll a at the estuarine station was twice that offshore, indicating a larger estuarine phytoplankton population. However, the generic composition of the phytoplankton was similar at both stations. More oysters died offshore (50) than at the estuarine station (32) during the 12-month experiment; this was possibly related to the greater incidence of the fungus Labyrinthomyxa marina in oysters offshore. This study should be considered as preliminary due to the small sample size and should be repeated utilizing a larger number of oysters.