An assessment of oyster dredge and patent tong sampling across varying reef structure
Margaret Wheat-Walsh, Zachary Olsen, Jennifer Beseres Pollack, Evan Pettis, Jake HarrisAbstract
Objective
The Texas Parks and Wildlife Department currently uses dredge sampling to monitor eastern oyster Crassostrea virginica reefs. However, dredges have been shown to produce biased sampling data with regard to the density and relative sizes of the oysters collected. The objective of this study was to compare the sampling performance of oyster dredges in reference to hydraulic patent oyster tongs.
Methods
Six reefs within the Mission-Aransas Estuary were sampled during this study. At each site, the density (n/m2) and size (shell height; mm) estimate of several oyster reef components (live oysters, articulated shells of dead oysters [boxes], and brown and black disarticulated oyster shells) were enumerated. In conjunction with the tong and dredge samples, each sample area was assessed with acoustic mapping procedures to better determine the reef structure and landscape.
Results
Results indicate that dredges show a size bias toward larger reef components. In addition, the comparability of dredge and tong density estimates varies with the landscape-scale patchiness of reef. Reef components with higher densities and more consistent distribution show greater disparity between dredge and tong density estimates (specifically, greater tong density estimates). This study also provides a practical assessment of sample size variation among dredge and tong sampling gears, which highlights the impact of sample size on dredge and tong density estimates.
Conclusions
This is the first tong and dredge comparison in Texas estuaries consisting of a range of reef types and oyster densities. In addition, the study pairs this gear comparison with acoustic surveys to characterize the study sites. Overall, this study provides information on the variation in performance of dredge and tong sampling, which will help fisheries managers understand the complexities of oyster sampling biases across these two sampling gears and choose the most appropriate sampling gear given the purpose and nature of the monitoring and management scenario.