Thesis Defense Seminar - Margaret (Kit) Wheat-Walsh

MARINE BIOLOGY PROGRAM
DEPARTMENT OF LIFE SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI

SUBJECT: A comparison of hydraulic patent tongs and oyster dredges for monitoring oyster reefs in the Mission-Aransas Estuary
GRADUATE ADVISOR: Dr. Jennifer Beseres Pollack

ABSTRACT

The Texas Parks and Wildlife Department (TPWD) currently uses dredge sampling to manage oyster reefs open to commercial harvest. However, dredges have been shown to produce biased sampling data with regard to the density and relative sizes of the oysters collected. In this project, we compared the sampling performance of oyster dredges in reference to hydraulic (patent) oyster tongs. The objectives of this project were to: (1) Compare the density (n m^-2) and size (shell height, mm) of live oysters, articulated shells of dead oysters (boxes), and oyster shells collected using dredges and tongs across varying reef structures (assessed with acoustic mapping procedures). (2) Compare dredge vs. tong-generated metrics and evaluate resulting thresholds for opening and closing oyster harvest areas. (3) Compare the logistics and practicality of dredge versus tong sampling methods for oyster monitoring (e.g., cost, gear maintenance and operation, impacts on staff-hours). Results indicate that dredges show a size bias toward larger shells and oysters, while tongs sample a smaller area and may not accurately represent density across the entire reef extent, particularly for reefs with patchy oyster distribution and where sample size is not adequate. Although deployment, retrieval, and processing for one tong sample takes less time than for one dredge sample, tong sampling requires one additional staff member and approximately 2-3x more samples to see stabilized estimates of density, compared to dredge sampling. Based on this study, tongs may be better suited for more focused (spatially or temporally) sampling initiatives where a greater number of samples and staff time are more realistic. This is the first tong and dredge comparison in Texas estuaries that focuses on monitoring commercially harvested oyster reefs and understanding the ability of tongs and dredges to provide management metrics across a range of reef types and oyster abundances.