Gear and survey efficiency of patent tongs for oyster populations on restoration reefs

Abstract

Surveys of restored oyster reefs need to produce accurate population estimates to assess the efficacy of restoration. Due to the complex structure of subtidal oyster reefs, one effective and efficient means to sample is by patent tongs, rather than SCUBA, dredges, or bottom cores. Restored reefs vary in relief and oyster density, either of which could affect survey efficiency. This study is the first to evaluate gear (the first full grab) and survey (which includes selecting a specific half portion of the first grab for further processing) efficiencies of hand-operated patent tongs as a function of reef height and oyster density on subtidal restoration reefs. In the Great Wicomico River, a tributary of lower Chesapeake Bay, restored reefs of high- and low-relief (25–45 cm, and 8–12 cm, respectively) were constructed throughout the river as the first large-scale oyster sanctuary reef restoration effort (sanctuary acreage > 20 ha at one site) in Chesapeake Bay. We designed a metal frame to guide a non-hydraulic mechanical patent tong repeatedly into the same plot on a restored reef until all oysters within the grab area were captured. Full capture was verified by an underwater remotely-operated vehicle. Samples (n = 19) were taken on nine different reefs, including five low- (n = 8) and four high-relief reefs (n = 11), over a two-year period. The gear efficiency of the patent tong was estimated to be 76% (± 5% standard error), whereas survey efficiency increased to 81% (± 10%) due to processing. Neither efficiency differed significantly between young-of-the-year oysters (spat) and adults, high- and low-relief reefs, or years. As this type of patent tong is a common and cost-effective tool to evaluate oyster restoration projects as well as population density on fished habitat, knowing the gear and survey efficiencies allows for accurate and precise population estimates.

Crassostrea virginica dredge efficiency in Texas estuaries

“…Dredges provide a low-cost, rapid method for assessing oyster populations, but dredge-estimated oyster densities can be affected by several factors (e.g., tow speed, line length, dredge width, etc. ), leading to dredges being labelled as unreliable tools for accurate oyster surveys (Schulte et al, 2018). However, dredge-estimated oyster densities were often less variable than quadrat-estimated densities in this study, which can be attributed to the fine-scale (< 10 m) spatial homogeneity that is not detected by the larger area sampled by an oyster dredge.…”

Efficiency of Hydraulic Patent Tongs for Surveying Restored Eastern Oyster Reefs in Harris Creek, Maryland

“…Chai et al (1992) found that density estimates from divers and hydraulic patent tongs were not significantly different (i.e., 100% hydraulic patent tong efficiency) and that average densities derived from each gear type were similar. Our estimated hydraulic patent tong efficiency was also lower than that of Schulte et al (2018), who compared mechanical patent tongs, which use a spring to close instead of hydraulics, to FIGURE 3. Estimated box natural mortality rates (%) by site for restored oyster reefs sampled by diver and hydraulic patent tongs in Harris Creek, Maryland.…”

“…For this approach to provide unbiased estimates of density, both sampling methods must collect and retain all eastern oysters in the area sampled. Previous studies have evaluated the efficiency of mechanical patent tongs (Schulte et al 2018) and hydraulic patent tongs relative to divers and dredges (Chai et al 1992). The results of these studies differed, with Schulte et al (2018) finding that the efficiency of mechanical patent tongs was about 76% (i.e., 76% of the oysters caught in the sample area were captured by the gear) and Chai et al (1992) finding no significant difference between divers and hydraulic patent tongs.…”

“…Previous studies have evaluated the efficiency of mechanical patent tongs (Schulte et al 2018) and hydraulic patent tongs relative to divers and dredges (Chai et al 1992). The results of these studies differed, with Schulte et al (2018) finding that the efficiency of mechanical patent tongs was about 76% (i.e., 76% of the oysters caught in the sample area were captured by the gear) and Chai et al (1992) finding no significant difference between divers and hydraulic patent tongs. However, the mechanical patent tongs used in Schulte et al (2018) are different than hydraulic patent tongs and eastern oyster densities were relatively low in Chai et al (1992), which may cause their results to be not applicable for restored oyster reefs in Maryland.…”

Monitoring program design for data‐limited marine biogenic habitats: A structured approach

“…Fast-growing and abundant benthic species such as seagrasses, macroalgae, and bivalves can be destructively sampled by extractive (manual or excavating) methods for further examination, including taxonomic identification and determining biomass and biomarker levels (Molina Hernández & van Tussenbroek, 2014;Schulte, Lipcius, & Burke, 2018;Tsiamis et al, 2013). Extractive methods can also be used to sample slow-growing species where visual census methods are not feasible, such as in turbid waters (Moura et al, 2016).…”