Study on Effects of Mechanical Harvesting Completed

The final report of an Aquaculture Review Council-supported project evaluating alternative farming technology for the sunray venus clam was submitted to the DACS Division of Aquaculture. An 80% increase in sunray venus production was obtained using bottom plants versus bottom bags. Further, the culture period to reach a potential market size of ~2” shell length can be reduced by 15-25% using the bottom plant method. Product quality of sunray venus clams harvested from bottom plants was not compromised as shell deformities, shell breakage, meat grittiness after purging, and shelf life in refrigerated storage did not differ or was improved when compared to sunray venus harvested from bottom bags. The effects on water quality and soil properties by using a small pump-driven device to harvest bottom-planted sunray venus clams were also examined and compared to those associated with harvesting bottom bags. Water temperature, salinity, and dissolved oxygen did not differ during harvests; only turbidity showed any noticeable difference with respect to background condition. Impacts of harvesting activities were short-term as turbidity values returned to background levels within 5-9 minutes post-harvest. Little effect was observed in surface soils with respect to harvestinduced changes in particle size distribution (e.g., sand, silt, clay). Tracks were apparent after harvesting due to soil displacement. Although tracks created by the pump-driven harvester were significantly different than those created by harvesting bags, the depths were shallow (~4 cm) and recovered over an 8-week monitoring period. The science-based information in this report will address barriers to using mechanical harvesting on aquaculture leases and in establishing the sunray venus clam and other potential aquaculture species as feasible complements to hard clams.

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