Remote setting is a technique developed in the Pacific Northwest in the late 1970s to produce spat-on-shell oyster seed for restoration and aquaculture, consisting of two main phases: (1) larval setting, in which larvae attach to a substrate; (2) nursery period, in which oysters seed are grown until they are ready for planting. This technique was successfully introduced to Chesapeake Bay in the mid-1980s and it is currently used in Maryland since then. However, the duration of nursery period still represents a controversial aspect of remote setting, with knowledge gaps surrounding the adequate holding time for newly settled spat in the setting facilities. While longer holding times of oyster spat in the nursery may promote spat survival, they also require maintenance and resources, like food and space, that can increase costs of production. On the other hand, a premature deployment could affect spat survival after planting, jeopardising the whole production operation.
An experiment was performed at the setting pier of the Horn Point Oyster Hatchery (HPOH) in July 2024 to investigate the effect of holding time on the survival of Crassostrea virginica and to determine an optimal holding time that promotes spat survival and minimizes costs and impacts on production. Larvae from two different broodstock mixes (2 treatments) were added to six setting tanks (3 replicates/treatment). Following settlement, spat-on-shell were kept in the tanks for 5, 11, and 17 days (3 holding times) before being deployed at the Cooperative Oxford Lab pier by the Oyster Recovery Partnership (ORP), in accordance with the current planting practices used by ORP. For each holding time, a subset of settled spat were counted and measured before planting, as well as 48 hrs, 1 month, and 4 months after planting, and will be counted again after 1 year.
The results of this study have the potential to provide new information on the optimum holding time of C. virginica seed in nursery facilities, which could lead to cost-effective improvements of remote setting practices that support oyster restoration, aquaculture, and commercial fishing activities in the Chesapeake Bay and beyond.