Virginia Institute of Marine Science
The seed-oyster area is located in a low-salinity sector of the James River where seasonal riverflows and resulting salinities vary widely. Low spring salinities, usually below 10 °/oo in April or May, eliminate most predators and diseases. Prior to 1960, spatfalls were, regular and moderate in intensity each year. High quality seed oysters 2 to 3 inches in size were produced with 1000 to 2000 thick-shelled oysters per bushel for use by private-ground planters. Following the advent of M. nelson! (MSX) in Chesapeake Bay in 1959, setting declined to about one-tenth previous levels and there were spatfall failures in many years. Thick beds of fossil shells provided cultch for setting oysters and little repletion by shell planting was attempted.
In the 1950's a gradient of decreasing spatfall with distance from the mouth of the river was observed. Setting was continuous for about 90 days each year with peak spatfalls in late August or early September. After 1960, setting was irregular by years, and sporadic within the seed area, with no patterns. Larvae were scarce and flushing of larvae out of the estuary appeared to require higher brood-oyster populations.
Oysters -- Reproduction -- Virginia, Oyster culture -- Virginia
Andrews, J. D. (1982) Reproduction of oysters in Virginia. Manuscripts. Virginia Institute of Marine Science, William & Mary. https://scholarworks.wm.edu/reports/2699