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Abstract: The production of cultured Eastern oysters (Crassostrea virginica) in the northern New England states and Canadian Maritime Provinces is hampered by a short growing season, relatively cold water temperatures, and outbreaks of Roseovarius Oyster Disease (ROD). A breeding program at the University of Maine has produced the University of Maine Flowers Select (UMFS) line by selecting for oysters with improved cold water growth performance and resistance to ROD. We conducted two grow-out trials comparing the survival, size, and yield for the UMFS line to two other genetically improved lines of Eastern oysters to assess the suitability of this line outside of the Damariscotta River, where it was developed. In the first trial, oysters were deployed in August just prior to when ROD outbreaks typically occur in Maine among small, seed oysters. We observed substantial differences in yield in this field trial, particularly at study sites located on the Damariscotta River. These differences were due to variation in line-specific survival. The second field trial was deployed in June when ROD has less of an impact on seed oysters. Mortality in this second trial was lower than in the first trial and there was a corresponding higher dependence of line-specific yield on variation in growth. However, there was no line which consistently grew better and had higher yield at all sites. Based on our results, we suggest that breeding programs for Eastern oysters may benefit from focusing on the additive nature of survival variation among lines and placing less emphasis on the relatively subtle variation in line-specific growth. [Copyright &y& Elsevier]