Combined effects of temperature-salinity on larval survival of the Eastern oyster Crassostrea virginica in the Maryland portion f the Chesapeake Bay (USA)

AB5TRACT Oyster landings in the Maryland portion of the Chesapeake Bay have declined by more than 50­ fold since the early part of the century, despite intensive management efforts. The am\ual shell repletion program is the most critical programmatic element to effect recovery of the ailing Eastern oyster Crassotrea Tlirginica stock and fishery. The overall efficacy of shell repletion management depends primarily on the success of spat settlement on the planted shell, and furthermore on their survival rate. The Operations Research techniques and mathematical programming developed by Rothschild et al. (1991) attempt to maximize spat recruitment to the oyster stock subject to a series of operational constraints. Allocation and timing of shell deployment are the most critical issues. To he truly efficient, this approach should incorporate the principal biological constraints affecting oyster production. A modelling approach is proposed to consider the spatial and temporal distribution of temperature salinity over the Maryland portion of the Chesapeake Bay. We defined three models according to geographic regions in the Bay (i.e., Upper, Middle, Lower Bay) to characterize the specific pattern of potential larval survivorship. Stations located in Lower Bayon bath Eastern and Western shores show the highest potential for larval survivorship. Higher percentages, also maxima, are reached earlier in the season and last longer at southern locations. The sharp ascending phase in survivorship in May-June tends to decline with increasing latitude in the Lower Bay region. Mid-Bay locations rarely reached the 100% of larval survivorship and maxima are reached later in the season than at 50uthern locations. Descending phase is similar on both Lower and Mid-Bay regîions with a sharp decline in September. In Upper-Bay, Eastern locations are more favorable than Western areas. Larval survivorship on oyster bars located north from the Chesapeake Bay Bridge is particularly low with a 45% maximum. These areas are unlikely self-sustainable in spat recruitment and probably rely on episodic transport of older larvae from 50uthem areas. Then, recommendations are proposed to maximize the yield of the current shell and sanctuary programs, and al50 to define the future research priorities. Modelling streamflow into Chesapeake Bay would likelyallow salinity prediction 50 as ta determine optimum sites and timing for shell planting on a yearly basis. Stock assessment and larval monitoring are al50 strongly recommended to maximize the current management cost-effectiveness.