Studies on food-limited growth in juvenile shellfish using novel aquaculture approaches

Growth and survival of Mercenaria mercenaria seed in three marinas and a control site were compared with those in a hatchery-based upwelling system. Seed were grown in mesh bags held in cages suspended below floating docks. Growth rates varied greatly (2% to 12% per day) and survival was excellent at all sites. The biological and economic feasibility of culturing seed under floats in marinas for final grow-out in certified waters was demonstrated.;The same cages were used in a 20-week study of the growth rates of three species of juvenile shellfish (Crassostrea virginica, Mercenaria mercenaria and Argopecten irradians irradians) at three locations along a food concentration gradient. Average tidal current speed was calculated for each site and temperature, total seston, particulate organic matter, and chlorophyll were measured weekly. Food-limited shellfish growth rates at the three locations were not significantly different despite a three-fold difference in chlorophyll concentrations. Higher current speeds compensated for lower food concentrations resulting in nearly identical horizontal chlorophyll fluxes at the three locations. Correlations between shellfish growth and the food flux variables were stronger than those with the food concentration variables, corroborating the Grizzle and Lutz horizontal seston flux model.;A flow-through flume was constructed to study the growth response of Crassostrea virginica and Argopecten irradians exposed to varying degrees of food limitation caused by downstream depletion. The bivalves in each stage of the flume removed a constant percentage of the available food over a wide range of concentrations. Variations in growth and condition index were linearly correlated with ration consumed in the downstream compartments. Concurrent field studies showed similar growth and condition index responses to resource competition associated with varying initial stocking densities in a commercial shellfish aquaculture operation.;Studies were conducted to examine the feasibility of culturing shellfish in mesh-bags held in on-bottom cages. A novel approach to shellfish aquaculture management was developed and commercialized. The approach minimizes multiple-use conflicts by avoiding the need for conventional fixed aquaculture leases by treating the cages as transient-gear. The concept and methods were described and an economic model based on four years of data was presented.