Growth rates and recovery of hatchery-reared sea scallop, Placopecten magellanicus (Gmelin 1791), spat under a variety of nursery conditions

Levy, Lorelei A. (1999) Growth rates and recovery of hatchery-reared sea scallop, Placopecten magellanicus (Gmelin 1791), spat under a variety of nursery conditions. Masters thesis, Memorial University of Newfoundland.

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Abstract

Nursery culture of the sea scallop, Placopecten magellanicus, is an important transitional phase in hatchery-rearing practices. The Belleoram Sea Scallop Hatchery utilizes the farm-based mesh equipment as the nursery. The purpose of this study was to examine growth rates and recovery of scallops in the farm-based nursery. These factors were monitored with respect to time of year, depth, gear mesh size and type, stocking density, and time of deployment. Remote setting, hatchery flow-through options and ammonia toxicity were also studied for nursery-sized scallops. -- Growth rates of nursery-sized scallops dropped over the winter followed by an increase in the spring. Recovery of scallops (number of live scallops still in equipment after mortality and loss through mesh), however, decreased in the autumn, and leveled off over the winter, which was attributed to handling practices, including the need for acclimation. Growth rates and recovery were highest in the scallops deployed in the largest mesh size which may have been due to better food availability as well as better acclimation by larger scallops. Growth rates were higher in 3.0 mm pearl nets than 3.0 mm collector bags, however, they exhibited the same recovery. The difference in growth may be explained by gear design. No differences in food quantity or temperature existed between 5 and 10 m. however, growth rates were greater at 5 m where fouling was always higher than 10 m. Recovery was similar at both depths. Fouling-induced flow reduction (thus better exploitation of food) or food quality may have influenced growth rates at 5 m. No density dependent effects were noted between 2600 and 5200 spat/bag. Deployment of remote set-or nursery-sized scallops in early to late summer allowed them to have superior growth rates and recovery than deploying during the autumn when temperature and food quantity and quality have dropped. Practicing temperature acclimation and feeding scallops a diet high in essential fatty acids may improve growth and recovery during deployment to sub-optimal farm-based nursery conditions. Scallops held on mesh in flow-through tanks exhibited higher growth than scallops on solid trays. Low growth rates overall in flow-through tanks, however, suggests that flow-through may not be useful for enhancing growth of scallops in autumn sea water temperatures. Summer flow- through trials should be investigated. Ammonia toxicity bioassays suggest that scallops have an increasing tolerance to ammonia with size and that feeding is influenced by the presence of low concentrations of ammonia. -- With this knowledge of important influences of the farm-based nursery, the operators of Belleoram Sea Scallop Hatchery should be able to develop new protocol for scallop nursery practices and thus improve the growth and recovery of their product.

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