A matrix model for short-term dynamics of seeded populations of sea scallops

Recently, there has been increasing interest in releasing ("seeding") bival ves onto the seabed for purposes of aquaculture or population enhancement. The success of such enterprises has varied greatly and is related to the in teractions between mortality, dispersal, and growth of the organisms. In th is paper, we have constructed a stage-based matrix model for short-term pop ulation dynamics of seeded sea scallops (Placopecten magellanicus). Our goa ls were to predict scallop survival to commercial size and to determine the relative contributions of predation, dispersal, and growth to loss of scal lops. Competing risk theory was used to account for predation by crabs and by sea sears, and for correlations between dispersal and predation (both of which depend on encounters with predators). Density dependence tin the for m of predator functional responses), seasonal variation, and a simple spati al structure were also incorporated into the model. The model was parameter ized from the results of small-scale experiments and tested against indepen dently observed population trajectories. Uncertainty analysis was used to d etermine the effect of parameter sampling error on model output. Sensitivit y analysis indicated that variables affecting predation by crabs were impor tant and that variables affecting intermediate-sized scallops (e.g., large juveniles) were more important than those affecting other size classes. Usi ng perturbation analysis, we ranked alternative management scenarios for in creasing final scallop survival from the most effective to the least effect ive as follows: reducing predator densities, increasing size of seeded scal lops, changing the initial density of seeded scallops, increasing the dimen sions of the site, and changing the season of seeding. Inclusion of seasona l variability in predator densities (thereby converting the deterministic m odel into a stochastic model) did not greatly change final scallop survival .