Effects of temporal and spatial variations in seston flux on growth of mussels (Mytilus spp.) in suspended culture in a boreal environment

The Newfoundland mussel culture industry has experienced significant growth over the last five years and growers are beginning to fully utilize the available space on their tenures or in some of the inshore bays. This has raised questions as to the extent to which a site can be stocked and what are the optimum stocking levels. A reciprocal transplant experiment of three mussel populations was undertaken at three commercial aquaculture sites of different hydrographic and environmental regimes. Variations in growth, survival and production were assessed bimonthly in relation to seston flux, temperature and salinity, which were measured over 2--3 weeks at several stations on each site. Calcium Sulfate cylinders were calibrated with S4 current meters to assess relative current speeds. A strong positive relationship was established between cylinder dissolution and actual current speeds providing a useful index for calculating seston flux. Mussel growth and production varied according to season, populations, site and location within a site (ANOVA, p < 0.05). Survival of all mussels exceeded 85% at all sites. Population differences explained variations in survival. Differences in mussel performance were related to the relative seston flux and showed higher as well as more uniform growth and production in areas of higher flux. The importance of relative food flux measurements is discussed in relation to site evaluation criteria and production capacity estimates.