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Archived – Nova Scotia study aims to match shellfish stocking density to food availability
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Low-cost monitoring devices under development
Monitoring arrays gather the data needed to develop the low cost prototypes.
It's in no one's best interests to have shellfish operations depleting phytoplankton food sources in bays off the Canadian coast, but it can be an expensive proposition to buy all the highly-sensitive monitoring equipment to assess the right amounts of biomass to match a particular area's natural resources.
"Optimization of yields depends on matching the stocking density of shellfish to the availability of food," said oceanography professor Dr. John Cullen, Chair of Environmental Observation Technology at Dalhousie University in Nova Scotia.
"Too many shellfish per acre will deplete the food resource and growth will be low; too few shellfish and harvests will be less than nature could support."
So doctoral student Diego Ibarra is working under Cullen on a research project to come up with cost-effective measuring systems which will be sufficiently accurate to help growers keep a handle on the most suitable levels of biomass for their different sites.
According to Cullen, as lead investigator on the project, much of the work is being done by Ibarra, who has indicated an interest in coming up with appropriately inexpensive devices for the industry, based on more sophisticated devices generated by Cullen and others from previous oceanographic studies on the areas around shellfish farms.
Diego Ibarra deploys monitoring array.
Some of that work with larger, higher-tech observation and monitoring systems is still continuing, in part to aid Ibarra in his research, said Cullen; and Dalhousie now has what Cullen refers to as "an ocean observatory" using a series of buoys in Ship Harbour, Nova Scotia.
The observatory consists of four buoys fitted with automated measuring devices to collect information on the oceanographic, meteorological and optical properties of the water, some of it being transmitted directly back to data banks at Dalhousie for storage and retrieval.
Cullen and Ibarra are particularly monitoring the clarity and colour of the upper few metres of the ocean in the bay directly around mussel rafts in the area.
Cullen said the work will allow researchers to make their own estimates of the concentrations of phytoplankton populations and of other water-borne substances - such as sediment in the immediate vicinity of shellfish cages, which will also enable project personnel to calculate the uptake of the microscopic phytoplankton by shellfish at the operations.
"It's basically a new, automated approach to obtain nearly-continuous recording of the properties of the water," said Cullen, adding that water samples are also taken to ground-truth the accuracy of their sensors and data.
"The instruments on the buoys give us very detailed measurements of the optical properties of the water, and we compare them with simultaneous findings from people going out and sampling the water," he said.
"We use these comparisons to come up with equations which will let others estimate the concentrations of materials in the water at their sites, using comparatively inexpensive light and clarity-monitoring instruments being developed by Ibarra," said Cullen.
Cullen said that the much larger and more high-tech instruments require comparatively large, moored buoys in the bay, but Ibarra has managed to devise prototypes for much smaller, less costly and less-detailed instruments which can be hung at different depths from much smaller buoys.
An "ocean observatory" has been created by using a series of buoys in Ship Harbour, Nova Scotia.
The two-year research project, which springs from studies dating back to 2000 is being conducted with the help of AquaPrime and the Satlantic Inc instrumentation company. The study is due for completion next spring, but is to be extended to both British Columbia and Spain as Ibarra works towards his doctoral degree in about two years' time.
Research team: John Cullen, Diego Ibarra and Penny Barnes, with partner Satlantic, Inc. For information contact John Cullen (Email: John.Cullen@Dal.CA). Submitted by AquaNet.
Jan.'05-Mar.'08
