adminsteady annual rate of 8 to 10 percent for the past three decades. Proponents for the industry claim that aquaculture is the only serious option for feeding a future global population of 9 billion. Aquaculture critics claim that fish farms are polluting and unsustainable because the amount of feed required to produce a similar weight of harvested fish will further strain deteriorating wild fish stocks.
Unlike all other forms of aquaculture, farmed shellfish have been identified as the only sustainable form of aquaculture that has no negative impact on the environment. Rather, shellfish aquaculture operations actually improve water quality by filtering out pollutants, sediments, and phytoplankton from the water column.
Moreover, shellfish are environmentally sustainable since they neither require fish feeds, compete with wild species for food, nor consume more protein than they produce. Oyster shellfish were once the global ecosystem engineers enabling prosperous habitats for other species. Amazingly, a single adult oyster can filter up to 50 gallons of water each day removing nitrogen and other nutrients from the water for mitigating eutrophication and helping control and prevent harmful algal blooms.
While Pacific oysters (Crassostrea gigas) originate from Japan, this species has been intentionally introduced in many areas of the world to replace native oysters that have been decimated by disease. Pacific oysters are typically more resistant to the diseases that afflict native oysters and their relatively fast growth rate and high meat yield makes them ideal for farming.
Globally, Pacific oysters have become the gold standard for replacing stocks of indigenous oysters severely depleted by over-fishing or disease, and to create an industry where none previously existed.
According to the Food and Agriculture Organisation (FAO), subsequent to their creating the above map, Pacific oyster introductions have also been recorded in: Ecuador, Belize, Costa Rica, Puerto Rico, the United States Virgin Islands, Brazil, Israel, Philippines, Malaysia, Romania Ukraine, Seychelles, Fiji, French Polynesia, Guam, Palau, Samoa, and Vanuatu.
On the West Coast of Africa, the hardy Pacific oyster species has not been recorded north of Namibia; yet it can survive at salinities between 10 and 35 percent and has a broad temperature tolerance ranging between 28 to 95 degrees Fahrenheit. Offshore surface water temperatures for West Africa range from 56 to 82 degrees based upon 25 years of data.
By extrapolating temperature data with the scientific certainty that oysters grow faster in warmer water, the Pacific oyster could anecdotally reach harvestable size within 6 months throughout the region. This is because oysters are “cold-blooded” so their metabolic rate increases with temperature, which translates into faster growth rates.
Potential for Open Ocean Oyster Farming in West Africa A feature article published in the July, 2011 issue of Intrafish, Lifting the Veil on Africa – Aquaculture’s Next Frontier, reported:
“Africa has all the characteristics needed to turn itself into an aquaculture force to be reckoned with. Just to maintain the present per capita consumption of fish in Africa, aquaculture will have to expand by 250 percent in the coming years.”
Only by moving aquaculture offshore will this enormous demand for fish be met for helping feed West Africans in the future. Near-shore production has limited capacity for growth due to competition for space and uncertain water quality. Offshore shellfish farms have shown higher growth rates, better meat yields, and heavier production compared with inshore farms.
This is attributed to the lower stress, reduced turbidity and better water exchange experienced at the offshore farms.
While commercial shellfish cultivation is currently non-existent in West Africa, there are lessons to be learned from the 2010 report published in the Journal of Shellfish Research “The History and
Status of Oyster Exploitation and Culture in South Africa”: After years of experimental trials, South Africa now follows the global trend of importing the much hardier Pacific oyster because there was insufficient knowledge on culturing indigenous species.
The introduced Pacific oyster is now widely farmed and has become naturalised in estuaries along the southwestern coast. Approximately 2 million Pacific oysters were annually produced in South Africa throughout the 1970s and early 80s increasing to about 8 million in 1991. The market for cultivated oysters in South Africa has grown steadily during the past decade but production has not kept up with demand.
Introducing the Fittest for Feeding West Africa The Pacific oyster with its large size, vitality, resilience to adverse conditions, resistance to deceases, rapid growth and reproductive capacity has been a tremendous success for cultivation making it the most widely farmed oyster species in the world.
However, the introduction of a stronger foreign oyster has critics claiming harmful environmental impacts because it overtakes the weaker native species.
In a recent New York Times opinion piece, Mother Nature’s Melting Pot, author and anthropologist Hugh Raffles articulately spins the controversial invasive species issue as having positive potential:
“But just as America is a nation built by waves of immigrants, our natural landscape is a shifting mosaic of plant and animal life.” – The African Executive.
Online Reporter