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ENV100Y5 (690)


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University of Toronto Mississauga
Monika Havelka

Aquaculture- Can it replace wild fisheries? Is aquaculture the magic bullet? The state of wild capture fisheries  Relationship between aquaculture (increasing) and wild capture fisheries (decline)  Technology and intensity of effort is improving, and despite pressures to capture more, there isn’t because we have exploited what’s available for wild capture fishers  Efforts to control exploitation of wild capture fisheries has been largely ineffective; an increasing proportion of important fish stocks are depleted for below their optimal densities for high production; another half of stocks are fully exploited; total yield may be going down despite increasing capture effort  Relative contribution to aquaculture and culture fisheries to food fish consumption (decreasing due to exploitation and increase in population)- China has a big impact  Net exports of selected agricultural commodities by developing countries (biggest export is fish)  World agriculture production and relative share by culture environment (what kind of aquaculture is happening out there- 2/3 is freshwater, marine is in the middle, and brackish water is low)- Freshwater aquaculture is much bigger than marine aquaculture  Canada is distant 3 to Norway and Chile in salmon production (up to 2 million tonnes out of worldwide total of 80 million tonnes)  Top ten exporters and importers of fish and fishery products (China is growing, Canada is not growing as much)  Overall, Canada’s aquaculture activities are fairly stable How’s it done A tour of aquaculture activities  Cages- Mesh open to water flow beneath surface; food delivered by operator; wastes drop out bottom of cage to ocean bottom o Eastern US cages- covered to deter predators, surrounded by protective net (larger cages designed to prevent debree from floating in) o Tuna rearing cages, young tuna in the cage (small and easily to catch) o A tender services each cage twice daily o All of these tubs of fish are fed to the tuna twice daily (way to reduce tuna mortality and finding them when they’re at a very large size but requires huge investment in wild food)  Molluse culture in Tasmania (basket of clams in suspended positions so that they are partially exposed so they can be tended with tides) o Molluse (clams , oysters) aquaculture has low impacts because no supplementation food is required Intensity and Scale of aquaculture  Primative (low intensity) aquaculture has low yields (ex. Shrimp: 0.1 kg m^-2y^-1)  Intensive modern aquaculture yields: 4 jg m^-2y^-1 (50-60X the most productive river)  At $20/kg wholesale, values of sales: $800,000/ha^-2y^-1  Aquaculture facility near Great Barrier Reef while spots are aeration devices to maintain oxygen concentrations An industry in flux Systemic Problems with Aquaculture:  Why don’t wild populations grow at aquaculture densities?  Density and productivity of food rarely occurs o At a single location in nature o Or within feasible foraging distances o Reliably through time  Nutrients, oxygen and carbon dioxide can’t be supplied at sufficient ra
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