Agriculture and Environment: Salmon

Better Management Practices: Closed Production Systems

Some have suggested that in the final analysis, completely closed systems for the containment of contaminated wastes is the only sustainable solution for salmon production (Staniford 2002).

Enclosed, land-based salmon farming can reduce or eliminate many of the problems specific to net-cage production systems.


Salmon farmed in net cages escape into the wild. This impact, and the genetic and disease issues that it raises, would be eliminated with on-shore closed systems. Similarly, wastes that are discharged into the ocean in the net-cage system would be captured as the water leaving the land-based tank is filtered.

These nutrient-rich wastes could potentially be recycled for agricultural use. The industry, and ultimately the consumer, rather than the environment or the "public" more broadly, would pay for the cost of waste disposal.

Salmon raised in closed containment systems
AgriMarine Industries Inc. in Canada recently made the first sale of Pacific salmon raised in a land-based, closed containment system (Smyth 2002). The company raises salmon in concrete tanks, in which seawater is pumped in and oxygenated and outgoing water is filtered.

This system produces healthy salmon but is far more expensive to operate than the standard cage production system. While AgriMarine's salmon was sold at a higher price and marketed as "eco-friendly," it is not clear that such a system is economically viable over the long term (Smyth 2002).

Avoiding pumping costs
The most complete study, to date, on the viability of land-based salmon aquaculture was undertaken in the Bay of Fundy (ADI Ltd. et al. 1998). The large tides in the region were seen as an asset because they could move water into reservoirs from which it could flow by gravity into salmon tanks with no pumping costs. Pumping water is a very large expenditure for land-based aquaculture systems.

The study assumed that production would follow standard industry practices (e.g., stocking densities, feeding and growth rates, etc.) It was also assumed that the factors that would most affect such operations were the price of salmon, the rate of return, the up-front capital costs (e.g., investing in dams and seawalls to hold and move the water), the growth of the fish, and the cost of money.

The only scenarios modelled that showed a positive cash flow in 5 years were those that grew transgenic salmon. These salmon grow faster and far bigger than the animals used today. Even with transgenic animals the scale of operations would have to be increased considerably to make the operations profitable.

While such systems may not work for salmon unless the price increases (which is unlikely), it may work for other, higher-valued species. In fact, this system might well have worked for salmon early on when prices were much higher than they are today. What this means is that with the current level of environmental subsidies for salmon aquaculture in many parts of the world, it may be impossible to go back to more sustainable production systems.

Limitations of using land-based systems
Another important issue is that the proposed closed system has some unique implications. It must be located in areas with severe tides, and these areas must, in turn, be located near rather flat terrestrial areas where land-based farms can be established. More importantly, the land-based systems require production units and large tracts of land that would be rarely available in coastal areas anywhere in the world without considerable conflict with existing residents.

Norway is reported to have considered land-based systems, but the country eventually abandoned the idea based on the belief that sufficient land was not available. As a consequence it was assumed tat producers using closed systems would be forced to stock at higher densities. Such densities, it was felt, would lead to very real risks of disease outbreaks (Whoriskey 2000).

Closed-bag-systems
Another closed system that may offer more hope is the use of closed containment systems in open water. These systems amount to little more than large plastic bags in the water column. Water is pumped into and out of the bag to provide oxygen for the fish.

The shape is maintained by the force created by a small hydraulic head pumped into the bag. Such bags offer a number of environmental benefits. Seals and other predator attacks are reduced because animals no longer see the fish through the opaque bags. Waste can be collected and removed from the bottom of the bag rather than released into the water.

Finally, fish raised in bags have fewer sea lice problems than those raised in open net cages (Whoriskey 2000). Closed-bag-systems have been experimented with in both eastern and western Canada. To date, this system of production appears to be expensive to install and operate. This is a deadly combination give the overall decline in salmon prices.

Credits

Extracts from "World Agriculture & Environment" by Jason Clay - buy the book online from Island Press

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