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In Chile, the IMTA approach started in the late 1980s. The first attempt considered the development of land based intensive marine systems using pumped seawater to intensively culture trouts (Oncorhynchus mykiss) at a stock ing biomass of 35 kg m 3. The fish effluents were then used for the cultivation first of oysters (Crassostrea gigas) and second of the agar producing alga Gracilaria. The results showed that tank cultivation of trouts was

Figure 11 Atypical modern Atlantic salmon (Salmo salal) farm, with an automated feeding barge, in the Los Lagos Region of southern Chile. Photo by A. Buschmann.

technically feasible and economically viable if a high density of fish could be reached and the size of the farm was sufficiently large to pay for the investment. In addi tion, the oysters and the algae were able to reduce nitrogen and phosphorus significantly.

The cage culture approach for salmon species started in the early 1990s and developed at an explosive rate, to the point that Chile is now the second largest salmon producer in the world, after Norway (Figure 11). This explosive growth prevented the adoption of alternative farming strategies, like IMTA, as the industry had no immediate incentive to modify a very successful financial story. Following the tendencies in Northern Hemispheric countries, concerns about the unsustainable nature of fed aquaculture in Chile started to be raised in the second half of the 1990s. This encouraged the development of studies integrating the cultivation of oysters and seaweeds (Gracilaria and Macrocystis). The first trials were successful and demonstrated that an IMTA approach was an addi tional way for developing a more sustainable aquaculture approach for the country.

It has, however, not been easy to adopt an IMTA approach in Chile. Like oriental countries, Chile has a long tradition of shellfish and seaweed consumption; however, the price for these goods is very low, therefore, they cannot be suggested as an interesting business for investors. For this reason, the Research Centre for Coastal Resources and Environment (i mar) of the Universidad de Los Lagos, in Puerto Montt, has a plan of action parallel to the IMTA research programme, which involves publishing and obtaining patents related to novel uses of seaweeds to encourage the farming of these organisms. The development of abalone cultivation is presently emerging in Chile, adding an extra pressure on natural resources of seaweeds as a source of feed. A

Figure 12 The kelp (Macrocystis pyrifera) cultivated on long lines near Atlantic salmon (Salmo salar) cages in southern Chile. Photo by A. Buschmann.

pilot scale farm (4-5 ha) is already producing the brown alga Macrocystis (Figure 12) and has demonstrated its technical and economic feasibility. The implementation of these new cultivation approaches will probably take place in the coming years and it is important that research keeps up with development in order to promote better understanding of the results.

Basic and applied research must come together to create the conditions necessary for the establishment of a sustainable aquaculture activity in Chile and other parts of the world. Besides the development of demonstration units and applied research to clearly show farmers and regulators the benefits of IMTA, basic research on, for example, nutrient uptake and assimilation, remains neces sary. The environmental requirements for the growth of seaweeds and shellfish may not be the same as for maxi mizing their biofiltering capacity. Their nutrient recycling efficiency can be optimized by manipulating the culture conditions (depths, relative position with respect to the salmon cages in relation to the prevailing currents, distance from the cages, and culture density), allowing for both a high biofiltering efficiency and increased biomass production capacity to make the IMTA approach commercially attractive.

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