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Jun 2010
A New Approach to Sustainable Aquaculture
Herminio Muñiz

The world is hungry for fish. Faced with declining wild stocks, the fishing industry is giving way to aquaculture, or fish farming, which produced close to 53 million tons of fish in 2006 alone (half of all fish consumed in the world). The worldwide industry is growing at an average of 6.8 percent per year, making it the world’s fastest-growing food sector. But this growth has come at a cost: Chemicals and antibiotics used in fish farms seep into surrounding waters; fecal contamination causes harmful algal blooms; sensitive coastal and wetland areas are disrupted or destroyed; and wild fish stocks are depleted in order to provide feed for carnivorous domesticates.

What options are left to conscientious consumers? Choosing your fish is like choosing a cut of meat: You need to know your farm. Some fish farms are able to maintain profitability and improve the quality of their products and still minimize their environmental impact.

Such is the reasoning behind Veta la Palma fish farm. Veta la Palma is located in southern Spain and lies at the center of the Guadalquivir River’s estuary marshes. Twenty centuries ago, under the Roman Empire, this land was a large coastal lake known as Lacus Ligustinus. Gradually, the input of river-borne sediments and marine deposits laid down by the tide silted up the lake and formed a huge and muddy no man’s land. The area is currently a floodable plain, pockmarked with depressions filled by seasonal rains and surrounded by natural drainage canals (locally named caños) and artificial waterways bordering smaller, slow-moving interfluves (esteros). The flat relief is interrupted only by old levees (vetas) rising one or two meters above the plain.

In other words, this wild and rough territory, stretching along the Guadalquivir River to the east and Doñana National Park to the west, is the perfect place for a fish farm.

Grass-shrimp fisherman (by Antonio Liébana).jpg
Antonio Liébana

When our company, Pesquerías Isla Mayor, S.A. (PIMSA) bought Veta la Palma in 1982, the original wetland ecology had been seriously damaged by both natural silting-up and manmade channels intended to control annual flooding so that cereal agriculture could thrive. We decided to initiate an ambitious aquaculture project that would reverse water flow in the drainage network, adapting these channels to irrigation. The result has been a hydraulic management model in which aquaculture and conservation are well integrated.

At present, we have 45 rectangular, 70-hectare ponds totaling 3,200 hectares of floodable terrain, making our aquaculture installations the largest in Europe. Ponds are connected to each other and to the Guadalquivir River by means of a complex 300-kilometer channel network. To maintain oxygenation and water quality, 1 million cubic meters of tidal water are pumped daily from the river estuary through the whole system. This carefully managed artificial wetland supports a rich and nourished flora and fauna, including dense communities of microalgae and invertebrate species, which are the foundation of our aquaculture products. The species we cultivate are typical of the Guadalquivir estuary and include sea bass, sea bream (Sparus aurata), meagre (Argyrosomus regius), sole fish (Solea solea, S. senegalensis), shrimp (Palaemonetes varians), eel (Anguilla anguilla) and mullet (Mugil cephalus, Liza ramada).

The ponds annually yield around 1,500 tons of fish and shrimp, at the same time supporting the hydrology and ecology of the Guadalquivir marshes and the greater Doñana ecosystem. In an uneven land, we have created a mosaic of habitats defined by variations in soil conditions and humidity: areas of natural salty marsh, partially or fully flooded, dominated by salt-loving plants; lower-lying areas (sweet marshland) with stronger seasonal variation, where reeds and marshy shrubs grow densely; and a first-rate 3,200-hectare water sheet for aquaculture, where waterbirds congregate in the thousands year-round. In addition, we have built more than 100 islands within fish-farming ponds to serve as nesting sites for waterfowl. Some 30,000 birds were recorded in 1984; 600,000 birds now routinely visit in the fall months, attracted by the abundance of fish and shrimp.

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Herminio Muñiz

The hydrological stability of extensive fish-farming ponds promotes a massive development of microalgae that filters excess organic matter from the water, particularly nitrogen and phosphorus produced as waste (i.e., fecal contamination), thus avoiding harmful algal blooms. Microalgae, as well as sediment-linked algae and bacteria that take part in decomposition, are consumed by a varied aquatic microfauna including worms, insects, crustaceans, and small fishes that themselves are the natural diet of our cultivated fishes. Omnivorous fishes and the approximately 30,000 filter-feeding pink flamingos that use Veta la Palma as feeding grounds indirectly help nutrient recycling in the water and make this system more efficient than standard intensive aquaculture operations.

When we first acquire fingerlings of sea bass, sea bream, meagre, and sole fish from external hatcheries (mullets and eels naturally enter from the Guadalquivir estuary), we release them into 500-square-meter pools situated beside the near-natural ponds. When the fishes reach a certain size, they are moved to the ponds in order to keep a low culture density. They continue to grow there for about three years, feeding off wild shrimps and other aquatic organisms, until they reach one kilogram (conventional fish farms typically harvest a fish once it weighs only 400 grams). Low culture density and an antioxidant-rich natural diet minimize ecological stress during the growing period and increase fish resistance to diseases, ultimately reducing the input of chemicals and antibiotics as well as the risk of disease spreading to wild fish. While the diets of carnivorous farmed fish only increase the threat to already depleted wild fish stocks, our polyculture system—in which fish feed on shrimps and microorganisms naturally occurring in the water—does not add to the pressure on overfished seas.

By working closely with the natural ecosystem, Veta la Palma avoids many of the pitfalls of conventional, intensive fish farming. We believe that our fish farm could be a useful model for future plans to regenerate the disrupted marshland areas and coastal wetlands of Spain and Atlantic Europe. At Veta la Palma we are not only making consumption and conservation compatible—we are moving toward a new outlook on conservation and development where the careful use of natural resources, such as water and land, can generate economic profits while enhancing a wide range of environmental values.

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