Aquaculture and Biodiversity Conservation

James S. Diana

Professor and Associate Dean in the School of Natural Resources and Environment

University of Michigan

Aquaculture is the most rapid-growing food production system globally, while fisheries have stabilized or declined in recent years. With increasing forecasts of global seafood consumption, as well as increasing population, there is an extreme demand for seafood products, and aquaculture will mainly fill that role. Aquaculture has increased from about 5% of the annual fish harvest in 1980 to about 30% today. This increase has created a series of concerns relating to biodiversity. A recent analysis of issues related to certification of ecologically safe aquaculture products showed seven potentially negative implications on biodiversity:

1. Escapement of aquatic crops and their hazard as an invasive species, exemplified by tilapia escapement from aquaculture systems.
2. The relationship between effluents, eutrophication or pollution of water bodies, and changes in the fauna of receiving waters.
3. Land use, in particular conversion of sensitive areas such as mangroves and wetlands, as well as water use and its loss from surface water systems.
4. Other resource use, such as fish oil and its concomitant overexploitation of fish stocks.
5. Predator control, such as the killing of birds near aquaculture facilities.
6. Genetic alteration of existing stocks from escaped hatchery products.
7. Antibiotic and hormone use, which may influence aquatics species near aquaculture facilities.

In addition to negative impacts, there are a number of very positive impacts of aquaculture on biodiversity. These include at least four major points:

1. The increased production of species reduces pressure on natural stocks and pressure for overexploitation.
2. Cultured crops are often used to reseed depleted natural stocks in aquatic systems.
3. The assimilation of waste products from aquaculture farms often results in increased production, abundance, and diversity of species near farms, particularly in oligotrophic waters.
4. The income generated from aquaculture, reduction of poverty, and improvements in human health may result in the replacement of destructive use patterns, such as slash-and-burn agriculture, with more sustainable patterns, such as aquaculture in ponds.

Examples of some biodiversity-friendly aquaculture systems include those that do not rely on heavy levels of feeding, do not result in large nutrient loadings into receiving waters, and do not use exotic species. Some of these might include semi-intensive culture with no water exchange for low-trophic level species, such as tilapia or carps within the area where they are indigenous or are already well established. A similar system might be the use of seaweed or oysters to remove particulate matter and nutrients from coastal waters and to improve water quality in addition to making a profit. Overall, the future of aquaculture will be limited by the perception of negative environmental impacts and must focus on production systems that will be more sustainable and consider biodiversity as a major issue in addition to economics and social acceptance.