Effects of Aquaculture on World Fish Supplies

by Rosamond L. Naylor, Rebecca J. Goldburg, Jurgenne Primavera, Nils Kautsky, Malcolm C. M. Beveridge, Jason Clay, Carl Folke, Jane Lubchenco, Harold Mooney, and Max Troell

Summary

Global production of farmed fish, shrimp, clams, and oysters more than doubled in weight and value during the 1990s while landings of wild-caught fish remained level. Many people look to this growth in aquaculture to relieve pressure on ocean fish stocks, most of which are now fished at or beyond capacity, and to allow wild populations to recover. Production of farmed fish and shellfish does increase world fish supplies. Yet by using increasing amounts of wild-caught fish to feed farmed shrimp and salmon, and even to fortify the feed of herbivorous fish such as carp, some sectors of the aquaculture industry are actually increasing the pressure on ocean fish populations.

The available scientific evidence indicates that some types of aquaculture are on a destructive path that poses a threat not only to wild fish stocks but also to the industry's own long-term potential. One of the most disturbing trends is the rapid expansion and intensification of shrimp and salmon farming and culture of other high-value carnivorous marine fish such as cod, seabass, and tuna. Production of a single kilogram of these species typically uses two to five kilograms of wild-caught fish processed into fish meal and fish oil for feed.

Besides this direct impact on wild fish stocks, some aquaculture as currently practiced degrades the marine environment and diminishes the ecological life support services it provides to fish, marine mammals, and seabirds, as well as humans. These impacts include:

• Destruction of hundreds of thousands of hectares of mangrove forests and coastal wetlands for construction of aquaculture facilities
• Use of wild-caught rather than hatchery-reared finfish or shellfish fry to stock captive operations, a practice that often leads to a high rate of discarded bycatch of other species
• Heavy fishing pressure on small ocean fish such as anchovies for use as fish meal, which can deplete food for wild fish such as cod, as well as seals and seabirds
• Transport of fish diseases into new waters and escapes of non-native fish that may hybridize or compete with native wild fish

As aquaculture production continues to expand and intensify, both its reliance and its impact on ocean fisheries are likely to increase. The balance between farmed and wild-caught fish, as well as the total supply of fish available for human consumption, will depend on future trends in aquaculture practices. If the goal of aquaculture is to produce more fish for consumers than can be produced naturally, then it will become increasingly counterproductive to farm carnivores that must be fed large amounts of wild-caught fish that form the foundation of the ocean food chain. Indeed, non-carnivorous species such as marine mollusks and carps account for most of the current net gain in world fish supplies from aquaculture.

Without clear recognition of its dependence on natural ecosystems, the aquaculture industry is unlikely to develop to its full potential or continue to supplement ocean fisheries. We recommend the adoption of four priority goals for aquaculture:

1. Encourage farming of species lower on the food web – that is, fish with herbivorous or omnivorous diets or filter feeders such as oysters

2. Improve feed management and efficiency in industrial aquaculture systems and develop substitutes for fish-derived feed ingredients

3. Develop integrated fish farming systems that use multiple species to reduce costs and wastes while increasing productivity

4. Promote environmentally sound aquaculture practices and resource management

Governments have a key role to play in developing regulations to protect coastal ecosystems and in reexamining subsidies to unsustainable marine fisheries. Development agencies are strategically placed to help in developing and implementing sustainable production practices and in financing otherwise economically and socially unattainable reforms in developing countries. If public and private interests act jointly to reduce the environmental costs generated by fish farming, present unsustainable trends can be reversed and aquaculture can make an increasingly positive contribution to global fish supplies.