Small fry have big effect: overfishing threatens a critical link in the food chain.

• Author: Roney, J. Matthew
• Position: Ecology

THE FISH near the bottom of the aquatic food chain often are overlooked, but they are vital to healthy oceans and estuaries. Collectively known as forage fish, these species --including sardines, anchovies, herrings, and shrimp-like crustaceans called krill--feed on plankton and become food themselves for larger fish, seabirds, and marine mammals. Historically, people have eaten many of these fish, too, of course, but as demand for animal protein has soared over the last half-century, more and more forage fish have been caught to feed livestock and farmed fish instead of being eaten by people directly. A growing body of scientific evidence suggests that current fishing levels are dangerously high--for the forage fish themselves as well as the predators and industries that depend on them.

Found from the tropics to the poles, forage fish typically travel in dense schools of thousands or even millions, which makes them easy prey for modern fishing fleets equipped with purse seine nets that can cinch up an entire school at once. What is more, forage fish stocks are highly sensitive to environmental change and prone to population crashes, so fishing levels considered safe in good years can be disastrous in bad ones.

Many of the world's largest fisheries focus on forage species, including Peruvian anchovy, Atlantic herring, and chub mackerel. Together, forage fish typically account for more than 30% of the 80,000,000 tons of fish caught annually in the world's oceans and estuaries. Roughly nine of every 10 tons of forage fish hauled in are destined for the "reduction" factory, where they are cooked and pressed to extract the oil; what remains then is dried and milled into fishmeal, a high-protein brownish powder. About 6,000,000 tons of fishmeal and 1,000,000 tons of fish oil are produced each year. Nearly all of the fishmeal is fed to farmed fish, pigs, and poultry. The oil, high in omega-3 fatty acids that are prized for their health benefits, is a popular feed additive and also is employed as a nutritional supplement for humans.

Notwithstanding their large contribution to the world fish catch, forage fish are worth at least twice as much in the ocean as they are on the boat. In 2012, the Lenfest Forage Fish Task Force, an international group of 13 marine and fisheries scientists, released the results of a three-year study, "Little Fish, Big Impact." The authors calculated that forage fish generate nearly $17,000,000,000 per year in reported...