Overfishing threatens critical link in the food chain

The fish near the bottom of the aquatic food chain are often 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 - both for the forage fish themselves and for 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 of fish. While this is effective for guarding against ocean predators, it makes them easy prey for modern fishing fleets equipped with purse seine nets that can cinch up an entire school at once. What's 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.