Forage fish

Forage fish, also called prey fish or bait fish, are small pelagic fish that feed on planktons (i.e. planktivores) and other small aquatic organisms (e.g. krill). They are in turn preyed upon by various predators including larger fish, seabirds and marine mammals, this making them keystone species in their aquatic ecosystems.

The typical ocean forage fish feed at the lower trophic level of the food chain, often by filter feeding. They include particularly fishes of the order Clupeiformes (herrings, sardines, shad, hilsa, menhaden, anchovies, and sprats), but also other small fish, including halfbeaks, silversides, smelt such as capelin and goldband fusiliers.

Forage fish compensate for their small size by forming schools. Some swim in synchronised grids with their mouths open so they can efficiently filter plankton.^[1] These schools can become immense shoals which move along coastlines and migrate across open oceans. The shoals are concentrated energy resources for the great marine predators. The predators are keenly focused on the shoals, acutely aware of their numbers and whereabouts, and make migrations themselves that can span thousands of miles to connect, or stay connected, with them.^[2]

The ocean's primary producers, mainly contained in phytoplanktons, produce food energy and biomass photosynthetically from sunlight and are the raw fuel for the ocean food webs. Forage fish transfer this energy by eating the plankton and becoming food themselves for the top predators. In this way, forage fish occupy the lower-central positions in ocean and lake food webs.^[3]

The fishing industry sometimes catch forage fish for commercial purposes (i.e. as seafood), but primarily for use as feeder fish to raise more valuable piscivorous animals (e.g. salmon farms). Some fisheries scientists are expressing concern that this will affect the populations of predator fish that depend on them.^[4] The practice of harvesting forage fish can also be a sign of overfishing as fish stocks of larger species in the fisheries are depleted thus forcing the industry to start fishing down the food web.