Forage fish are small, schooling marine organisms that occupy a central position in ocean food webs. In the strict sense, they are small pelagic fishes—such as herring, sardines, anchovies, and sand lance—that feed on plankton and are in turn consumed by larger predators. More broadly, the concept extends beyond true fish to include other mid-trophic-level prey such as squid and crustaceans like krill, which play the same ecological role of transferring energy upward through the food chain. In the Atlantic Ocean, key forage species include capelin, sand eels (sand lance), Atlantic herring, sprat, and juvenile gadids such as young cod and haddock. Capelin, for example, graze on plankton and form dense schools that are heavily preyed upon by whales, seals, cod, and seabirds during spawning migrations. Sand eels are particularly critical in the North Sea, forming a primary food source for seabirds including puffins and kittiwakes. In the Pacific Ocean, many of the same groups occur—capelin, sand lance, and herring—but additional dominant species include anchovy, sardine, juvenile rockfish, and Pacific saury. These species often dominate highly productive upwelling systems such as the California Current, where nutrient-rich waters support immense plankton blooms and thus large forage fish populations.
Forage fish are typically distributed in coastal and continental shelf waters, though some migrate offshore or seasonally track plankton blooms. Their abundance is often highly variable, characterized by “boom and bust” cycles driven by oceanographic conditions such as temperature, nutrient supply, and plankton productivity. Despite their small size, they are nutritionally rich—high in lipids and energy—which makes them ideal prey for predators. Their ecological role is fundamental: forage fish act as the main conduit of energy from microscopic phytoplankton and zooplankton to higher trophic levels. A wide array of predators depend on them, including large fish (cod, salmon, tuna), seabirds (especially puffins, auklets, murres), and marine mammals (whales, dolphins, seals). Puffins in particular rely on dense aggregations of small schooling fish like sand lance, capelin, and herring to provision their chicks, making them highly sensitive to fluctuations in forage availability.
Forage fish populations face increasing threats. Industrial fisheries target many species directly for human consumption, fishmeal, and fish oil, sometimes removing large fractions of biomass from ecosystems. Because these species also support predators, overfishing can cascade through food webs, reducing breeding success and survival of seabirds and marine mammals. Climate change compounds these pressures: warming oceans, shifting currents, and marine heatwaves can alter plankton communities, disrupt spawning, and shift forage fish distributions. Such changes have already been linked to seabird breeding failures in both the Atlantic and Pacific.
In sum, forage fish—whether fish, squid, or krill—are small but disproportionately important. Their abundance, distribution, and quality ultimately shape the structure and productivity of marine ecosystems, from plankton to puffins and whales.
